Table of Contents

Welcome ...... 5

Programme...... 6 - 9

Invited Lectures ...... 11 - 16

Oral Lectures ...... 17 - 46

Posters...... 47 - )((

Participants...... 10) - 10+

Map with Restaurants...... 10,

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 3 Front view of the Würzburg Residence with the Frankonian fountain. The entrance to the Toscana Hall is located at the right wing of the building.

With Compliments from the 2nd German-British Liquid Crystal Conference, Würzburg 2017.

page 4 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Welcome

Welcome to the second Joint German-British Liquid Crystal Conference 2017, held in Würzburg (Ger- many). After the first successful conference, we warmly welcome our participants, especially from the United Kingdom, but also all other international guests, to the historically rich city of Würzburg. The conference is held in the Toscana Hall of the Würzburg Residence. The Residence, along with its court gardens, is a Unesco World Heritage site. The construction started in 1720 by famous architect Balthasar Neumann and lasted almost a whole century. The host of the conference is the University of Würzburg. Its first foundation dates back to the year 1402. Since then Würzburg was a place of scientific research and is well known for important discoveries, including X-rays by Wilhelm Conrad von Röntgen (1st Nobel Prize in Physics, 1901) and Sugar Chemistry by Emil Fischer (Nobel Prize in Chemistry, 1902). Therefore, we hope that the conference location will provide the ideal environment for fruitful scientific discussions and the generation of new ideas and new collaborations.

All oral presentations and the poster appetizers are given in the Toscana Hall, on the second floor of the Residence. At the entrance, you will find the registration desk, where we can assist you in any kind of enquiries. A cloakroom is available on the same floor. On the last day of the conference, this room is available to leave your luggage until departure.

Coffee breaks will take place on the third floor. Please note that to prevent damage, it is not allowed to bring drinks or food into the Toscana Hall.

There are plenty of nearby restaurants available for lunch breaks in the city center (walking distance 10-15 minutes), which should give participants plenty of time to be back for the afternoon sessions.

The Poster Session is located in lecture hall 3 on the ground floor. There are two poster sessions: on Mon- day and Tuesday. Please make sure that you put up your poster before 17:00 on Monday, and remove it before 11:00 on Wednesday. For the Monday poster session, all presenters of even-numbered posters are expected to be at their posters, whilst during the Tuesday poster session all presenters of odd-numbered posters should be available for discussion.

Free WiFi is available (Login: gblcc17, Password: gblcc17CC). Alternatively, the Eduroam WiFi system is also available throughout the University of Würzburg.

Thank you for attending the conference. It is your contributions that will make this meeting a great suc- cess! We also express sincere thanks to our sponsors, without whose invaluable support this conference would not have been possible.

A full-colour PDF of these proceedings can be downloaded from our website: http://www.chemie.uni-wuerzburg.de/germanbritishlc2017/programme/ (or use the QR-Code)

Conference Chair Conference Co-Chair Matthias Lehmann Philip Hands

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 5 Programme Monday, April 3rd, 2017

Time Speaker Titel

13:30 - 13:45 Opening Prof. Christoph Lambert Welcome Address by the Dean of the Faculty of Ceremony (Dean of the Faculty) Chemistry and Pharmacy (University of Würzburg) Matthias Lehmann Welcome Address of the Chairs Philip Hands Chair: Matthias Lehmann (University of Würzburg) 13:45 - 14:15 I1 Bertrand Donnio Self-Assembly of Ligand Functionalization Directed CNRS-Université de Nanoparticles (Sturgeon Lecture) Strasbourg 14:20 - 14:40 O1 Tilen Potisk Magneto-optic Dynamics in a Ferromagnetic Nematic University of Bayreuth Liquid Crystal 14:40 - 15:00 O2 Fedor Podgornov Impact of Achiral Gold Nanorods on Chiroptic TU Darmstadt Response of Ferroelectric Liquid Crystal 15:00 - 15:20 O3 Ben Hogan Control and Characterisation of Meta-Structured University of Exeter Liquid Crystalline Nanocomposites as a Platform for Optoelectronic Devices

15:20 - 15:50 Tea/Coffee

Chair: Philip Hands (University of Edinburgh) 15:50 - 16:10 I2 Richard Mandle Liquid-Crystalline, Oligomeric Twist-Bend University of York Nematogens (BLCS Young Scientist Award) 16:10 - 16:30 O4 Chris Welch Extending the Structural Parameters of Systems with University of Hull Two Nematic Phases 16:30 - 16:50 O5 Xiangbing Zeng Molecular Organization in the Twist-Bend Nematic University of Sheffield Phase by Resonant X-ray Scattering at the Se K- Edge and by SAXS, WAXS and GIXRD 16:50 - 17:10 O6 Alexey Eremin Cluster Formation Emergence of Polar Order in University of Magdeburg Hockey-Stick and Bent-Core Liquid Crystals 17:10 - 17:30 O7 Andrew Masters Phase Behaviour of Hard Board-like Particles University of Manchester 17:30 - 17:50 Poster Appetizer

PA1 Ingo Dierking BaTiO3 Nanoparticles in Nematic and Ferroelectric University of Manchester Liquid Crystal Phases PA2 Ingo Dierking Lyotropic Liquid Crystals from Graphene Oxide University of Manchester PA3 Magaret Normand Chiral Nematic Droplets for Lasing: Microfluidic University of Edinburgh Generation and Manipulation PA4 Stefan Maisch Does the Magic Angle promote the Formation of University of Würzburg Nematic Liquid Crystals? PA5 Ethan I. L. Jull Tuneable, Switchable Liquid Crystal Laser Filter University of Leeds PA6 Martin Lambov Hybride Peptide/OPV Star-Mesogens University of Würzburg PA7 Josh Walton Flow of Active Nematics in Confined Geometries University of Strathclyde

17:50 - 18:55 Poster Session (Even-Numbered Posters) Meeting Point at 19:00 h: 19:00 - 22:00 Wine Tasting Fountain in front of the Residence (Frankoniabrunnen, Residenzplatz)

page 6 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Tuesday, April 4th, 2017 Programme

Time Speaker Titel

Chair: Andrew Masters (University of Manchester) 9:00 - 9:30 I3 John Lydon The Identification of Chromonic Mesophases University of Leeds (Gray Medal) 9:30 - 9:50 O8 Doug Cleaver A Twist on Self-Assembly: Hierarchical University of Sheffield Architectures Formed by Amphiphilic Chromonics 9:50 - 10:10 O9 Sarah Gray Studying Lyotropic Mesophases, and the Molecular Durham University Properties that Influence Them, Using Dissipative Particle Dynamics 10:10 - 10:30 O10 Mikhail Osipov On the Theory of Helical Twisting in Lyotropic University of Strathclyde Ferroelectric Liquid Crystals

10:30 - 10:50 Tea/Coffee

Chair: Heiner Detert (University of Mainz) 10:50 - 11:10 O11 Michael Giese A New Perspective of the Structure-Property University Relationships in Hydrogen-bonded Liquid Crystals of Duisburg-Essen 11:10 - 11:30 O12 Tapas Ghosh Donor/Acceptor Porphyrin-TTF/Oligothiophene Star University of Würzburg Dyad: Potential Photovoltaic Materials 11:30 - 11:50 O13 Marco Poppe From X-shaped to Star-Shaped Bolapolyphiles University of Halle 11:50 - 12:10 O14 Stefanie Herbst Development of Novel Liquid Crystalline J- University of Würzburg Aggregates Utilizing Supramolecularly Engineered Perylene Bisimides

12:10 - 14:00 Lunch

Chair: Ingo Dierking (University of Manchester) 14:00 -14:30 I4 Nigel Mottram Cornered (Hilsum Medal) University of Strathclyde 14:30 - 14:50 O15 Clarissa F. Dietrich Observation of Chiral Structures from Achiral University of Stuttgart Micellar Lyotropic Liquid Crystals Under Capillary Confinement 14:50 - 15:10 O16 A. Helen Macaskill Confinement of Microparticles at Defects in a University of Leeds Nematic Liquid Crystal 15:10 - 15:30 O17 Goran Ungar Columnar Liquid Crystals in Cylindrical Confinement University of Sheffield

15:30 - 16:10 Tea/Coffee CONFERENCE PHOTOGRAPH

Chair: Heinz Kitzerow (University of Paderborn) 16:10 - 16:40 I5 Victor Reshetnyak Electrically Tunable Liquid Crystal Lenses University of Kyiv 16:40 - 17:00 O18 Devesh Mistry Designing and Characterising the Soft Elasticity University of Leeds of Acrylate Liquid Crystal Elastomers with Tuneable Physical Properties 17:00 - 17:20 O19 Lukas B. Braun Microfluidic Synthesis of Liquid Crystalline University of Mainz Elastomer Micropumps 17:20 - 17:40 O20 Alexander Lorenz Light Induced Mircomanipulation and Defect University of Paderborn Formation in Nematic Liquid Crystals via Photovoltaic Fields

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 7 Programme Tuesday, April 4th, 2017

17:40 - 17:55 Poster Appetizer PA8 Florian von Rüling Transient Dynamics in the Accelerating Region of University of Magdeburg Collapsing Freely Suspended Films PA9 Joachim Vollbrecht Blends of Two Perylene Derivatives: Liquid University of Paderborn Crystalline and Optoelectronic Properties PA10 David Ditter Microtechnical Processing of Liquid Crystal University of Mainz Elastomers PA11 Tristan Hessberger Co-Flow Microfluidic Synthesis of Liquid Crystalline University of Mainz Actuating Janus Particles PA12 Moritz Dechant Phthalocyanine Hybrid Star Mesogens – New University of Würzburg Materials for Potential Photovoltaic Applications PA13 Heiner Detert Structural Changes upon Heating University of Mainz Tristriazolotriazines

17:50 -18:50 Poster Session (Odd-Numbered Posters) BLCS and DFKG BLCS AGM (Toscana Hall), DFKG AGM (HS1) 18:50 - 20:00 Annual General Meeting B. Neumann Residenzgaststätte, Residenzplatz 1 20:00 - 24:00 Conference Dinner (Residence Place), Schönbornsaal

page 8 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Wednesday April 5th, 2017 Programme

Time Speaker Titel

Chair: Jan Lagerwall (University of Luxembourg) 9:00 - 9:30 I6 Matthias Bremer The Development of Dielectrically Negative Nematic Merck KGaA Darmstadt Liquid Crystals 9:30 - 9:55 O21 Hassan-Ali Hakemi Industrial Development of Plastic Liquid Crystal Gauzy Europe Technology 9:55 - 10:15 O22 Markus Wahle Electrode Patterning by Nanosphere Lithography for University of Paderborn Switchable 2D Blue Phase Gratings 10:15 - 10:35 O23 Sophie Jones Measurement of Homeotropic Surface Anchoring University of Leeds and Slip in Liquid Crystal Displays through Bistable Latching 10:35 - 11:00 Tea/Coffee

Chair: Frank Giesselmann (University of Stuttgart) 11:00 - 11:20 I7 Prize Winner Ceremony Saupe Medal Laudatio of Prof. Dr. Ralf Stannarius (University of Magdeburg) 11:20 - 11:40 O24 Patricia Dähmlow Temporal Shape-Evolution of Freely Floating University of Magdeburg Smectic Bubbles 11:40 - 12:00 O25 Christoph Klopp Microrheology of Rod-Shaped Particles in Freely University of Magdeburg Suspended Liquid Crystal Films 12:00 - 12:20 O26 Fraser Mackay Poiseuille Flow of Exotic Emulsions Containing University of Edinburgh Nematic Liquid Crystals 12:20 - 14:00 Lunch

Chair: Alexander Lorenz (University of Paderborn) 14:00 -14:20 O27 Buddhapriya Chakrabarti Elasticity of Smectic Liquid Crystals with In-Plane University of Sheffield Orientational Order, and Dispiration Asymmetry 14:20 - 14:40 O28 Jürgen Schmidtke Light Emission in Cholesteric Films: Temperature University of Paderborn and Angular Dependence 14:40 - 15:00 O29 Bernhard Atorf Methyl Red Doped Liquid Crystals and Their University of Paderborn Combination with Metamaterials 15:00 - 15:20 O30 Iris Wurzbach Higher Ordered Smectic Liquid Crystals as University of Stuttgart Semiconductors in Organic Field-Effect Transistors 15:20 - 15:40 Frank Giesselmann DFKG Young Scientist Awards BLCS Best Poster and Talk Awards Matthias Lehmann Philip Hands Closing Remarks

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 9 Invited Lectures...... 11 - 16

Oral Lectures...... 17 - 46

Posters...... 47 - 99

page 10 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Self-Assembly Of Ligand Functionalization Directed Nanoparticles Bertrand Donnio* & Jean-Louis Gallani Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS-Université de Strasbourg (UMR 7504), 23 rue du Loess, BP43, 67034 Strasbourg Cedex 2, France Corresponding author e-mail: [email protected]

Self-assembly of nanoparticles (NPs) into designed structures is of relevance for engineering new materials with tuneable and reconfigurable functions, as well as for the subsequent bottom-up fabrication of devices. Such (meta)materials, made from NP assemblies, are able to process incoming EM waves in a manner that is not achievable using regular materials directly built from atoms or molecules. They boast spectacular properties (i.e. negative refraction, magnetism, superlensing, ) and are therefore much sought after for the design of innovative applications. Of importance, the collective properties of such assemblies are crucially influenced by the surface functionalization (ligand shell). We recently developed bottom-up chemical routes for the preparation of such hybrids. With the help of some examples, we will show how the ligand shell affects both self-assemblies and certain physical properties. Dendritic ligands of several generations tethered to the surface of NPs allow the control of their assemblies into 2/3D lattices, whereas the change in the dendritic generation allows a precise control of NP separation. This offers potential for optimising collective responses for applications including optical and magnetic. Dual mixing of dendronized species further produces unprecedented binary superlattices, whose properties are intrinsically modulated at nm-scale distances. Hydrophobic colloidal NPs are mainly synthesized and manipulated with commercially available ligands. These remain invaluable but surface functionalization is typically limited to a small number of molecules. We have recently proposed a robust method using polycatenar ligands for the direct synthesis of a wide variety of monodisperse (e.g. metallic, chalcogenide, pnictide, and oxide) NPs. Self- assembly into single component and binary NP superlattices (BNSLs) demonstrates the excellent monodispersity of the produced NPs. In addition, some NPs self-assemble into bcc superlattices that deviate from conventional close-packed structures (fcc or hcp) formed by the same NPs coated with commercial ligands. The thorough study demonstrates that the molecular structure of the polycatenar ligands encodes interparticle spacings and specific attractions, engineering self-assembly, which is tuneable from hard sphere to soft sphere behaviour. Polycatenar and dendritic molecules (mesomorphous or not) thus offer versatile modular platforms for the development of ligands with targeted properties, bringing organic functionality to inorganic NCs. This subsequently controls aspects such as solubility, interparticle spacings, self- assembly, liquid crystalline behaviour and physical properties. It is expected that structural complexities and practical utilities be achieved through a thoughtful exploitation of organic chemistry and expanded to various inorganic systems.

References [1] D. Jishkariani, et al. J. Am. Chem. Soc. 2015 137 1072810734. [2] B. T. Diroll, et al. J. Am. Chem. Soc. 2016 138 10508-10515. [3] S. Fleutot, et al. Nanoscale 2013 5 15071516. [4] B. Donnio, et al. Adv. Mater. 2007 19 35343539. [5] L. Malassis, et al. Nanoscale 2016 8 13192-13198.

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 11 Liquid-Crystalline, Oligomeric Twist-Bend Nematogens Richard J. Mandle 1 1The University of York, York, UK Corresponding author e-mail: [email protected]

The twist-bend nematic phase (NTB) exhibited by LC dimers is a something of a fairly well established phenomenon, and the number of materials known to exhibit this phase has grown

significantly since its discovery. [1] The experimental observation of a linear relationship between TNTB-N

and TN-ISO indicates that the NTB phase is primarily a product of molecular shape, and that this phase is likely to manifest on length scales beyond those of dimers. [2]

Plots of the TNTB-N versus the TN-ISO for dimers, bimesogens and oligomers with (a) heptamethylene spacers and (b) nonamethylene spacers.

As understanding of this phase in simple dimers has grown our attention (as synthetic chemists) has

shifted to oligomeric materials that exhibit the NTB phase. While the preparation of trimer and tetramer type systems is chemically trivial [3, 4] the synthesis of monodisperse higher oligomers is a much more challenging proposition. In response to this we have developed a step-wise synthetic approach that has

allowed us to obtain perfectly monodisperse hexametric LC materials that exhibit the NTB phase. [5]

References [1] R. J. Mandle, Soft Matter, 2016, 12, 7883-7901 [2] R. J. Mandle and J. W. Goodby, Chem. Eur. J., 2016, 51, 18456–18464 [3] R. J. Mandle and J. W. Goodby, ChemPhysChem, 2016, 17,967-970 [4] R. J. Mandle and J. W. Goodby, RSC Adv., 2016, 6, 34885-34893 [5] F. P. Simpson, R. J. Mandle, J. N. Moore and J. W. Goodby, manuscript submitted, 2017

The Identification of Chromonic Mesophases

John E Lydon

Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK Corresponding author e-mail: [email protected]

I + M(ribbons)

Sodium dicromoglycate

100 m

Chromonic mesophases had to wait a long time to be identified. The realisation that there was a second distinct family of lyotropic phases could have emerged decades earlier - from studies of dyes or nucleic acids. However it came from a study of a drug - and even then, for a long time it was taken that chromonic phase formation was a unique property of a unique compound. This talk will describe the context of the early study of the mesophases formed by aqueous solutions of the anti-asthmatic drug disodium cromoglycate (variously known as INTAL or Cromolyn). The previous work of Norman Hartshorne and the McCrone Research Institute (in London) will be described and the various tentative models for the two chromonic mesophases discussed. Solving the structures involved fitting together a jigsaw of pieces of evidence - the molecular structure, the rich pattern of optical textures, the optical signs of the mesophases, X-ray diffraction patterns and the form of the phase diagram - all of which were unfamiliar in liquid crystal work of that time. At first the idea that there could have been a large, previously unidentified family of lyotropic mesophases was widely regarded as preposterous. And it was to be almost twenty years before the use of the term ‘chromonic’ became generally accepted. In retrospect, it was merely a matter of being in the right place at the right time, with the right background knowledge – and being fortunate enough to have talented colleagues to work with. I acknowledge the key work of my colleagues; Theresa Attwood, Jane Turner and John Bunning – and the help and advice I have received, then and subsequently, from Gordon Tiddy and George Gray.

References [1] J Lydon, Liquid Crystals, 2011 38:11-12, 1663-1681, DOI: 10.1080/02678292.2011.614720 Cornered

Nigel Mottram

Department of Mathematics & Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, UK Corresponding author e-mail: [email protected]

All liquid crystal devices involve some form of confinement, usually between two parallel glass plates. Indeed, it is the forces and torques due to the orienting effects of bounding surfaces and their competition with other influences such as elastic and electric fields that lead to many interesting and useful liquid crystal phenomena. While most experimental liquid crystal devices involve planar bounding surfaces, commercial liquid crystal displays often include electronics which make the bounding surface non-planar and recent fundamental research has considered non-planar surfaces, for instance as a mechanism to induce bistability. In this talk I will consider the role that a specific aspect of confinement, the corners of a boundary, have to play in liquid crystal systems. It has been known for a number of years that corners can add stability and robustness to delicate director configurations, sometimes introducing defects into regions close to corners, and sufficiently strong anchoring near to corners can lead to multistability (see Figure below). Mathematical analysis and prediction for such strongly anchored systems can be difficult because defects lead to singularities in the director configuration, necessitating the use of nonlinear models such as the Landau-de Gennes Q-tensor approach. However, even for strong anchoring some analysis is possible, with good agreement to experiments, and when weaker anchoring is concerned theory predicts the presence of “virtual” defects with the resulting director structure have a smaller region of stability but with a greater ability to switch between states. Conversely, in systems where rounded corners are often used (the extreme example being defects wrapped around spheres) such corners may enhance the stability of a configuration.

Multistable states for a variety of different corner configurations: experiment (rows 1 and 3) and experiments (rows 2 and 4) [1]

References [1] C.R. Evans et al. J. Phys. D: Appl. Phys. 2010 43 art. no. 495105 Electrically Tunable Liquid Crystal Lenses

Victor Reshetnyak

Physics Faculty, Taras Shevchenko National University of Kyiv, 64 Volodymyrska Street, 01601, Kyiv, Ukraine Corresponding author e-mail: [email protected]

Liquid crystals (LC) are widely used in many optical devices and in many applications, for instance in displays, light modulators and deflectors, beam couplers, etc. In recent years there has been much interest in active optical elements, e.g. lenses with variable focal length [1, 2]. In this talk I briefly review mechanically, electrically and magnetically tunable liquid and liquid crystal lenses. Some examples of electrically tunable LC lenses include lenses with flat, curved and floating electrodes. It will be presented theoretical modelling for three types of liquid crystal lenses: i) lens that uses a combination of two dielectric lenses and voltage dividing principle to shape the electric field in space [3]; ii) tunable LC contact lens [4] and iii) polarization insensitive multilayer LC lens with high resistive layer [5]. In all modellings the electric field, LC reorientation, and optical phase retardation profiles are found by numerical simulations. The modelling results are compared to the experimental ones.

References [1] Hongwen Ren and Shin-Tson WU Introduction to Adaptive Lenses, 2012, Wiley series in pure and applied optics. [2] Nam-Trung Nguyen Micro Optofluidic Lenses - a Review, Biomicrofluidics, 2010, 4, 031501 [3] Oleksandr Sova, Victor Reshetnyak, Tigran Galstian and Karen Asatryan, “Electrically variable liquid crystal lens based on the dielectric dividing principle”, JOSA A, 2015, 32, 803-808. [4] H. E. Milton, P. B. Morgan, J. H. Clamp, and H. F. Gleeson, "Electronic liquid crystal contact lenses for the correction of presbyopia," Opt Express, 2014, 22, 8035-8040. [5] H. S. Chen, Y. J. Wang, C. M. Chang, and Y. H. Lin, “A polarizer-free liquid ... embedded- multilayered structure, IEEE Photonic Technol. Lett., 2015, 27, 899-902. The Development of Dielectrically Negative Nematic Liquid Crystals

Matthias Bremer Merck KGaA – Performance Materials Liquid Crystals Frankfurterstr. 250, D-64293 Darmstadt, Germany Corresponding author e-mail: [email protected]

The role of dielectrically negative nematic liquid crystals (LCs) in the development of flat panel display technology can hardly be overestimated.[1] Vertically aligned LCs were crucial for the realization of desktop monitors in the late 1990s and television sets from the early 2000s on. Very recently negative materials have also been used to improve the performance of displays in portable devices such as smart phones and tablet computers.[2]

The history of the corresponding material development will be briefly outlined. State-of-the-art compounds will be presented with structure-property data. Examples of failed and successful design strategies towards improved liquid crystals will be discussed.

X-Ray crystal structure of a 2-tetrahydropyranyl-1,1,6,7-tetrafluoroindane

References [1] M. Bremer, P. Kirsch, M. Klasen-Memmer, K. Tarumi, "The TV in Your Pocket: Development of Liquid-Crystal Materials for the New Millennium", Angew. Chem. Int. Ed. 2013, 52, 8880-8896. [2] M. Engel, G. Bernatz, A. Goetz, H. Hirschmann, S.-K. Lee, “UB-FFS: New Materials for Advanced Mobile Applications”, Digest of Technical Papers – Society of Information Display Symposium 2015, 46, 645-647.

Magneto-optic Dynamics in a Ferromagnetic Nematic Liquid Crystal

T. Potisk1,2,*, N. Sebastián3, D. Lisjak3, A. Mertelj3, H. Pleiner4, H. R. Brand2, D. Svenšek1

1Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, Slovenia 2Department of Physics, University of Bayreuth, 95440 Bayreuth, Germany 3J. Stefan Institute, SI-1000 Ljubljana, Slovenia 4Max Planck Institute for Polymer Research, 55021 Mainz, Germany E-mail: [email protected]

It has long been known that by dispersing ferromagnetic nanoparticles in a nematic liquid crystal one could induce a ferromagnetic liquid crystal phase.[1] Only recently this phase was successfully experimentally realized.[2] Unlike for usual nematics, the ferromagnetic phase is sensitive to very small magnetic fields and could be used in various magneto-optic devices.[3] We model the dynamics of ferromagnetic nematics using the existing theory.[4] As a first step, we take as relevant macroscopic variables only the director field and the magnetization with its magnitude only slightly departing from its equilibrium value.

Figure 1: Fit of the measured time dependence of the Figure 2: Fit of the measured time dependence of the normalized phase difference with the model for µ0H = normalized phase difference with the model after switching

7 mT. off the field of strength µ0H = 7 mT.

In experiments a ferromagnetic nematic sample is put between two glass plates approximately 20 µm apart.[3] A magnetic field of strength of the order of mT is applied perpendicularly to the glass plates and the phase difference of the transmitted light is measured. We model the dynamics of this phase difference numerically taking into account dissipative and reversible currents. It turns out that the dissipative cross-currents are crucial for the explanation of the experimental data. We study the relaxation rate of the switching process. Using sufficiently high values of the dissipative cross-coupling coefficient we obtain a linear dependence of the relaxation rate on the applied magnetic field as is observed in experiments. Furthermore we study the relaxation rate when the system is allowed to relax from a state obtained by switching on a magnetic field. The relaxation rate saturates at a finite value for very high initial magnetic fields in agreement with the experiments.

We thank the DFG for partial support through the Priority program 1681.

References [1] F. Brochard and P. G. de Gennes, Journal de Physique 1970, 31, 691-708. [2] A. Mertelj, D. Lisjak, M. Drofenik and M. Čopič, Nature 2013, 504, 237-241. [3] A. Mertelj, N. Osterman, D. Lisjak and M. Čopič, Soft Matter 2014, 10, 9065-9072. [4] E. Jarkova, H. Pleiner, H.-W. Müller, H. R. Brand, J. Chem. Phys. 2003, 118, 2422-2430 Impact of Achiral Gold Nanorods on Chiroptic Response of Ferroelectric Liquid Crystal

Fedor Podgornov1,2) *, Zbigniew Tomkowicz3, Wolfgang Haase1,2

1)Eduard Zintl Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Alarich Weissstr. D-64287, Darmstadt, Germany 2)Laboratory of Molecular Electronics, South Ural State University, Chelyabinsk, Lenin ave. 76, 454080, Chelyabinsk, Russia 3)Institute of Physics, Jagiellonian University, Reymonta str. 4, 30059, Krakow, Poland *E-mail: [email protected]

Ferroelectric liquid crystals or ferroelectric liquid crystals (FLC) are usually multicomponent mixtures consisting of an achiral matrix and a chiral component. Because of their helical superstructure, homeotropically aligned FLC cells demonstrate resonance scattering (Bragg reflection band) of electromagnetic radiation (Fig.1a) visible in the circular dichroism (CD) spectrum. In this report we will experimentally demonstrate that the incorporation of the achiral gold nanorods (GNRs) possessing the localized surface plasmon resonance (LSPR) in the structure of FLC leads to modification of the chiroptic response (CD spectrum) of FLC.

a b

c d

Figure1: CD spectrum of pristine FLC(a), CD spectra of FLC/GNRs dispersion with concentration 0.1 % wt. (b) and 0.5 % wt. (c), Interaction of a gold nanorod with a chiral molecule (d).

Moreover, the CD response of FLC/GNRs is a function of the GNRs concentration (0.1% wt. and 0.5 % wt.)

These effects will be explained by contribution two phenomenon. The first one is the influence of the FLC’s chiral component on the nanoparticles (induction of chiral current) leading the CD line near the LSPR wavelength. The second effect is changing angle between electric and magnetic transitional dipole moments of the chiral component by LSPR, which results in modification of the CD spectrum of the sample near the absorption lines of the chiral components of FLC mixture (Fig.1d).

Control and Characterisation of Meta-Structured Liquid Crystalline Nanocomposites as a Platform for Optoelectronic Devices

Ben Hogan1*, Tatiana Perova2,3, Sergey Dyakov4, Samuel Rault1,5, Jenny O'Dowd1, Yuri Gun’ko3,6, Monica Craciun1 and Anna Baldycheva1†.

1 University of Exeter, College of Engineering Mathematics and Physical Sciences, Exeter, EX4 4QF, UK 2 Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Ireland 3 ITMO University, 49 Kronverkskiy pr., St.-Petersburg, 197101, Russia 4 Skolkovo Institute of Science and Technology, Photonics and Quantum Material Center, Nobel street 3, Moscow, Russia 5 École Nationale Supérieure de Mécanique et des Microtechniques, Besançon, France 6 School of Chemistry, Trinity College, The University of Dublin, Dublin 2, Ireland * [email protected] † [email protected]

Liquid crystalline nanocomposite materials are a novel class of hybrid fluid materials, which are currently attracting significant interest from the optoelectronics community due to their unique capability to interact with light, utilising many possibilities in plasmonics and quantum optics. Such nanocomposites are based on low-dimensional nanoparticles (carbon nanotubes, graphene, transition metal dichalcogenides (TMDCs), metal nanoparticles etc.) dispersed in a fluidic host material. Liquid crystalline properties can be accessed either by using a commercial nematic liquid crystal host fluid, or, through the solvent-induced self-assembly of particles. The nanocomposites can be readily integrated on silicon chip by means of microfluidic technology allowing for dynamic control of the dispersed particles through the application of various on-chip stimuli. In this paper, liquid crystalline nanocomposites have been synthesised based on two- dimensional (2D) materials including graphene oxide (GO) and TMDCs dispersed in either commercially available liquid crystals or various organic solvents. Here, we present our first results on the formation of metastructures using novel liquid crystalline composites and suitable design of chips or cells to allow dynamic application of aligning fields. As part of this work, we have also developed a novel characterisation tool- based on Raman spectroscopy- to monitor the on-chip self-assembly of nanoparticle metastructures based on highly accurate monitoring of the spatial dynamics of individual nanoparticles in three dimensions, and consider how effective chip design can facilitate this process. We also consider how the inclusion of these materials can be used to modify the properties of the host liquid; in particular, enhancing or suppressing the circular dichroism signal and affecting the switching times under applied stimuli. Extending the Structural Parameters of Systems with Two Nematic Phases

Chris Welch, Ziauddin Ahmed, Efthymia Ramou, Georg H. Mehl*

Department of Chemistry, University of Hull, Hull HU6 7RX, UK E.Mail: c.weclch,@hull.ac.uk, [email protected]

Recently thermotropic LC materials which exhibit two consecutive nematic phases have attracted considerable attention.[1-4] The low temperature (second) nematic phase, forming via a first or second order transition and characterized by the spontaneous formation of chiral domains in non-chiral compounds has been of particular interest. The correlation between molecular structure and the nematic - nematic phase transitions (N-Nx/tb) is not yet fully understood and indeed the structural parameters defining the low temperature nematic phase and the impact on its properties are still being explored, though a number of additional models,based on new experimental data have recently been proposed.[4] Here we will present results on sets of new materials and mixtures designed with the specific aim of understanding the phase structure and properties of the low temperature nematic phase better. We present here the design and synthesis of a number of systems based around fluorinated terphenyl and cyanobiphenyl units linked by flexible alkyl spacers of both odd and even lengths and mixtures thereof. The chemistry has been controlled in such a way as to give symmetric and non- symmetric oligomeric systems, both in terms of the aromatic mesogens and the alkyl spacers. The synthesis and characterisation of these materials by OPM, DSC and detailed, temperature dependent XRD studies will be presented and compared to the known dimers.[1b, 1h, 3c, 4d] Mixtures of these oligomers with the relevant dimers and other mesogens in the nematic and Nx/tb phases will be described and the resulting phase behaviour discussed.

References [1] V. P. Panov et al., Phys. Rev. Lett., 2010, 105, 167801; (b) V. Borshch et al., Nat. Commun. 2013, 4, 26351; (c) D. Chen et al., Proc. Natl. Acad. Sci. U.S.A., 2013, 110, 15931; (d) L. Beguin et al., J. Phys. Chem. B, 2012, 116, 7940; (e) V.P. Panov et al., Appl. Phys. Lett., 2012, 101, 2341061; (f) C. Meyer et al., Phys. Rev. Lett. 2013, 111, 067801; (g) A. Hoffmann et al., Soft Matter, 2015, 11, 850; (h) M.- G. Tamba et al., RSC Advances, 2014, 5, 11207; (i) E. Gorecka et al., Liq. Cryst., 2015,42, 1. [2] C.S.P. Tripathi et al., Phys. Rev. E, 2011, 84, 0417071; (b) R. J. Mandle et al., Phys. Chem Chem. Phys. 2014, 16, 6907; (c) S. M. Jansze et al., Angew. Chem. Int. Ed. 2015, 54, 643 [3] G. Ungar et al., Polym. Bull., 1994, 32, 325; (b) M.Šepelj et al., J. Mater. Chem. 2006, 16, 1154; (c) Z. Ahmed et al. RSC Advances, 2015, 5, 93513. [4] R. J. Mandle, Sci Rep. 2016, 6, 36682; (b) C. Zhu et al, Phys. Rev. Lett. , 2016, 116, 147803; (c) J. P. Abberley, Liq. Cryst. 2017, DOI:10.1080/02678292.2016.1275303; (d) S. M. Salili et al., Phys. Rev. Lett. 2016, 116, 217801.

Molecular Organization in the Twist-Bend Nematic Phase by Resonant X-Ray Scattering at the Se K-edge and by SAXS, WAXS and GIXRD

1 2 1,* 2 1,3 2 W. D. Stevenson , Z. Ahmed , X. B. Zeng , C. Welch , G. Ungar and G. H. Mehl

1Department of Materials Science and Engineering, University of Sheffield, UK 2Department of Chemistry, University of Hull, UK 3Department of Physics, Zhejiang Sci-Tech University, China E-mail: [email protected]

The investigation of the new LC phase termed twist-bend nematic (Ntb) has in the last few years arguably become the most pressing issue in liquid crystal research, as its understanding tests the current limits of theoretical models and LC phase analysis. The heliconical model of this phase has gained strong experimental support e.g. from Cryo-TEM [1,2], and more recently from resonant X-ray scattering at the carbon absorption edge (K-edge) [3]. Using a novel Se-labelled dimer mixed with the terphenyl dimer DTC5C7, we studied the Ntb phase by hard X-ray resonant scattering at the Se-edge. This allowed us to overcome the limitations of experimentation with soft X-rays, such as substrate effects and lack of orientation. As in [3], we observed resonant diffraction, indicating a helix with a 9-12 nm pitch in the Ntb phase and confirming the heliconical structure of the Ntb phase. In addition, the use of hard X-ray enabled us to align the sample with a magnetic field, which revealed surprisingly high, virtually perfect orientation of the helical axis (Fig. 1a). This, combined with simultaneous resonant and non-resonant SAXS and WAXS data, allowed us to construct a model of the Ntb phase with more quantitative details, e.g. matching twisted molecular conformations and the local heliconical director field (Fig. 1b).

Figure 1. (a) Surface plot of the SAXS diffractogram of the Ntb phase aligned in magnetic field, recorded at the Se-K edge (12.658 keV). Note the perfect orientational order of the resonance peak with corresponding d-spacing of 12.1 nm. (b) Ntb phase assembled from molecules with conformations approximated by helical segments.

References [1] V. Borshch,Y.-K. Kim, J. Xiang, M. Gao, A. Jakli, V. P. Panov, J. K. Vij, C. T. Imrie, M. G. Tamba, [2] G. H. Mehl, O. D. Lavrentovich. A. Nat. Commun. 2013, 4, 2635. [3] D. Chen, J. H. Porada, J. B. Hooper, A. Klittnick, Y. Shen, M. R.Tuchband, E. Korblova, D. Bedrov, [4] D. M.Walba, M. A. Glaser, J. E. Maclennan, and N. A. Clark. Proc. Natl. Acad. Sci. U.S.A., 2013, 110, 15931. [5] C. Zhu, M. R. Tuchband, A. Young, M. Shuai, A. Scarbrough, D. M. Walba, J. E. Maclennan, C.Wang, A. Hexemer, N. A. Clark. Phy. Rev. Lett, 2016, 116, 147803.

Cluster Formation Emergence of Polar Order in Hockey-Stick and Bent-Core Liquid Crystals

Alexey Eremin1, Mohamed Alaasar2,3, Carsten Tschierske2 1Institute of Experimental Physics, Otto von Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg 2Institute of Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes Str. 2, 06120 Halle 3Department of Chemistry, Faculty of Science, Cairo University, P.O. 12613 – Giza, Egypt

Formation of cybotactic and polar clusters liquid crystalline states results in unusual and very interesting properties of liquid crystalline phases. Is has been shown that the cybotactic clusters are responsible for an anomaly of the bend elastic constant and the polar clusters can be responsible for a strong flexoelectric in some bent-core compounds [1-3]. In our research, we investigate the formation of the polar order in 4-cyanoresorcinol derived bent- and hockey-stick compounds. The hockey-stick mesogens exhibit a variety of skewed and non-skewed cybotactic nematic phase. Using dielectric spectroscopy under bias field, we demonstrate a field-induced induction of a slow relaxation mode which can be attributed to the formation of the polar custers. In the bent-core compound, polar phases condense from a series of phases with randomised polarisation. Using nonlinear optics and dielectric spectroscopy, we show a transition from a phase forming randomised polar clusters into an orthogonal phase with clusters exhibiting antipolar correlations [4].

References [1] S. Aya et al., Adv Mater, 26, 12, 1918–1922, (2014). [2] S. P. Sreenilayam et al., Nature Comm. 92, 2, 022502, (2015). [3] S. H. Hong, Soft Matter, 6, 19, 4819–4827, (2010). [4] N. Sebastián et al, PCCP, accepted (2017)

Phase Behaviour of Hard Board-like Particles

Alessandro Patti*,1, Matthew Dennison2 , Andrew Masters1 , Alejandro Cuetos3

1School of Chemical Engineering and Analytical Science, University of Manchester, Manchester, M13 9PL, UK 2Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstrasse 36,10623 Berlin, Germany 3Department of Physical, Chemical and Natural Systems, Pablo de Olavide University, 41013 Sevilla, Spain E-mail: [email protected]

We examine the phase behaviour of colloidal suspensions of hard board-like particles (HBPs) as a function of their shape anisotropy, and observe a fascinating spectrum of nematic, smectic and columnar liquid-crystalline phases, whose formation is entirely driven by excluded volume effects. We map out the phase diagram of short and long HBPs by gradually modifying their shape from prolate to oblate and investigate the long-range order of the resulting morphologies along the phase directors and perpendicularly to them. The intrinsic biaxial nature of these particles promotes the formation of translationally ordered biaxial phases, but does not show solid evidence that it would, per se, promote the formation of the biaxial nematic phase. Our simulations shed light on the controversial existence of the discotic smectic phase, whose layers are as thick as the minor particle dimension, which is stable in a relatively large portion of our phase diagrams. Additionally, we modify the Onsager theory to describe the isotropic-nematic phase transition of freely rotating biaxial particles as a function of the particle width, and find a relatively strong first-order signature, in excellent agreement with our simulations. In an attempt to shed light on the elusive formation of the biaxial nematic phase, we apply this theory to predict the uniaxial-biaxial nematic phase transition and confirm, again in agreement with simulations, the prevailing stability of the translationally ordered smectic phase over the orientationally ordered biaxial nematic phase.

Front and top views of biaxial (a) and oblate (b) smectic liquid crystals containing 2000 HBPs. The colour gradient follows the orientation of the particle major axis. A Twist on Self-Assembly: Hierarchical Architectures Formed by Amphiphilic Chromonics

Doug Cleaver*1, Alireza Dastan1, William J Frith2, and Sabetta Matsumoto3

1 Materials and Engineering Research Inst., Sheffield Hallam University, Howard Street, S1 1WB, Sheffield, UK 2 Unilever Research and Development Colworth, Sharnbrook, MK44 1LQ, UK 3School of Physics, Georgia Institute of Technology, North Avenue, Atlanta, GA 30332, USA E-mail: [email protected]

The spontaneous chiral symmetry breaking responsible for many liquid crystalline textures is founded on the intermolecular geometry of bananas, pears and other more complex interaction centres. Likewise, self-assembly into complex structures, ranging from giant unilamellar vesicles to gyroids, is achieved when amphiphiles exploit the chemistry of local immiscibility. Here, we use molecular dynamics simulation to examine new bitartite systems which combine the thread-like aggregation of chromonics with the frustrations of amphiphilicity to yield a range of self-assembled structures with emergent supramolecular chirality. In our simulations, we decorate chromonic discotic particles with a range of solvophylic interactions. Through this, we find that a veritable zoo of hierarchical, chiral self-assembled structures are formed. Simply by tuning the extent of the solvophylic regions and the particle shapes, the morphology of these meso-structures changes from double-helices to twisted bilayers, multi-strand ropes and tubules. As well as observing how these structures initiate and grow, we also use a unified minimal model based upon anisotropic elasticity to explore their stability and limiting behaviours.

Double-helix (top left), multi-strand rope (bottom left) and twisted bilayer (right) structures, freely self-assembled from mixtures of disc-shaped and spherical particles.

Studying Lyotropic Mesophases, and the Molecular Properties that Influence them, using Dissipative Particle Dynamics

Sarah Gray*, Martin Walker, and Mark R. Wilson

Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK

E-mail: [email protected]

Lyotropic liquid crystals are present in a huge number of everyday household items, with the global market worth an estimated $44 billion by 2020. Despite their ubiquity, and the critical role mesophases play in formulations, phase diagrams of complex mixtures remain challenging to predict. Simulation is a powerful tool in elucidating the mechanisms and molecular characteristics that are involved in mesophase formation and stability. Here we present our work using the Dissipative Particle Dynamics (DPD) simulation technique to probe the phase of the common anionic surfactants sodium dodecyl sulfate, SDS, and linear alkylbenzene sulfonates, LAS DPD is a mesoscale method, describing liquid phases on the order of micrometres and milliseconds. A defining feature of DPD is its very soft and purely repulsive inter-particle interaction, quite in contrast to the typically used Lennard-Jones interaction. This allows for longer time and lengths scales to be accessed in comparison to conventional simulations. We present a new DPD model for SDS in water. We find our model readily describes not only the behaviour of SDS across a wide range of concentrations, 5-95 wt%, but is easily extended to represent LAS in water. While our models are in good agreement with the experimental phase diagrams, we find some discrepancies within concentration regions which are particularly difficult to study due to high viscosity. We believe our simulations can give additional insight into the nature of the mesophases present, and also the molecular level behaviours and properties that give rise to them.

Figure showing simulation snapshots of common lyotropic mesophases, and their respective g(r‖ ,rꓕ)s On the Theory of Helical Twisting in Lyotropic Ferroelectric Liquid Crystals

Mikhail A. Osipov1, Johanna R. Bruckner2 and Frank Giesselmann2

1Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, Richmond Street, Glasgow, Scotland, UK 2TInstitute of Physical Chemistry, University of Stuttgart, Stuttgart Germany E-mail: [email protected]

Recently ferroelectric ordering and macroscopic helical twisting have been discovered in the tilted lamellae phase which is the lyotropic analog of the well-known thermotropic ferroelectric SmC* liquid crystal phase [1-3]. It has been found that the correlation of the director tilt orientation in different layers as well as its helical precession occurs via a strong, three-dimensional hydrogen bond network formed by the solvent molecules. At the same time the concentration dependence of the helical pitch is counterintuitive as the pitch decreases with the increasing solvent concentration even though the separation between neighboring layers also increases.

A molecular theory of the helical twisting power in the lyotropic ferroelectric phase has been developed taking into consideration the effective elasticity of the H-bond network. It is shown that the unusual concentration dependence of the helical pitch may be determined by a balance between the so-called piezoelectric contribution, which determines the spontaneous polarization in a single layer, and the flexoelectric contribution which describes \a relationship between the twist deformation and the spontaneous polarization. The two contributions in in the lyotropic ferroelectric phase possess opposite signs and as a result the effective twisting power increases with the increasing solvent concentration due to a decrease of the effective tilt angle.

References [1] J.R. Bruckner, D. Krueerke, J.H. Porada, S. Jagiella, D. Blunk and F. Giesselmann, J Mater. Chem 22, 18198 (2012) [2] J.R. Bruckner, J. H. Porada, C.F. Dietrich, I. Dierking and F. Giesselmann, Angewandte Chemie Intern. Edition 52, 8934 (2013) [3] J.R. Bruckner, F. Knecht, F. Giesselmann, ChemPhysChem, 17, 86 (2016)

A New Perspective of the Structure-Property Relationships in Hydrogen-Bonded Liquid Crystals

Michael Giese*, Michael Pfletscher, Matthias Spengler Michael Giese, University of Duisburg-Essen, Institute of Organic Chemistry E-mail: [email protected]

Supramolecular Chemistry has turned into a powerful tool for the design and processing of new functional materials. Especially hydrogen-bonding has been widely used to obtain “smart materials” such as hydro-gels, polymers or liquid crystals.[1] However, in many cases the details of the complex interplay of intermolecular forces and the resulting structure-property relationships remain obscure. Here, we report on the structural impact of hydrogen-bond donor moieties on the liquid crystalline behaviour of hydrogen-bonded assemblies.[2] The present study is accompanied by a series of highly relevant crystal structures, which allow to correlate the differences in the liquid crystalline behaviours with structural features of the hydrogen-bonded assemblies in the solid state providing the opportunity to derive design principles for novel functional materials.

Representative crystal packing of HQ, RE, CA and PHG assemblies (A - D, upper images) and the observation under cross polarized microscope (below images) show the correlation between structural morphology and thermal behaviour of the investigated hydrogen-bonded assemblies.

References

[1] D. Philp, J. F. Stoddart, Angew. Chem. Int. Ed. 1996, 35, 1154-1196. [2] M. Pfletscher, C. Wölper, Jochen S. Gutmann, M. Mezger, M. Giese, Chem. Commun. 2016, 52, 8549-8552 Donor/Acceptor Porphyrin-TTF/Oligothiophene Star Dyad: Potential Photovoltaic Materials

Tapas Ghosh1, Matthias Lehmann1*

1University of Würzburg, Institute of Organic Chemistry, Am Hubland, 97074 Würzburg, Germany E-mail: [email protected]

Star-shaped shape-persistent molecules allow a rational design of mesogens incorporating different chromophores in the arms and the core and are known for their excellent film forming properties.[1] Recently, shape-persistent stars with an oligo(phenylenevinylene) scaffold (OPV) have been prepared, which create void that can be filled with various guests.[2] An OPV/Fullerene system exhibited a nanosegregated donor-acceptor morphology with a remarkable increase in the mesophase stability.[3] Such nanomorphologies are of general interest for bulk-heterojunction (BHJ) materials and thus, for photovoltaic applications.

In the present work TTF and oligothiophene building blocks have been chosen as electron donors since they are well known semiconductors but are not as photo sensitive as OPV.[4,5] They are attached to a porphyrin core in order to create spacial nanosegregated donors and acceptors (Scheme 1). The thermotropic behaviour and bulk mesomorphic structures are investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and wide- and small-angle X-ray scattering (WAXS, SAXS). The complex morphology will be visualised by molecular modelling and the structures will be confirmed by X-ray fibre scattering simulation, in order to achieve a profound understanding of the structure-property relationship.

References [1] S. A. Ponomarenko, Y. N. Luponosov, J. Min, A. N. Solodukhin, N. M. Surin, M. A. Shcherbina, S. N. Chvalun, T. Ameri and C. Brabec, Faraday Discuss. 2014, 174, 313. [2] (a) P. Maier, M. Grüne, M. Lehmann, Chem. Eur. J. 2016, DOI 10.1002/chem.201604505. (b) M. Lehmann, P. Maier, M. Grüne, M. Hügel, Chem. Eur. J. 2016, DOI 10.1002/chem.201603611. [3] M. Lehmann, M. Hügel, Angew. Chem. Int. Ed. 2015, 54, 4110. [4] T. Yasuda, H. Ooi, J. Morita, Y. Akama, K. Minoura, M. Funahashi, T. Shimomura, T. Kato, Adv. Funct. Mater. 2009, 19, 411. [5] K. V. Rao, K. Jalani, K. Jayaramulu, U. Mogera, T. K. Maji, S. J. George, Asian J. Org. Chem. 2014, 3, 161.

From X-Shaped to Star-Shaped Bolapolyphiles

1 1 1 2 1* Marco Poppe , Marko Prehm , Silvio Poppe , Feng Liu and Carsten Tschierske 1Department of Chemistry, Martin-Luther-University Halle-Wittenberg, Kurt-Mothes- Str. 2, 06120 Halle (Saale), Germany 2Xi’an Jiaotong University, Xi’an 710049, P.R. China E-mail: [email protected]

X-shaped bolapolyphiles consisting of a rigid core, two flexible lateral alkyl chains and a polar head group at each end of the rigid core arose interest as they form a series of complex thermotropic LC phases representing fluid honeycomb structures [1,2]. Herein we report a new series of oligo(phenylene ethynylene) based bolaamphiphiles, having two linear lateral alkyl chains (X-shaped) or two branched lateral alkyl chains at opposite sides (6-star-shaped). The synthesis of the com- pounds is based on a sequence of Sonogashira cross coupling and etherification re- actions. The thermotropic LC phases of these compounds were characterised by po- larizing optical microscopy, DSC and X-ray diffraction. Depending on the type of alkyl chains, whether linear, symmetric branched (n = q, m = p, n ≠ m) or non symmetric branched (n = m, q = p, n ≠ p), these com- pounds show different complex liquid crystalline phases [3]. In our case the mesophase behaviour completely change from the X-shaped (linear n-alkyl chains) to the star-shaped molecules with branched alkyl chains though having the same chain volume. Honeycomb-like LC phases with triangular or square structure were found for star-shaped molecules with nearly identical alkyl chain lengths m, n, p and q (Fig. 1). A large difference between the alkyl chain lengths leads to new LC phas- es. Cubic phases with Pm3n-space group and a new giant hexagonal phase with p6mm-symmetry (consisting of dodecagonal supertiles composed of triangular and square cylinders) were found. Remarkably, a square honeycomb-like structure with p4mm-symmetry occurs at lower temperature below the mesophases involving trian- gular cells. This apparent thermal shrinkage is due the emergence of a tilted organi- zation of the molecules, leading to a smaller cross sectional area of the square cylin- ders. The tilt in adjacent walls is either synclinic or anticlinic which leads to square honeycombs composed of a mixture of racemic helical or achiral cylinders.

Figures 1: General structure of the synthesised bolapolyphilic molecules.

References [1] C. Tschierske, Angew. Chem. 2013, 125, 8992-9047. [2] S. Werner, H. Ebert, A. Achilles, S. Poppe, B.-D. Lechner, A. Blume, K. Saalwächter, C. Tschierske, K. Bacia, Chem. Eur. J. 2015, 21, 8840-8850. [3] S. Poppe, A. Lehmann, A. Scholte, M. Prehm, X. Zeng, G. Ungar, C. Tschierske, Nature Com- munications 2015, 6, 8637.

Acknowledgement: The work was supported by the DFG in the framework of FOR 1145.

Development of Novel Liquid Crystalline J-Aggregates Utilizing Supramolecularly Engineered Perylene Bisimides

Stefanie Herbst, Bartolome Soberats, Pawaret Leowanawat, Matthias Lehmann*, Frank Würthner*

Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg (Germany) E-mail: [email protected], [email protected]

Self-assembly of low-molecular-weight organic molecules like discotic liquid crystals enables the engineering of nanostructured functional materials with potential applications in photonics and optoelectronics.[1] These materials are based on -conjugated scaffolds functionalized by alkyl chains that self-assemble in cofacial manner by - interactions forming columnar liquid crystalline assemblies. This mode of self-organisation leads in general to favourable charge transport properties but unfavourable energy transfer properties due to H-type exciton coupling.[2-4] In the present work, we have designed and synthesised a new type of columnar LC materials based on tetra bay-substituted PBIs bearing four wedge-shape units with flexible chains, while the imide positions contain free NH-groups.[5] The dyes were designed according to supramolecular principles to self-assemble via hydrogen bonding (H-bonding) and - interactions into helically stranded J- aggregates forming LC columnar phases. Here the PBIs are oriented with the transition dipole moment parallel to the columnar axis. We discovered that even small modifications in the molecular design possess great impact on the number of self-assembled strands. Importantly, these compounds can be easily aligned with the molecular axis parallel to the surface, which offers new pathways to obtain photonic materials with highly anisotropic properties.

Figure 1. Schematic illustration of the molecular self-assembly of MEH-PBI and REF-PBI into columnar hexagonal LC phases that exhibit orthogonal orientation of the PBIs.[5]

References [1] E. K. Fleischmann, R. Zentel, Angew. Chem. Int. Ed. 2013, 52, 8810-8827. [2] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2015, 116, 1139–1241. [3] Handbook of Liquid Crystals 2nd Ed. (Eds.: J. W. Goodby, P. J. Collings, T. Kato, C. Tschierske, H. Gleeson, P. Raynes), Wiley- VCH, Weinheim, 2014. [4] F. Würthner, C. Saha-Möller, B. Fimmel, S. Ogi, P. Leowanawat, D. Schmidt, Chem. Rev. 2016, 116, 962−1052. [5] S. Herbst, B. Soberats, P. Leowanawat, M. Lehmann, F. Würthner, Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201612047. Observation of Chiral Structures from Achiral Micellar Lyotropic Liquid Crystals under Capillary Confinement

1 1 2 Clarissa F. Dietrich , Frank Giesselmann *, Per Rudquist

1 Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany. 2 Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg, Sweden. E-mail: [email protected]

The appearance of chirality in a system of achiral components gives rise to fundamental questions about mechanisms of chiral symmetry breaking. Recently the emergence of chiral symmetry broken configurations in achiral chromonic liquid crystals confined in cylindrical capillaries was reported, namely the so-called twisted- escaped radial (TER) and twisted planar polar (TPP) configurations. [1] These new examples of chiral symmetry breaking in liquid crystals were attributed to the twist elastic modulus which is known to be unusually small in the case of chromonic liquid crystals. [1] Strong splay and/or bend deformation can energetically escape into twisting which leads to equilibrium helical structures. In a similar way an unusually small saddle-splay modulus gives stabilized chiral configurations. [2, 3] We now report for the first time the experimental observation of the same chiral TER and TPP configurations in the case of a classical, achiral and non-chromonic lyotropic liquid crystal. The disc- shaped micelles formed by N,N-dimethyl-N-ethyl- hexadecylammoniumbromide in water with 1- decanol as co-surfactant orient homeo- tropically at the capillary glass walls. The nematic director field of the lyotropic liquid crystal adapts extremely slowly to the confinement of capillary geometry and changes its configuration when a magnetic field is applied. Thus, we were able to observe within one system the non-twisted configurations like the escaped radial (ER) and the planar polar (PP) as well as the twisted analogues, the twisted-escaped radial (Fig. 1a) and the twisted planar polar (Fig. 1b). Similarities and differences to the case of chromonic liquid crystals are discussed, in particular we examine the conditions under which chiral symmetry breaking occurs in this standard non-chromonic lyotropic system.

Figure 1: POM observations of a) twisted-escaped radial configuration; b) escaped radial configuration with a change in escape direction (defect) and twisted planar polar configuration observed after being placed in the magnetic field (1 Tesla).

References [1] J. Jeong, L. Kang, Z. Davidson, P. Collings, T. Lubensky, A. Yodh, PNAS 2015, 112, E1837-E1844. [2] Z. Davidson, L. Kang, J. Jeong, T. Still, P. Collings, T. Lubensky, A. Yodh, Phys. Rev. E 2015, 91, 050501. [3] K. Nayani, R. Chang, J. Fu, P. Ellis, A. Fernandes-Nieves, J. Park, M. Srinivasarao, Nat. Commun.2015, 6, 8067.

Confinement of Microparticles at Defects in a Nematic Liquid Crystal

A. Helen Macaskill*, D. Wei, M. Nikkhou, H. F. Gleeson, J. C. Jones

School of Physics and Astronomy, University of Leeds, Woodhouse Lane, LS6 2EN, Leeds, UK E-mail: [email protected]

Dating back to the early years of liquid crystal research, [1] defects have been a well-studied feature of liquid crystal systems. Defects can be stable in certain liquid crystal phases, or under certain anchoring conditions. While there are many reports of particles suspended in a liquid crystal interacting with existing defects, fewer studies quantify the strength of these interactions. [2-4] Understanding the interactions between particles and defects may offer a route to self-assembly and the creation of novel photonic and electro-optic devices. In this recent work, the trajectories of micro-particles were recorded in the vicinity of defects. To quantify confinement strength, the trapping forces were modelled as a potential well. The mean square displacement of each particle trajectory was used to calculate a ‘trap stiffness’ related to the depth of the potential well [5]. Clear evidence of particle confinement near defects was found in a Schlieren cell. The effect of defect type, particle size and surface treatment on confinement will also be discussed.

At long timescales, the mean square displacement of a particle confined at a defect approaches a constant. The mean-square displacement of a non-confined particle is linear with time.

References [1] C. W. Oseen, Trans. Faraday Soc 1933, 29, 883-889. [2] A.V. Rhyzhkova and I. Muševič, Phys. Rev. E 2013, 87, 032501. [3] D. Pires, J. B. Fleury and Y. Galerne, Phys. Rev. Lett, 2007, 98, 247801. [4] R. P. Trivedi, D. Engström and I. I Smalyukh, J. Opt. 2011, 13, 044001. [5] M. Tassieri, R. M. L. Evans, and R. L. Warren et al, New J. Phys, 2014, 14, 115032.

Columnar Liquid Crystals in Cylindrical Confinement

Ruibin Zhang1, Goran Ungar1*, Xiangbing Zeng1, Carsten Tschierske2

1 Dept. of Materials Sci. & Eng., University of Sheffield, Sheffield S1 3JD, U.K. 2 Dept. of Physics, Zhejiang Sci-Tech University, Hangzhou 310018, China 3 Institute of Org. Chem., Martin Luther University, 06120 Halle/Saale, Germany E-mail: [email protected]

Using 2D X-ray diffraction and AFM we studied the configuration, in cylindrical confinement, of hexagonal and square columnar phases with both planar and homeotropic anchoring. A wide range of pore diameters, from 20 nm to 100 µm, were explored by employing anodic alumina membranes and glass capillaries. The compounds used were a small discotic hexakis(hexyloxy)triphenylene (HAT6), a large discotic hexa-peri-hexabenzocoronene (HBC), a minidendron, a hetero-helicene, two T-shaped amphiphiles, and a HAT6-TNF columnar charge-transfer complex. [1,2] The main motivation of studies of this kind is aligning the columns parallel to the pore axis with a view of incorporating the material in optoelectronic devices, including semiconducting, light-harvesting and light-emitting molecular wires. Although intuitively axial alignment is expected, particularly of planar-anchoring columns, it turns out that in most such cases columns form concentric circles in the plane perpendicular to the pore axis. Only the most rigid columns, i.e. those in the HAT6-TNF complex and the helicene, can align axially. When the columns are made to anchor homeotropically, either through surface treatment or choice of mesogen, again the columns align perpendicular to the pore axis, but this time they stretch straight across the pore in what we call the “logpile” configuration. This is the case for nanopores and micropores up to tens of µm in diameter, with intriguing diameter dependence of detailed orientational mode. [3] Surprisingly however, in glass capillaries of tens of µm and beyond, the columns become oriented parallel to the capillary axis. Tentative explanations of this intriguing behaviour is proposed.

Figure. Top: Models of the different configurations of homeotropically anchoring columns in cylindrical pores of increasing diameter. Bottom: SEM images of the corresponding pores, with the diameter indicated.

References [1] R. Zhang, X. B. Zeng, M. Prehm, S. Grimm, M. Geuss, M. Steinhart, C. Tschierske, G. Ungar, ACS Nano 2014, 8, 4000. [2] R. B. Zhang, X. B. Zeng, B.-S. Kim, R. Bushby, K.-S. Shin, P. Baker, V. Percec, G. Ungar, ACS Nano 2015, 9, 1759. [3] R. B. Zhang, G. Ungar, X. B. Zeng, Z. H. Shen, “Diverse Pore-Width Dependent Configurations of Columnar Liquid Crystals in Cylindrical Confinement”, submitted. Designing and Characterising the Soft Elasticity of Acrylate Liquid Crystal Elastomers with Tuneable Physical Properties

a b c a Devesh Mistry *, John Clamp , Philip B. Morgan and Helen F. Gleeson

aSchool of Physics and Astronomy, University of Leeds, Woodhouse Lane, Leeds, UK, bUltraVision CLPL, Commerce Way, Leighton Buzzard, LU7 4RW, bEurolens Research, University of Manchester, Dover Street, Manchester, M13 9PL. E-mail: [email protected]

Liquid crystal elastomers (LCEs) are currently one of the most exciting soft materials with proposed applications ranging from photo-actuated micro-robots to novel chemical sensors.[1,2] The continued discovery of novel applications for LCEs relies on a greater understanding of their fundamental physics along with the development of scalable and novel materials with widely tuneable physical properties. Of particular interest are materials synthesised from blends of monomers with a liquid crystal phase of appropriate width and a tuneable glass transition temperature.[3,4] Here we present such a system of LCEs, but based entirely on acrylate monomers and characterise. By using solely acrylate monomers, the synthesis procedure is fast, scalable and can be performed at room temperature. The Tg of the materials can be tuned between 1.9 and 19.6°C while their TNI can be controlled from room temperature upwards.[5] Using bespoke equipment we investigate the fundamentals of their soft elasticity and dynamics. We further discuss the implications of inhomogeneous distributions of director orientation, stress and strain in LCEs.

Graphs: System of materials show a remarkable tuneability in Tg and large mechanical anisotropy. Photographs: Via polarising microscopy we explore the effects of heat and mechanical stress.

References [1] H. Zeng, P. Wasylczyk, C. Parmeggiani, D. Martella, M. Burresi, D. S. Wiersma, Adv. Mater. 2015, [2] 27, 3383-7 [3] S. Schuhladen, F. Preller, R. Rix, S. Petsch, R. Zentel, H. Zappe, Adv. Mater. 2014, 26, 7247-51. [4] A. Elias, K. Harris, B. Bastiaansen, D.J. Broer, M.J. Brett, J. Mater. Chem. 2006, 16, 2903-2912. [5] G.R. Mitchell, F.J. Davis, W. Guo, R. Cywinski, Polymer, 1991, 32, 1347-1353. [6] D. Mistry, J. Clamp, P.B. Morgan, H.F. Gleeson, in review.

Microfluidic Synthesis of Liquid Crystalline Elastomer Micropumps

a a b Lukas B. Braun , Rudolf Zentel* , Christophe Serra

a Department of Organic Chemistry, Johannes Gutenberg University, Mainz, Germany b Institute of Chemistry and Processes for Energy, Environment and Health, University of Strasbourg, France

E-mail: [email protected]

Photoresponsive liquid crystalline elastomers (LCEs) are promising candidates for an application as artificial muscles in micro devices. When the mesogens in a crosslinked liquid crystalline polymer change their orientation during the light-induced nematic to isotropic phase transition, the polymer backbone relaxes from a stretched into a coiled conformation. For materials with a good mesogen orientation, this results in a macroscopic deformation. [1] A capillary-based microfluidic device enables the fabrication of LCE particles with good control over their size. Due to the high shear between the different phases in flow, a good orientation of the mesogens can be achieved. Applying this method, we produced LCE particles showing a strong, fast and reversible photoresponsive change in length of up to 24%. [2] In this work the microfluidic set-up was modified in order to enable the fabrication of photoresponsive LCE microtubes. For this purpose, a flow-focusing co- axial capillary device was applied, with the inner capillary providing a high viscous aqueous phase as the template for the microtubing’s hole. (Fig. 1) In first experiments, with a thermoresponsive LC-monomer mixture, microtubes could successfully be produced which showed a cross-sectional tapering caused by heating them above the clearing temperature. By moving UV-irradiation parallel to a photoactuating LCE microtube, transportation of a liquid along the inside should be possible, analogous to a peristaltic pump.

Figure 1. a) Microfluidic set-up for the fabrication of LCE microtubes, b) photoresponsive selective cross-sectional tapering of an LCE microtube, c) applied monomer and crosslinker.

References

[1] E. Fleischmann, R. Zentel, Angew. Chem. Int. Ed. 2013, 52, 8810-8827. [2] L.B. Braun, T. Hessberger, R.Zentel, J. Mater. Chem. C 2016, 4, 8670-8678.

Light Induced Mircomanipulation and Defect Formation in Nematic Liquid Crystals via Photovoltaic Fields

Lin Jiao1, Atefeh Habibpourmoghadam1, Dean R. Evans2, Victor Y. Reshetnyak3, Alexander Lorenz1*

1Department of Physical Chemistry, Paderborn University, Warburger Str. 100, 33098 Paderborn, Germany; 2Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA 3Theoretical Physics Department, Taras Shevchenko National University of Kyiv, UA-01601 Kyiv, Ukraine *[email protected]

Exciting experimental results on light induced defect formation and micromanipulation in/of a nematic liquid crystal (LC) film on a highly photo-responsive surface (iron doped LiNbO3) are presented. Samples were investigated in a purpose build setup, where localized responses were induced with a continuous wave laser beam focused to a small spot [1-2] and investigated with polarized probe light in a modified inverted optical polarized microscope. In the presented experiments,[1-2] optically generated electric fields were converted in localized optical responses by the LC. In contrast to previous works [4-6] an imaging approach was used [1-2]. The observed, light induced defects could be successfully explained with electrostatic field simulations. In addition, we could achieve both micromanipulation of responsive particles in a LC (Fig. 1) and micromanipulation of a LC film on a responsive surface (Fig. 2), which is highly promising for lab-on-a- chip technologies and thus for novel applications of LCs.

Fig. 1. Fe doped LiNbO3 particle in a nematic LC, Fig. 2. Nematic LC (open film) on an Fe doped

exposed with a focused laser beam. The sample LiNbO3 surface, exposed with a focused laser beam was observed with crossed polarizers. Image (a) Low laser power, white light illumination. Image sequence (a) through (d) shows particle movement sequence (b) through (d): High laser power, laser (initial position indicated). wavelength filtered form the field of view with an edge pass filter.

References

[1] A. Lorenz, L. Jiao, A. Habibpourmoghadam1, D. R. Evans, 2017 (submitted). [2] Invited: A. Lorenz, A. Habibpourmoghadam, L. Jiao, F. Omairat, D. R. Evans, L. Luccetti, V. Reshetnyak, Poceedings of SPIE, Optics and Photonics, San Diego Meeting 2017, (submitted). [3] J. L. Carns, G. Cook, M. A. Saleh, S. V. Serak, N. V. Tabiryan, S. A. Basun, and D. R. Evans, Molecular Crystals and Liquid Crystals 2006, 453, 83. [4] J. L. Carns, G. Cook, M. A. Saleh, S. V. Serak, N. V. Tabiryan, and D. R. Evans, Optics Letters, 2006, 31, 993. [5] L. Lucchetti, K. Kushnir, A. Zaltron, and F. Simoni, Optics Letters 2016, 41, 333. [6] L. Lucchetti, K. Kushnir, A. Zaltron, and F. Simoni, Journal of the European Optical Society: Rapid Publications 2016, 11.

Acknowledgements: AL acknowledges financial support by German Research Council grants DFG LO 1922/4-1 and GRK 1464. Financial support by the US Air Force Office of Scientific Research (AFOSR) is acknowledged by DRE, support through their European Office of Aerospace Research & Development (EOARD) is acknowledged by AL (grant FA 9550 15-1-0426) and VYR (EOARD/STCU grant P649a).

Industrial Development of Plastic Liquid Crystal Technology

H. Hakemi

It has been over 3 decades that plastic liquid crystals had been developed at industrial scale and into commercial applications. During the same period a substantial number of academic research has been carried out in the scientific literature.

However, the academic and industrial research and development have been mainly in parallel, leaving both entities basically unaware of each other developments. Although the industrial developments have been benefiting from academic works in open literature, the contribution of academics to industrial innovations has been limited.

In this presentation, I would like to make a brief review of evolution history of industrial developments of plastic Polymer Dispersed Liquid Crystal (PDLC) including the technology, products, manufacturing, patent situation, applications and global markets, as well as a review of industrial development of this technology in Europe.

With increasing global demands for plastic liquid crystal products and applications, as well as the emergence of competitive technologies, provides opportunity for new academic-industrial collaborations in research and development in the field liquid crystals.

Electrode Patterning by Nanosphere Lithography for Switchable 2D Blue Phase Gratings

Markus Wahle*,1,2, Katharina Brassat2,3, Justus Ebel1,2, Julius Bürger2,3, Jörg K. N. Lindner2,3, and Heinz- 1,2 Siegfried Kitzerow

1Department of Chemistry, Paderborn University, 33098 Paderborn, Germany 2Center for Optoelectronics and Photonics Paderborn CeOPP, 33098 Paderborn, Germany 3Department of Physics, Paderborn University, 33098 Paderborn, Germany.

E-mail: [email protected]

In this contribution, we propose nanosphere lithography (NSL) as a self- assembly technique for the fabrication of 2D structured electrodes. We use these electrodes to manufacture an electrically switchable blue phase grating. NSL is based on the self-assembly of nano- or micrometer sized spheres into hexagonally closed packed monolayers [Fig. 1(a)]. This allows for cost effective and fast structuring of large areas (~cm2). Shrinking the spheres [Fig. 1(b)] and subsequent metal deposition [Fig. 1(c)] yield structured metal thin films.[1] The prepared electrodes provide a versatile basis for liquid crystal (LC) gratings. Usually, LC gratings rely on electrodes structured by standard techniques, which are limited to periodicities of ≥ 5 µm.[2] This leads to low diffraction angles, which impairs the applicability of these gratings. Most methods to produce smaller structures are cost and time consuming. NSL therefore provides a superior alternative. We combine the NSL-structured electrode with polymer-stabilized blue phases to achieve sub- millisecond switching and polarization independence. The prepared samples show a high diffraction angle [Fig. 1(d)] and a tunable diffraction efficiency [Fig. 1(e)]. The blue phase device can be easily and accurately modelled using the finite element technique [Fig. 1(f)].

1. Shrinki Me ng tal deposit ion 2. Sph by RIE ere remov al

Figure. 1: (a)-(b) SEM images of (a) a self-assembled monolayer of 2 µm spheres, (b) spheres after shrinking by reactive ion etching (RIE). (c) AFM images of the structured electrodes after metal deposition and sphere removal. (d) Diffraction pattern of the LC cell. (e) Diffraction efficiency versus voltage. (f) Simulated diffraction pattern at 76 V (maximum efficiency).

References [1] K. Brassat, F. Assion, U. Hilleringmann, J. K. N. Lindner, Phys. Stat. Sol. A 210, 1485 (2013) [2] L. Gu, X. Chen, W. Jiang, B. Howley, and R. T. Chen, Appl. Phys. Lett. 87, 201106 (2005)

Measurement of Homeotropic Surface Anchoring and Slip in Liquid Crystal Displays through Bistable Latching

Sophie A Jones*, James Bailey, and J Cliff Jones

University of Leeds, Leeds, UK

E-mail: [email protected]

Surface interactions in liquid crystal displays give rise to director alignment and govern aspects of switching behavior. Two surface interaction parameters, the homeotropic anchoring strength and the surface slip length, have been determined in this study by way of latching dynamics at the surface of the zenithal bistable display (ZBD). ZBD uses a deep, homeotropic surface relief grating to support two bistable alignment states corresponding to a low tilt Defect state and a near vertical Continuous state. The two states are selected via flexoelectric switching, and are mediated by the creation / annihilation and movement of ± ½ strength disclinations at the surface. ZBD cells were filled with 4-cyano-4’-pentylbiphenyl and latched using bipolar pulse waveforms. According to previous theoretical descriptions of the device and of flexoelectric switching [3, 4], the latching impulse depends on three factors: the material (flexoelectric constants, elasticity, dielectric anisotropy, and viscosity), the surface (anchoring strength and slip factor), and the external applied field. Since the material used is well-characterised, the measurements allow both the surface parameters to be derived, both anchoring energy and surface slip. Experiments were carried out examining the effects of different grating photopolymers and of temperature. This method was found to accurately reproduce anchoring energies expected from the alignment layers (in the range 5 to 15 ×10-5 J/m2). This study helps to further understanding of the latching mechanisms of ZBD devices and provides a novel method for determining the homeotropic anchoring strength of different homeotropic surface treatments.

References [1] G.P. Bryan-Brown, C.V. Brown and J.C. Jones, US patent 6,249,332 (2000); [2] J.C. Jones, Bistable Nematic LCD, IN J.W. Goodby et al, The Handbook of Liquid Crystals, Springer. (2014) [3] T. J. Spencer, C. Care, R. J. Amos and J.C. Jones, Phys. Rev. E 82, 021702 (2010). [4] A. J. Davidson and N. J. Mottram, Phys. Rev. E 65, 051710 (2002).

Temporal Shape-Evolution of Freely Floating Smectic Bubbles

Patricia Dähmlow*, Torsten Trittel, Ralf Stannarius

Institute of Experimental Physics, Otto-von-Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany

E-mail: [email protected]

Freely floating smectic bubbles are investigated under microgravity conditions. In equilibrium, they form a spherical minimal surface, like soap bubbles. A great advantage of freely floating bubbles is the absence of a meniscus, which acts as a reservoir of smectic material when the surface area of a suspended film changes. In this work, the freely floating bubble must rearrange its internal layer structure without such a reservoir. Experiments were performed during parabolic flights, observing the bubble dynamics with optical highspeed imaging. Bubbles were prepared from collapsing catenoid-shaped films, resulting in an elongated shape after pinch off. The volume and surface area of the bubbles were calculated during the relaxation towards a sphere. As the volume of the bubble is conserved, the volume obtained from image analysis is a measure of the quality of the numerical surface calculation (see Figure). During relaxation, the bubble performs complex oscillations, including invaginations of the film and thus, a temporary increase of the surface area. The relation between the film area relaxation rate and the film thickness of the bubble was analyzed. We propose that the dynamics is largely determined by a specific viscosity term that includes the rearrangement of the smectic layer structure, the formation of new layers and related dislocations in the layer structure.

Temporal evolution of surface area and volume of a freely floating smectic bubble during relaxation towards a sphere.

Microrheology Of Rod-Shaped Particles In Freely Suspended Liquid Crystal Films

Christoph Klopp, Alexey Eremin* and Ralf Stannarius

Institut of Experimental Physics, Otto-von-Guericke University Magdeburg, Universitätsplatz 2, 39106, Magdeburg, Germany

E-mail: [email protected]

Flow phenomena in restricted geometries have been studied in a variety of different physical, chemical and biological systems in the last years. Fluid dynamics in a quasi-2D geometry is particularly interesting for its relevance to the motion of proteins and submicrometre-sized inclusions in biological membranes. Mobility of isometric particles in 2D membranes have been investigated experimentally and theoretically. [1][2] In contrast to the 3D case, the mobility exhibits a distinct non- linear dependence on the particle size and shows various hydrodynamic regimes depending on the membrane size, the viscosities of the membrane material and the surrounding fluid. Although a theoretical model for the mobility of the anisometric particles in 2D was proposed by Levine et al. [3], no experimental studies have been reported yet. In our study, we investigate experimentally the mobility of anisometric particles (glass rods) immersed in thin freely suspended smectic A and smectic C films. Those films, having thicknesses between two molecular layers up to micrometres, provide us with an excellent model system of a 2D isotropic liquid and a 2D nematic. Observing Brownian motion of glass rods, we determine the mobility and the drag force as a function of their size and the system parameters. We compare our results with the existing theories of Saffman and Delbrück [2] and Levine [3], and demonstrate the effect of particle anisometry. Measurable effects of shape anisotropy appear when the length of the particles is comparable to or larger than the hydrodynamic size of the system defined by the Saffman length. Our data confirm the predictions of Levine’s theory. [3]

References

[1] A. Eremin, S. Baumgarten, K. Harth, R. Stannarius, Physical Review Letters 2011, 107, 268301 [2] Z. H. Nguyen, M. Atkinson, C.S. Park, J. Maclennan, M. Glaser, N. Clark, Physical Review Letters 2010, 105, 268304 [3] J. Levine, T. B. Liverpool, F. C. MacKintosh, Physical Review Letters 2004, 93, 038102

Poiseuille Flow of Exotic Emulsions Containing Nematic Liquid Crystals

Fraser Mackay*, Davide Marenduzzo

School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, UK

*E-mail: [email protected]

Although many equilibrium properties exhibited by liquid-crystal emulsions are now well understood [1], there is still much to be learned about how droplets behave when subject to external influences, for example flow fields. Recently, studies have been conducted on the behaviour of a single-droplet, inverted nematic emulsions in the presence of shear flow, demonstrating the dynamical evolution of both the isotropic droplet and the nematic director field [2].

Going beyond the single-droplet level, we present here the first results on the flow of an inverted 2D nematic emulsion consisting of several isotropic droplets in a nematic solvent. Using the lattice Boltzmann method [3], we have studied the effect of subjecting the system to Poiseuille flow and have observed a phase change in the viscosity. This results in the presence of two domains depending on the pressure gradient applied to the emulsion wherein below a critical point the flow is arrested and above which the system is observed to flow freely through the channel. We have seen that the liquid crystal bulk parameters, the thermal energy scale and the liquid crystal elastic constant govern the position of this critical pressure gradient most significantly. These results provide an interesting insight into the behaviour of this type of exotic emulsion when subjected to a Poiseuille flow.

References:

[1] Y. Li, J. Jun-Yan Suen, E. Prince, et al, Nat. Comm., 2016, 7, 12520; D. Sec, T. Porenta, M. Ravnik, S. Zumer, Soft Matter, 2012, 8, 11982. [2] A. Tiribocchi, M. Da Re, D. Marenduzzo and E. Orlandini, Soft Matter, 2016, 12, 8195-8213. [3] N.Sulaiman, D. Marenduzzo and J. M. Yeomans, Phys. Rev., 2006, 74, 04170

Elasticity of Smectic Liquid Crystals with In-Plane Orientational Order, and Dispiration Asymmetry

Buddhapriya Chakrabarti*1, Yashodhan Hatwalne2, Jayakumar Alageshan2

1Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield, S3 7RH, UK. 2Raman Research Institute, C. V. Raman Avenue, Bangalore 560 080, INDIA.

E-mail: [email protected]

The Nelson-Peliti formulation [1] of the elasticity theory of isolated uid membranes with orientational order emphasizes the interplay between geometry, topology, and thermal fluctuations. Fluid layers of lamellar liquid crystals such as smectic-C, hexatic smectics, and smectic-C* are endowed with in-plane orientational order. We extend the Nelson-Peliti formulation so as to bring these smectics within its ambit. Using the elasticity theory of smectics-C* we show that positive, and negative dispirations (topological defects in Smectic-C* liquid crystals) with strengths of equal magnitude have disparate energies, a result that is amenable to experimental tests.[2]

Figure 1. The planar surface Li labels the ith smectic layer in the reference lattice of SmA, with inter-layer spacing d. Making a vertical cut C (shaded rectangle) through the layers, identifying the left lip of the cut on Li-1 to the right lip of the cut on Li, and letting the system relax leads to the right-handed, half-helicoidal surface shown. This is the Volterra construction of a screw dislocation. The z-axis is the singular dislocation line, and b = d zis the Burgers vector.

References [1] D. R. Nelson and L. Peliti, J. Physique 1987, 48, 1085-1092. [2] J. Alageshan, B. Chakrabarti, and Y. Hatwalne, Phys Rev E 2017, 95, 022701-022708. Light Emission in Cholesteric Films: Temperature and Angular Dependence

Jürgen Schmidtke*

Faculty of Science, University of Paderborn, Warburger Str. 100, 33098 Paderborn, Germany

E-mail: [email protected]

Due to the presence of a selective reflection band, cholesteric liquid crystals strongly modify the emission of fluorescent guest molecules. Emission along the helical axis – for wavelengths outside of absorption bands – has been studied experimentally as well as theoretically a long time ago and is quantitatively understood.[1] However, there still is a lack in quantitative understanding of the effects of absorption on the emission, and also of the emission properties at oblique angles with respect to the cholesteric helix. We present a systematic study of the temperature and angular dependent emission properties of a cholesteric film doped with a fluorescent dye. Temperature variation results in a shift of the selective reflection band. Weak overlap with the dye’s absorption band already completely eradicates the short- wavelength band edge resonance (at low temperature, cf. Fig. 1a), which only shows up at higher temperatures, where the reflection band is sufficiently red-shifted (Fig. 1b). Angular dependent measurements (obtained at several temperatures) show a continuous blue shift of the resonances with increasing angle with respect to the helical axis, accompanied with an overall degradation of the resonance peaks (cf. Fig. 1c). This results in a strong angular dependence of emission intensity as well as emission polarisation.

Fig.1. Ratio of right- and left-handed circularly polarised emission contributions along the helical axis, obtained at 34 °C (a) and 41 °C (b); angular-dependent emission: right-handed circularly polarised emission contribution, obtained at T = 37 °C in an angular interval = 0°…20° (c).

References

[1] J. Schmidtke and W. Stille, Eur. Phys. J. B 2003, 31, 179-192

Methyl Red Doped Liquid Crystals and their Combination with Metamaterials

Bernhard Atorf* and Heinz-Siegfried Kitzerow

Department of Chemistry and Center of Optoelectronics and Photonics Paderborn, Paderborn University, Warburger Straße 100, 33098 Paderborn, Germany

E-mail: [email protected]

Optical metamaterials composed of metal nanostructures can exhibit very unusual optical properties[1] owing to the interaction of electromagnetic waves with plasmonic resonances. If the size of the optically active structures composing the metamaterial is in the range of a few 100 nm, these resonances appear in the infrared (IR) spectral range and are typically investigated in IR microscope connected to a spectrometer. Combination with a liquid crystal yields tuneable properties: The wavenumbers of the resonant modes are shifted by an applied electrical field due to the director reorientation[2]. In principle, the optical resonances could also be shifted through the nonlinear response of a dye-doped liquid crystal. For example, the refractive index of methyl red- doped liquid crystals is known to be extremely sensitive to optical radiation owing to the colossal optical nonlinear effect[3]. This effect is based on a surface induced reorientation of the liquid crystalline director[4]. To study the huge nonlinear response and to measure the influence on the optical resonances of the metamaterial we couple a green laser beam into the path of an IR microscope-spectrometer setup (Fig. 1). If a homeotropic cell (filled with a methyl red-doped liquid crystal) is illuminated with a green laser beam, which is linearly polarized at an azimuthal angle of 45° with respect to the polarization of the infrared radiation, the liquid crystal tends to align along the polarization of the laser beam (Fig. 2). We discuss different strategies to use the huge nonlinear response in combination with metamaterials.

Fig. 1: Adjustment in the Fig. 2: Effect of a green cw laser on a methyl red-doped liquid crystal IR- spectrometer for the in a homeotropic cell: Deviation (Δφ) of the azimuthal angle of the coupling of the green director from the plane of polarization of the laser light versus laser. illumination time.

References

[1] W. Cai, V. Shalaev “Optical Metamaterials” 2010, Springer [2] B. Atorf, H. Mühlenbernd, M. Muldarisnur, T. Zentgraf, H. Kitzerow, Opt. Lett. 2014, 39, 1129-1132 [3] L. Lucchetti, M. Di Fabrizio, O. Franescangeli, F. Simoni, Opt. Commun. 2004, 233, 417-424 [4] L. Lucchetti, F. Simoni, Phys. Rev. E 2014, 89, 032507

Higher Ordered Smectic Liquid Crystals as Semiconductors in Organic Field-Effect Transistors

a a b Iris Wurzbach , Frank Giesselmann *, Christian Rothe , Sabine Ludwigs

a Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany b Institute of Polymer Chemistry, University of Stuttgart, 70569 Stuttgart, Germany E-mail: [email protected]

Since the 1990s discotic liquid crystals with columnar phases are well known as one dimensional organic semiconductors. However, electronic charge transport in smectic phases of rod-like mesogens has been investigated far less. Due to the layered structure, charge carriers can in principle easily diffuse in two dimensions along the smectic layers and the charge transport is thus expected to be less sensitive to structural defects than the 1D transport in columnar phases. Mainly higher ordered smectic phases are considered as potential 2D semiconducting materials since the molecular order and the packing density inside the smectic layers is high. So far charge transport in smectics has only been studied in detail for a few examples of 2-phenylnaphthalene-, terthiophene-, 2-phenylbenzothiazol- and benzo- [b]benzo[4,5]-thieno[2,3-d]thiophene-derivatives.[1,2] We now report a first systematic study of the 2D charge transport properties of 5,5''-dioctyl-2,2':5',2''- terthiophene with tilted liquid crystalline SmC, SmF and G phases [3] using a field-effect transistor (FET) setup. The smectic layers as well as the direction of the director tilt were aligned on the substrate via mechanical shearing. The measured FET mobilities decreased with increasing temperature from the crystalline phase down to the fluid SmC phase (Fig. 1a). The mobilities in the smectic phases are in the range of 10–4 – 10–5 cm2 V–1 s–1. For the first time we measured the anisotropy of the intralayer mobility parallel and normal to the tilt direction (fig. 1b). The anisotropy turned out to be surprisingly high (μ⊥ / μǀǀ ≈ 10) in the G phase. Based on these results the charge transport properties in smectic liquid crystals are compared to the properties of their discotic counterparts.

Fgure 1: a) Measured FET mobilities (μFET) depending on the temperature and b) transistor substrates with aligned liquid crystalline films prepared by mechanical shearing parallel and perpendicular to the applied electric field.

References

[1] M. Funahashi, Polym. J. 2009, 41, 6, 459-469. [2] H. Iino, J.-I. Hanna, Polym. J. 2017, 49, 1, 23-30. [2] N. Boucher, J. Leroy, S. Sergeyev, E. Pouzet, et al., Synthetic Metals 2009, 159, 13, 1319-1324. Mechanism of Enhancement of Electrooptic Switching Time of Ferroelectric/Gold Nanoparticles Nanodispersions

Fedor Podgornov1,2) *, Victor Boronin2 , Wolfgang Haase1,2

1)Eduard Zintl Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Alarich Weissstr. D-64287, Darmstadt, Germany 2)Laboratory of Molecular Electronics, South Ural State University, Chelyabinsk, Lenin ave. 76, 454080, Chelyabinsk, Russia *E-mail: [email protected]

As follows from numerous reports, the dispersing of practically any type of nanoparticles in liquid crystals (LCs) leads the improvement (decrease) its electroooptic switching time. One of the most frequent explanation of this effect is the decrease of the rotational viscosity of LCs. In this report we will demonstrate that the most probably the main reason of the response time enhancement is the increasing the voltage dropping over LC layer due to the trapping of impurity ions with nanoparticles. Here we present of our results on experimental investigation and numerical simulation of the dependence of rotational viscosity of FLC doped with both gold nanospheres (GNS) and gold nanorods (GNRs). Electrooptical measurements showed the decreasing of the response time (Fig.1a) and spontaneous polarization (Fig.1b) of FLC/GNRs and FLC/GNSs nanodispersions in comparison with those of a pristine FLC. The enhancement of the switching time (Fig.1a) of the FLC doped with both gold nanospheres (GNS) and gold nanorods GNRs by the ions trapping (by nanoparticles) leading to the modification of the parameters (mainly, Rlc-FLC layer resistance) of the equivalent electric circuit (EEC) of FLC cell (Fig.1c) [2]. 0

Figure1: Switching time (a) and spontaneous polarization (b) of pristine FLC, FLC/GNSs FLC/GNRs dispersions (concentration- 0.1 % wt.); simplified equivalent electric circuit of a FLC cell (c); Interaction of a gold nanorod with a chiral molecule (d).

Using the parameters of EEC retrieved from the impedance spectra, the electric field (E) in a FLC layer (right side of EEC) was calculated. Finally, it was demonstrated that the rotational viscosity (γφ=τPsE) remains independent on the presence of nanoparticles. BaTiO3 Nanoparticles in Nematic and Ferroelectric Liquid Crystal Phases

S. Al-Zangana1, M. Turner2, I. Dierking1*

1 School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK 2 Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK E-mail: [email protected]

Barium titanate (BaTiO3) exhibits a particle size dependent spontaneous polarization; below diameters of approximately 100nm the material is paraelectric, only becoming ferroelectric for larger sizes. We have doped nematic and ferroelectric liquid crystal (FLC) mixtures with barium titanate nanoparticles of different size to compare the effect of para- and ferroelectric nanoparticles on the properties of these liquid crystals,[1] namely the localization and aggregation of nanoparticles, phase transition temperatures, dielectric behaviour and electro-optic parameters, such as threshold voltage and response time in the case of the doped nematic and tilt angle, polarization, viscosity and response time in the case of the FLC. It was found that phase transition temperatures N-Iso. and SmA*-SmC* were hardly affected at all. At low concentrations the nanoparticle aggregates collect in point defects or at domain walls, while at larger concentrations fractal clusters are observed which exhibit a fractal dimension of D=1.9, indicating a percolation network. In the case of the nematic phase, the addition of small sized paraelectric nanoparticles did not alter the dielectric properties, as expected. Adding larger sized, ferroelectric nanoparticles, showed a marked increase of while stayed practically constant as a function of nanoparticle concentration, thus increasing the dielectric anisotropy . This can be attributed to a partial alignment of the BaTiO3 polarization in the nematic phase. The electro-optic parameters were independent of the properties of the nanoparticles, only depending on concentration, with the threshold voltage increasing, the on-time being constant and the off-time decreasing with increasing BaTiO3 concentration. For the ferroelectric liquid crystal practically no significant effect of the dispersed nanoparticles could be detected, with the tilt angle, spontaneous polarization, response time and rotational viscosity, determined by three different methods, exhibiting the same temperature dependence of values as the neat liquid crystal mixture. Also the dielectric Goldstone mode relaxation was not significantly affected. These observations suggest that the polarization of the BaTiO3 particles is randomly oriented within the FLC and does not change its direction.

References [1] S. Al-Zangana, M. Turner, I. Dierking, J. Appl. Phys., submitted Dielectric Electro-Optical Properties and Absorbance Spectra of Ferroelectric Liquid Crystal Dispersed with Silica Oxide Nanospheres

Pankaj Kumar Tripathi and Shri Singh*

Department of Physics, Banaras Hindu University, Varanasi-221005, India E-mail: [email protected]

In present work, we report tailor-made properties by dispersing nano sized silica oxide (nSiO2) in the ferroelectric liquid crystal (FLC) and have been discussed in the view of dielectric parameter, electro-optical parameter and UV-VIS absorbance spectra. The experimental results indicate that incorporating a minute amount of the nSiO2 (1μl and 10 μl wt%) in the FLC host leads to the suppression of the ionic effect caused by impurity ions. An improvement in spontaneous polarization, response time in nSiO2 dispersed FLC samples compared to FLC is observed and explained on the basis of dipole moment and anchoring phenomena. Practically, the dispersed FLC samples with nSiO2 content show improved dielectric permittivity. In order to gain insight into the dielectric and electro- optical effect, the electro-optical parameters were assessed systematically. Taken together, our results uncover nanospheres as a promising candidate for designing high response display devices. The results have been interpreted both experimentally and theoretically.

Figure 2. Polarizing optical micrographs of pure FLC material, KCFLC10S and nSiO2/FLC composites filled in sample cell with a thickness of 5μm at room temperature showing bright and dark states. The bright and dark states of the sample are observed under a polarizing optical microscope, upon rotating the sample cell without any external bias field (ultimately the rotation of the director). Scale bar: 100μm. Arrow shows the rubbing direction and crossed arrows represent a crossed polarizer (P) and analyser (A). (i) KCFLC10S pure (ii) KCFLC10S+1μl SiO2 (ii) KCFLC10S+10μl SiO2

References [1] P.K. Tripathi, A. K. Misra, S. Manohar, S.K. Gupta, R. Manohar, J. Mole. Stru., 2013, 1035, 371–377. [2] F. Haraguchi, K. Inoue, N. Toshima, S. Kobayashi, and K. Takatoh, Jap. J. Appl. Phys. 2007, 46, L796–L797. [3] T. Joshi, A. Kumar, J. Prakash, and A.M. Biradar, Appl. Phys. Lett. 2010, 96, 253109.

Lyotropic Liquid Crystals from Graphene Oxide

S. Al-Zangana1, M. Iliut2, M. Turner3, A. Vijayaraghavan2, I. Dierking1*

1 School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK 2 Material Science, University of Manchester, Oxford Road, Manchester M13 9PL, UK 3 Department of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK E-mail: [email protected]

Graphene-oxide, like a number of other shape-anisotropic nanoparticles, for example tobacco mosaic viruses, nanotubes, or mineral nano-crystallites, can form a lyotropic nematic phase in water.[1] In this investigation we extend the investigation to two-dimensional colloidal particles of graphene-oxide (GO) varying flake size and concentration in several isotropic solvents with different polarity. The phase behaviour is characterized, and discussed also in relation to a sample thickness dependence. We also demonstrate the effects of boundary conditions and spatial confinement on the formation of the lyotropic nematic phase of graphene oxide, which poses restrictions on the exploitation of these materials in proposed applications.[2]

We will further demonstrate the existence of a newly developing dielectric relaxation related to the graphene oxide within some solvents. This will be interpreted in terms of non-collective fluctuations of the graphene oxide sheets, together with trapped water molecules on the GO surface. The temperature and cell gap dependence of this relaxation will be reported.[3]

An interesting behaviour can be observed when using a thermotropic liquid crystal as the solvent for graphene oxide. At the transition from the thermotropic nematic phase of the solvent to its isotropic liquid, the latter starts to act as an isotropic solvent for the formation of a lyotropic nematic phase. This is demonstrated by polarizing optical microscopy and dielectric spectroscopy.[4]

References [1] Ji Eun Kim, Tae Hee Han, Sun Hwa Lee, Ju Young Kim, Chi Won Ahn, Je Moon Yun, Sang Ouk Kim, Angew. Chem. Int. Ed., 50, (2011), 3043 [2] S. Al-Zangana, M. Iliut, M. Turner, A. Vijayaraghavan, I. Dierking, Nanoscale, submitted [3] S. Al-Zangana, M. Iliut, G. Boran, M. Turner, A. Vijayaraghavan, I. Dierking, Scientific Reports, 6, (2016), 31885 [4] S. Al-Zangana, M. Iliut, M. Turner, A. Vijayaraghavan, I. Dierking, Adv. Opt. Mater., (2016), DOI: 10.1002/adom.201600351

Polarization Effects of Carbon Nanotube Sheets used as Aligning and Conductive Layers for Liquid Crystals

1 1 2 2 1 MD Asiqur Rahman *, Ji Hyun Park , Kieu Truong , Dongseok Suh , Giusy Scalia

1Physics and Material Science Unit, University of Luxembourg, Luxembourg 2Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea E-mail: [email protected]

Carbon nanotubes (CNTs) [1] have unique electronic, optical, mechanical, and thermal properties, which make them very important in nanoscience and nanotechnology. The nanometer- scale thickness, transparency, flexibility, and high work function of CNTs sheets are promising for realizing layers for liquid crystals (LCs) on both flexible plastic and rigid glass substrates. If the CNTs form uniformly oriented sheets ( see Figure 1) they can be used as multifunctional layers that can replace ITO thanks to the conductive and optical properties but also act as alignment layers [2] [3] However, successful application and integration of carbon nanotubes with LC into new devices requires fundamental understanding of their properties and of the possible effects on the LC. LC films are transparent media while CNTs absorb light in an anisotropic manner and the transparency of their sheets decreases as the number of superimposed CNT layers increases. In this study, the polarization of light was investigated finding an effect even when light propagates through just one CNT sheet. The origin of the influence on the light polarization is likely due to the anisotropic absorption of the CNT sheets. The results of this study help gaining a better understanding of the optical properties of aligned CNT sheets deposited on substrates for applications in various optical systems.

Figure 1: CNT sheets from a CNT forest (Nature Communications 7, Article number: 10600)

References

[1] S. Iijima, “Helical microtubules of graphitic carbon,” Nature 1991, 354, 56–58. [2] Schindler, A., Spiessberger, S., Hergert, S., Fruehauf, N., Novak, J. P. and Yaniv, Z. (2008), Suspension-deposited carbon- nanotube networks for flexible active-matrix displays. Journal of the Society for Information Display, 16: 651–658. [3] J. M. Russell et al. Thin Solid Films, 2006, 509, 53-57; W. Fu et al. Carbon, 2010, 48, 1876-1879 Sheets of Oriented Carbon Nanotubes as Multifunctional Substrates for Liquid Crystals

1 2 1 1 2 Giusy Scalia*, Ji Hyun Park , Thuy Kieu Truong , Rahman MD Asiqur , Martin Urbanski , Dongseok Suh

1Physics and Material Science Unit, University of Luxembourg, Luxembourg 2Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea E-mail: [email protected] Carbon nanotubes (CNTs) either deposited on substrates by dip-coating or in continuous wires forming sheets have shown to be able to induce alignment in nematic LC [1]. In the present study free standing CNT sheets which are drawn mechanically from vertically-grown multiwalled CNT forests were deposited on glass substrates (see Figure 1 a) as multifunctional layers for liquid crystal. In fact they successfully align liquid crystal molecules unidirectionally, along the pulling direction of the CNT sheets, as visible in Figure 1b, but also electric fields can be applied that reorient LC. Therefore static and dynamic alignment can be induced on the LC just by using a single CNT sheet. These CNT layers have shown the ability to anchor LC molecules which in fact recover their alignment after phase transition in standard cells, prepared with one or both substrates coated with aligned CNTs and filled with 5CB or E7 nematic LCs, However, we have encountered various challenges such as the poor adhesion of the CNT strands on the surface of glass or silicon substrates and the presence of mobile tubes that cause short-circuits in the cell. Strategies for improving the CNT adhesion on ITO coated glass substrates were explored obtaining good results by the aid of solvents. Inorganic layers were deposited on top of the sheets efficiently acting as insulating layers. We were then able to electrically switch the liquid crystal finding very good electro-optic performance. Finally, we have also investigated the effect of aligned CNTs on the light polarization finding a measurable influence on its orientation. Our results show that aligned CNT sheets are efficient aligning, transparent and conductive electrodes but have also interesting optical characteristics. These properties make them very appealing materials for LC displays and other optical devices. .

Figure 1: a. MWCNT sheets pulled from a forest (on the left), b. polarizing microscopy image of E7 that aligns along the long axis of MWCNT sheets at room temperature

References [1] J. M. Russell et al. Thin Solid Films, 2006, 509, 53-57; W. Fu et al. Carbon, 2010, 48, 1876-1879. Orientational Ordering of Anisotropic Nanoparticles in Diblock Copolymers

Mikhail A. Osipov1,2* , Maxim V/ Gorkunov3 and Yaroslav V. Kudryavtsev2

1Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, Richmond Street, Glasgow, Scotland, UK 2Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninsky Pr. 29, 119991 Moscow, Russia 3 Institute of Crystallography of Federal Scientific Research Centre “Crystallography and Photonics” of Russian Academy of Sciences 119333 Moscow, Russia E-mail: [email protected]

Nematic liquid crystals (LCs) and block copolymers doped with nanoparticles possess a number of enhanced properties, and a small concentration of nanoparticles can shift the transition temperatures between different phases, The use of anisotropic nanoparticles opens a possibility to align block copolymers by external fields which may help to solve various application problems.

Recently a molecular theory of nematic LCs doped with anisotropic nanoparticles has been developed [2-5] and the effect of nanoparticles on the N-I phase transition, the nematic ordering of nanoparticles and the formation of chains of polar nanoparticle have been considered.

We present the results of a molecular theory of the induced orientational order of anisotropic nanoparticles in the lamellae and in the hexagonal phase of a diblock copolymer in the case of both strong and weak segregation taking into account isotropic and anisotropic interaction between nanoparticles and the polymer chains. Numerical concentration and orientational order parameter profiles are presented for different values of the model parameters including the block size, interaction radius and the strength of the anisotropic interaction [1]. The effect of nanoparticles on the stability of these phases is also considered.

We also present the results of the computer simulations of the lamellae and hexagonal copolymer nanocomposites doped with nanoparticles of different length, and the simulated concentration and order parameter profiles are compared with theoretical results. It has also been confirmed by simulations that the nanoparticles may induce a transition from the lamellae to the hexagonal phase.

Acknowledgments M.A.O and Ya.V.K are grateful to Russian Science Foundation, Grant 16-13-10280. for financial support.

References [1] M.A. Osipov and M.V. Gorkunov, Eur.Phys.J., 39, 126 (2016) [2] M.V. Gorkunov and M.A. Osipov, Soft Matter, 7, 4348 (2011) [3] M.V. Gorkunov, G.A. Shandryuk, A.M. Shatalova, I.Yu. Kutergina, A.S. Merekalov, Ya.V. Kudryavtsev, R.V. Talroze, and M.A. Osipov, Soft Matter 9, 3578 (2013) [4] M.A. Osipov and M.V. Gorkunov, ChemPhys.Chem. 15, 1496 (2014) [5] M.A. Osipov and M.V. Gorkunov, Phys. Rev. E , 92, 032501 (2015)

The Nematic Twist-Bend Phase In Liquid Crystalline Dimer Mixtures

Nina Trbojevic*, Mamatha Nagaraj, Daniel J Read

School of Physics and Astronomy, E C Stoner Building, University of Leeds, Leeds, LS2 9JT

E-mail: [email protected]

The nematic twist bend (NTB) phase is a recently discovered nematic liquid crystal phase exhibiting important physical properties. Amongst these significant phenomena is its spontaneous [1,2] helical ordering of nanoscale pitch (< 10 nm) . The NTB phase was first identified for the dimer CBC7CB (1,7-bis(4-cyanobiphenyl-4′-yl)heptane)[3], a calamitic liquid crystal consisting of two rigid cyanobiphenyl cores linked via a flexible methylene spacer. It possesses a higher-temperature nematic phase that, upon cooling, transitions to the NTB phase. It is also similar in structure to the well-studied nematic liquid crystal 5CB (4-cyano-4'-pentylbiphenyl). In this study, the influence of adding a series of 5CB wt% concentrations to pure CBC7CB was investigated. It was observed that by increasing the 5CB wt% concentration, the clearing temperatures of the mixtures decreased linearly. This also occurred for the N-NTB transition temperatures up to a 25 wt% concentration of 5CB. Real and imaginary parts of the dielectric permittivities were measured as a function of frequency over the range 102 – 106 Hz. High frequency relaxation peaks were observed, which upon cooling from the isotropic state were shifted towards lower frequencies.

References

[1] D. Chen, J. H. Porada, J. B. Hooper, A. Klittnick, Y. Shen, M. R. Tuchband, E. Korblova, D. Bedrov, D. M. Walba, M. A. Glaser, et al., Proc. Natl. Acad. Sci. 2013, 110, 15931–15936. [2] A. Hoffmann, A. G. Vanakaras, A. Kohlmeier, G. H. Mehl, D. J. Photinos, Soft Matter 2015, 11, 850– 855. [3] M. Cestari, S. Diez-Berart, D. A. Dunmur, A. Ferrarini, M. R. de la Fuente, D. J. B. Jackson, D. O. Lopez, G. R. Luckhurst, M. A. Perez-Jubindo, R. M. Richardson, et al., Phys. Rev. E 2011, 84, 31704.

Anomalously Low Elastic Constants Measured For A Bent-Core Nematic Liquid Crystal

Shajeth Srigengan1*, Mamatha Nagaraj1, Richard Mandle2, Stephen Cowling2, John Goodby2 and 1 Helen F. Gleeson

1School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK 2Department of Chemistry, University of York, Heslington, York YO10 5DD, UK

Email: [email protected]

The elastic constants K11, K22, K33 (splay, twist and bend respectively) are typically used to describe the elastic behaviour of nematic liquid crystals.[1] Indeed, the elastic properties determine a liquid crystal’s behaviour under external stimuli (eg. an electric field) and can give insight into properties such as the threshold voltage and response time, which are necessary for optimizing any display application. This paper reports the elastic behaviour of a bent-core nematic liquid crystal (compound 1 in Figure 1). The results indicate that this system exhibits very low elastic constant values. Another related bent-core nematic liquid crystal has already been shown to exhibit anomalously low elastic constant values.[2-4] We compare the behaviour of compound 1 with other oxadiazole materials that exhibit nematic phases to allow a deeper understanding of the behaviour of these systems.

Figure 1: Molecular formulas of compound 1, where Iso stands for isotropic, N stands for nematic, SmX stands for smectic of undefined type and Cr stands forCompound crystalline. Temperatures1 are given in degrees Celsius.

Iso 115 N 88 SmX 64 Cr

References [1] F.C. Frank, Discuss. Faraday Soc., 1958, 25, 19 S.Kaur et al., Phys. Rev. E, 2012, 86, 041703 [2] S. Kaur et al., J. Mat. Chem. C, 2013, 1, 6667 [3] H.F. Gleeson et al., ChemPhysChem, 2014, 15, 1251

The author would like to acknowledge the EPSRC and MERCK for funding

Flow of Active Nematics in Confined Geometries

Josh Walton*, Nigel Mottram, Geoff McKay

Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond Street, Glasgow G1 1XH, UK E-mail: [email protected]

We consider the behaviour of an active nematic liquid crystal confined to a shallow polygonal well. Our theoretical analysis is based on extended Ericksen-Leslie equations [1,2] such that the stress tensor comprises of the usual viscous stress and an additional active stress term which accounts for the activity of the nematic material. In the weak Ericksen number limit, the director structure is dominated by surface anchoring and bulk elasticity effects, rather than flow effects. In this situation, and for the particular case of a rectangular well, we find analytic forms of the director structure and energy of a variety of stable states. For relatively strong anchoring, defect-like structures of various strengths are present at the corners of the well.

We then consider the flow behaviour of the active nematic close to the corners of the polygonal well, looking at the general case of a defect of strength k and a corner of angle (see Figure below). For this situation, the Navier-Stokes equations reduce to a forced biharmonic equation. Assuming planar anchoring of the director at the boundaries and no-slip conditions for the flow velocity, we find analytical solutions for the flow velocity by employing a known solution for the director angle [3]. For differing director structures within the corner region we find a variety of flow structures. Potential flow patterns close to corners, walls and flat plates are then investigated.

Figure: Director structure (indicated by the white arrows) and the streamlines (black lines) around a defect of strength k=5 in a corner of angle =/4.

References [1] J.L. Ericksen, Conservation Laws for Liquid Crystals, Trans. Soc. Rheol. 1961, 5, 23-34. [2] F.M. Leslie, Some constitutive equations for liquid crystals, Arch. Rat. Mech. Anal. 1968, 28, 265-283. [3] L. Giomo, M.J. Bowick, P. Mishra, R. Sknepneck, M.C. Marchetti, Defect dynamics in active nematics, Phil. Trans. R. Soc. A 2014, 372, 20130365. A Nematic to Nematic (N-Nx) Transition in a Polar Calamitic Liquid Crystal

Richard J. Mandle 1, Stephen J. Cowling 1 and John W. Goodby 1

1 The University of York, York, UK E-mail: [email protected]

Materials exhibiting more than one nematic mesophase are highly topical due to the discovery of, and continued interest in, the twist-bend nematic phase. [1,2] We have recently synthesized and characterized a novel, highly polar rod-like material that exhibits a clear first order phase transition from a ‘classical’ nematic phase into a lower temperature nematic phase.[3] Both mesophases are assigned as nematic based on POM and SAXS studies. Both the upper (N) and lower (Nx) temperature nematic phases exhibit a response to applied electric fields that is consistent with their identification as nematic. The relatively low dielectric anisotropy is taken to be indicative of extensive antiparallel pairing, the degree of which is significantly greater in the Nx phase.

A) plot of scattered X-ray intensity as a function of 2θ in the N, Nx and Cr phases, B) wide angle scattering in the N and Nx phases, 2D SAXS patterns of the N phase (C, 165 °C), Nx phase (D, 70 °C) and Cr phase (E, 42 °C)

References [1] D. Chen, et al. PNAS, 2013, 110, 15931 – 15936. [2] V. Borshch, et al. Nature Communications, 2013, 4, 2635. [3] R. J. Mandle et al., Manuscript Submitted, 2017.

Does the Magic Angle Promote the Formation of Nematic Liquid Crystals?

Stefan Maisch and Matthias Lehmann*

Institut of Organic Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany E-mail: [email protected]

The tetrahedral angle (“magic angle”) has been claimed to be most promising for V-shaped nematogens to realise the biaxial nematic liquid crystal phase.[1] The benzo[1,2-b:4,3-b’]dithiophene core is a bent unit accomplishing the 109.4 ° angle and additionally possess a small dipole along its bisector, which has been proposed to further stabilise a biaxial phase.[2] Recently, a nematogen with the benzodithiophene core and four lateral chains has been shown to reveal a monotropic biaxial nematic phase.[3] We aim the synthesis of bent core derivatives consisting of arms with alicyclic building blocks and terminal pentyl chains, which conventionally promotes the formation of nematic phases at low temperature. Here we present the mesomorphic properties of a series of new hockey stick, dimer and V- shaped nematogens. Exclusively the hockey-stick mesogens assembled in uniaxial nematic phases over a broad temperature range – all other materials crystallised. Single crystal structure analysis of 1 and 5 gives insight in the molecular packing and allows to explain the absence of mesophases for the V- shaped derivatives.

References [1] G.R. Luckhurst. Thin solid films 2001, 40, 393. [2] M. A. Bates, Chem. Phys. Lett. 2007, 437, 189. [3] J. Seltmann, K. Müller, S. Klein, M. Lehmann. Chem. Commun. 2011, 47, 6680.

Influence Of Molecular Bend Angle On The Twist-Bend Nematic Mesophase.

Richard J. Mandle 1, Craig T. Archbold 1, Jessica L. Andrews 1, Julia P. Sarju 1 and John W. Goodby 1

1 The University of York, York, UK E-mail: [email protected]

Over recent years dimeric liquid crystals have been found to exhibit a variety of fascinating mesomorphic properties. Some bimesogens having a spacer of odd parity exhibit a transition from a nematic phase to the twist-bend nematic phase (NTB). [1-4]

Plot of the NTB-N and N-Iso transition temperatures versus the weigted average molecular bend angle for some cyanobiphenyl dimers with varying linking group and spacer composition.

By varying the linking units we can affect a change in the intermesogen angle; previously we assumed this to be equal to that of the all trans form (supported by NMR) [5] however in the present work we have studied the conformational landscape of each material computationally allowing us to use a bend angle that is the weighted average of all conformers which is perhaps an improvement over our earlier study. [5] The present results are a further demonstration that the stability of the NTB phase exhibits a strong dependency on not only the bend angle of the molecule but also the flexibility afforded by the spacer unit as well as the distribution of conformers.

References [1] V. P. Panov, et al. Phys. Rev. Lett., 2010, 105, 167701 [2] D. Chen, et al. PNAS, 2013, 110, 15931-15936. [3] V. Borshch, et al. Nature Communications, 2013, 4, 2635, For a review of materials exhibiting the NTB phase: R. J. Mandle, Soft Matter, 2016, 2016, 12, 7883-7901 [4] R. J. Mandle et al., Scientific Reports, 2016, 6: 36682

Chiral Columns from Achiral Chromonic Mesogens and the Formation of a New Layered Chromonic Phase

Mark R. Wilson*, Martin Walker

Department of Chemistry, Durham University, Lower Mountjoy, Stockton Road, Durham, DH1 3LE, UK E-mail: [email protected]

Results are presented from a dissipative particle dynamics (DPD) model of the phase behaviour of the non-ionic chromonic molecule TP6EO2M (below) in water, together with TP6EO2M variants where the poly(ethylene glycol) chain is replaced by a short hydrophobic–lipophobic chain. The models demonstrate the formation of supramolecular aggregates in which the hydrophobic– lipophobic chains are excluded from water by the joining together of single molecule chromonic stacks into dimers or trimers. At high concentrations, these aggregates form chromonic N and M phases and, in the case of a “Janus mesogen” (with three hydrophobic–lipophobic chains on one side of the molecule), form a novel smectic chromonic phase not previously seen experimentally or theoretically. Spontaneous symmetry breaking is observed in self-assembled columns composed of trimer stacks. Here, achiral molecular aggregates develop a spontaneous twist, inducing the formation of either left-handed or right-handed chiral aggregates. On the long time-scales accessible to DPD simulations, chiral aggregates are found to be dynamic structures in which chirality inversion can take place over long periods of time.

Left: The structure of TP6EO2M and a snapshot of a simulation box containing the chromonic nematic (N) phase formed when a single poly(ethylene glycol) chain is replaced by a short hydrophobic–lipophobic chain. Right: Self-assembled chiral columns formed from achiral molecules.

References [1] M. Walker, M. R. Wilson, Soft Matter, 2016, 12, 8588-8594. [2] M. Walker, A. J. Masters, M. R. Wilson, Phys. Chem. Chem. Phys., 2014,16, 23074-23081

DNA Nanostructures and Chromonic Liquid Crystals

Bingru Zhang1), Kevin Martens2), Luisa Kneer2), Timon Funck2), Caroline Hartl2) , Susanne Kempter2), Eva-Maria Roller2), Tim Liedl2) and Heinz-S Kitzerow1)

1)Department of Chemistry and Center for Optoelectronics and Photonics Paderborn, University of Paderborn, Warburger Str. 100, 33098 Paderborn, Germany 2)Faculty of Physics, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany E-mail: [email protected]

Liquid crystals have found increasing interest in the field of photonics and metamaterials research [1]. They may not only serve as a tunable dielectric component, but can also be used to control the position of colloidal particles. For example, colloidal particles were observed to form linear chains (Fig. 1) in the columnar phase of the lyotropic chromonic liquid crystal disodium cromoglycate (DSCG) [2]. Recently, it was confirmed that plasmonic DNA-origami nanostructures can be dissolved in lyotropic chromonic liquid crystals [3].

In addition to these finding, the poster describes the synthesis of an 18-helix- bundle DNA-origami, the hybridization with Gold-nanorods (Fig. 2) and some important parameters for embedding the DNA nanostructure in DSCG solutions, for example, the influence of pH-value and cation concentration on the phase diagram of DSCG [4].

Figure 1: Columnar phase of a DSCG- Figure 2: Transmission electron micrograph of water mixture with embedded colloidal a DNA origami nanostructure decorated particles. with a gold nanorod.

References

[1] H.-S. Kitzerow, “Photonic Micro- and Nanostructures, Metamaterials”, Handbook of Liquid Crystals (2nd edition), edited by John W. Goodby, Peter J. Collings, Takashi Kato, Carsten Tschierske, Helen Gleeson, and Peter Raynes, Vol. 8, Chapter 13, 373-426, Wiley- VCH, Weinheim, 2014 [2] N. Zimmermann, G. Jünnemann-Held, P.J. Collings, and H.-S. Kitzerow, “Self-organized assemblies of colloidal particles obtained from an aligned chromonic liquid crystal dispersion”, Soft Matter 2015, 11, 1547-1553 [3] K. Martens, T. Funck, S. Kempter, E.-M. Roller, T. Liedl, B.M. Blaschke, P. Knecht, J. A. Garrido, [4] B. Zhang and H.-S. Kitzerow, “Alignment and graphene-assisted decoration of lytropic chromonic liquid crystals containing DNA origami nanostructures”, Small 2016, 12, 1658-1666 [5] B. Zhang and H.-S. Kitzerow: “Influence of Proton and Salt Concentration on the Chromonic Liquid Crystal Phase Diagram of Disodium Cromoglycate Solutions: Prospects and Limitations of a Host for DNA Nanostructures”, J. Phys. Chem. B 2016, 120, 3250-3256

Gelled Lyotropic Liquid Crystals

Sonja Dieterich, Frank Giesselmann*, Thomas Sottmann

Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany E-mail: [email protected]

Gelled lyotropic liquid crystalline phases are soft materials in which the anisotropy of a lyotropic liquid crystal (LLC) is combined with the mechanical stability of a gel. We here present first results obtained by a systematical investigation of the preparation, the phase behaviour and the structural properties of this new class of complex fluids. The studied LLC system consists of sodium dodecylsulphate (SDS) as surfactant, decanol as co-surfactant and water. At constant temperature (25°C) and fixed water content (70 wt.%) various liquid crystalline phases (lamellar La, nematic Nd and Nc, hexagonal H1) are formed depending on the decanol to SDS ratio. Using the low molecular weight organogelator 12-hydroxyoctadecanoic acid, we developed a procedure for the simultaneous formation of the LLC phase and the gel network which leads to anisotropic and highly viscous gels (see Figure 1a). First small angle neutron scattering (SANS) studies of a gelled lamellar phase showed a higher translational order compared to its non-gelled counterpart while the layer spacing remains unchanged (see SANS data in Figure 1b). We will discuss how the gel network influences structure and properties of the lyotropic liquid crystalline phase and vice versa.

a) b)

Figure 1: a) Pictures of the gelled lyotropic lamellar phase without (left) and between (right) crossed polarizers. The gel shows no flow but strong optical birefringence. b) SANS profiles of the non-gelled lamellar phase of the system D2O – n- decanol – SDS (triangle) and the corresponding gelled lamellar phase containing 1.5 wt.% gelator (squares).

The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG Gi 243/9-1) and Fonds der Chemischen Industrie (FCI). We thank Ralf Schweins for his help with the SANS experiments at the Institut Laue-Langevin (ILL) in Grenoble, France. Impact of the Solvent Concentration on the Electroclinic Effect in Chiral Lyotropic Lamellar Phases

Marc Harjung, Frank Giesselmann*

Institute of Physical Chemistry, University of Stuttgart, 70569, Stuttgart, Germany. E-mail: [email protected]

After the recent discovery of the lyotropic analogue to the thermotropic ferroelectric smectic C* (lyo-SmC*) phase [1], phase) close to its transition into the lyo- SmC* phase [2]. We now present first detailed investigations on how the solvent content impacts on the electroclinic effect in chiral lamellar phases. We performed temperature dependent electro-optic measurements of the electroclinically induced tilt angle in two lyotropic systems) with a to lyo-SmC* phase transition (Fig. 1). Similar to the thermotropic case [3,4] it is found that the magnitude of the electroclinic coefficient depends on two factors: (i) the nature of the underlying phase transition from to lyo-SmC* phase and (ii) the magnitude of the spontaneous tilt in the lyo-SmC* phase. In general, the addition of solvent reduces the director tilt of the lyo-SmC* phase and changes the nature of the phase transition from first to second order. This opens the opportunity to tune electroclinic properties by the solvent content of the chiral lamellar phase.

a) b)

.

G10/formamide QL38-6/formamide

Figure 1: Temperature and concentration dependent electroclinic tilt at 2 V/m close to the transition from the phase into the lyo-SmC* phase: a) The G10/formamide system shows weak electroclinic coupling at low solvent content (red curve). By the addition of solvent the phase transition is shifted to second order and thus the electroclinic tilt increases (green curve). By further addition (blue curve) the magnitude of the spontaneous tilt in the underlying lyo-SmC* phase decreases and the electroclinic tilt again is reduced. b) The amphotropic QL38-6/formamide system with SmC* phase in the neat material behaves similar and shows weaker impact of the solvent.

8

6 6

4 [°] [°] 4

2 2

0 formamide 0 formamide 0 1 2 3 4 5 6 0 1 2 3 4 5 T-T [K] c T-Tc [K]

We thank Dr. Christopher P. J. Schubert (Univ. Of Waterlloo, Canada) for the QL38-6 materia.

References: [1] J. R. Bruckner, J. H. Porada, C. F. Dietrich, I. Dierking, F. Giesselmann, Angew. Chem. Int. Ed. 2013, 52, 8934-9837. [2] M. D. Harjung and F. Giesselmann, 2016, Joint Conference of the British & German Liquid Crystal Societies, Edinburgh. [3] S. Garoff and R. B. Meyer, Phys. Rev. Lett., 1977, 38, 848-851. [4] Ch. Bahr and G. Heppke, Liq. Cryst. 1987, 2, 825-831.

New Amphiphiles Forming the Lyotropic Analogue of the Thermotropic SmC* Phase

Friederike Knechta, Frank Giesselmanna*, Marc Harjunga, Christopher P. J. Schubertb, Jan H. Poradaa

aInstitute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany bDepartment of Chemistry, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada E-mail: [email protected]

The first example of the lyotropic analogue of the thermotropic SmC* phase was reported in 2013.[1] So far there is only amphiphile 1 (Fig. 1) known which forms this rare phase with water and formamide as solvent. In order to find new amphiphiles forming the lyotropic SmC* phase our design strategy shown in figure 1 was on one hand lengthening the hydrophilic spacer (JP003/JP002) and on the other hand a core exchange to a stronger SmC promoting fluorenone core (QL38-6) and further modification on the hydrophobic tail (QL38-4/5, QL41-6).

Figure 1: Design strategy based on the first known amphiphile 1 which forms a lyotropic SmC* phase with water and formamide. The first route was to lengthen the ethylene glycol spacer. The second was to exchange the core to a stronger SmC promoting fluorenone core. Based on QL38-6 the hydrophobic tail was modified.

In the neat state JP003 shows a monotropic SmA phase. In contrast to the known diol 1 the lyotropic analogue to the thermotropic SmC* phase is merely formed in the JP003/water system and not at all with formamide. A further lengthening to JP002 leads to a complete absence of the lyotropic SmC phase. The core exchange leads to the amphotropic material QL 38-6 with a SmA and SmC phase in the neat thermotropic state. It is the only fluorenone material in Fig. 1 which forms an enantiotropic lyotropic SmC phase with water as well as with formamide. In conclusion, the lyotropic SmC phase is sensitive to even very small variations in the amphiphilic structure. Based on our design strategy we enlarged the library of amphiphiles forming the very rare lyotropic analog to the thermotropic SmC* phase to three amphiphiles.

References: [1] J. Bruckner et al., Angew. Chem. Int. Ed. 2013, 52, 8934-8937.

Columnar Inclusions in Lamellar Bodies

C C Lakey*, M S Turner Department of Physics, University of Warwick, CV4 7AL, Coventry, UK E-mail: [email protected]

Multi-lamellar stacks of phospholipid membranes appear in many living organisms (e.g. in plant chloroplasts). These membranes can be composed of a mixture of saturated and unsaturated phospholipids, and cholesterol. When reduced to sufficient temperature, the mixture separates into liquid-disordered (containing mostly unsaturated lipids) and liquid-ordered (containing higher levels of saturated lipids and cholesterol) phases, which can coexist. [1] It has been observed that these liquid- ordered domains align across the multi-layer system, resulting in columnar ordering of liquid-ordered phases across many neighbouring membranes. [2] These stacks of membranes can be naturally modelled as smectic liquid crystals. The nature of the liquid-ordered regions as being relatively static and much less flexible than the surrounding liquid- disordered region, invites us to consider the liquid-ordered region as an inclusion within the smectic. Inclusions such as these can deform the arrangement of layers within the lamellar body by locally fixing the spacing between neighbouring membranes. [3] We construct a general Hamiltonian for the system, using the Landau de-Gennes Hamiltonian to account for the energy of the bulk. [4] This is used to determine the energy required to form liquid- ordered columns in the smectic. We show that columns of the kind observed can be stable, despite their locally distorting the layer spacing of the lamellae.

References [1] T. Hoshino, S. Komura, D. Andelman, The Journal of Chemical Physics 2015, Volume 143 (24), 243124 [2] L. Tayebi, Y. Ma, D. Vashaee, G. Chen, S. K. Sinha, A. N. Parikh, Nature Materials 2012, Volume 11, 1074-1080 [3] P. Sens, M. S. Turner, Journal de Physique II 1997, Volume 12, 1855-1870 [4] M. S. Turner, P. Sens, Physical Review E 1997, Volume 55 (2), R1275

Hybrid Peptide/OPV Star-Mesogens

Martin Lambov, Matthias Lehmann*

Institute of Organic Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany E-mail: [email protected]

The self-assembly of shape-persistent star mesogens has been recently shown to be tunable by guest molecules.[1,2] Thereby, the mesogens with bound ‘’pseudo’’ guests (1a-c) reveal the highest mesophase stability, since the guests cannot escape from the intrinsic cavity.[2] In order to study the impact of guests, which will not naturally incorporate to form a supermesogen by supramolecular interactions, we synthesized mesogens 2. These compounds are hybrid mesogens between different peptides and the shape-persistent conjugated star scaffold. The mesomorphic properties are studied by means of polarized optical microscopy, differential scanning calorimetry and X-ray diffraction.

References [1] M. Lehmann, P. Maier, Angw. Chem. Int. Ed. 2015, 54, 9710-9714; Angw. Chem. 2015, 127, 9846-9850. [2] M. Lehmann, P. Maier, M. Grüne, M. Hügel, Chem. Eur. J. 2017, 23, 1060-1068.

Novel Amino Acid/Crown Ether Hybrid Materials: How Charge Affects Mesomorphic Properties

Korinna Bader, Sabine Laschat*

Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany E-mail: [email protected]

Ionic Liquid Crystals (ILCs) combine the properties of ionic liquids, such as adjustable polarity and solubility, low flammability, low vapor pressure and wide electrochemical window, as well as properties of liquid crystals (LCs), such as birefringence and orientational order in the mesophase. The insertion of a stereogenic centre leads to chiral ILCs, which have a broad range of applications, including asymmetric synthesis, chiral chromatography and stereoselective polymerization. [1] The easiest way to insert a stereogenic centre is to start from chiral compounds, such as amino acids. Amino acids, as naturally occurring chiral compounds, are attractive building blocks for thermotropic and lyotropic LCs, due to their low price and good availability. Therefore, amino-acid-based LCs are well known and have been intensively investigated. [2, 3] For example, L-Tyrosine-derived ILC 1 showed broad SmA- phases. [3] On the other hand crown ethers are also successful candidates for the exhibition of mesophases and their ability to complex cations makes them suitable for various applications. [4] Furthermore, crown ethers possess a high structural diversity, because both discotic as well as calamitic molecular architectures could be realized. Whereas discotic crown ether 2 showed columnar phases, there are also numerous calamitic crown ethers, which show smectic or nematic phases. [5,6] However, mesogenic hybrid systems combining amino acids and crown ethers have not been reported up to now. Such hybrid molecules would be highly attractive, because the combination of units with different polarity and the possibility to add charges at different parts should give access to a broad range of different mesomorphic behaviour.

1 2

References [1] M. Mansueto, W. Frey, S. Laschat, Chem. Eur. J. 2013, 19, 16058-16065. [2] K. Fujimura, T. Ichikawa, M.Yoshio, T. Kato, H. Ohno, Chem. Asian J. 2016, 11, 520-526. [3] M. M. Neidhardt, M. Wolfrum, S. Beardsworth, T. Wöhrle, W. Frey, A. Baro, C. Stubenrauch, F. Giesselmann, S. Laschat Chem. Eur. J. 2016, 22, 16494-16504.

[4] M. Kaller, A. Baro, S. Laschat, in Handbook of Liquid Crystals, 2nd ed., Wiley-VCH, Weinheim, 2014, 6, 335-376. [5] M. Kaller, P. Staffeld, R. Haug, W. Frey, F. Giesselmann, S. Laschat, Liq. Cryst. 2011, 38, 531-553. [6] G.-H. He, F. Wada, K. Kikikawa, T. Matsuda, J. Chem. Soc. Chem. Commun. 1987, 1294-1296. Solid Phase Synthesis of Oligobenzoate and Peptide Amphiphiles and the Preparation of New Peptide Star Mesogens

Katrin Bahndorf, Matthias Lehmann*

Institute of Organic Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany *E-mail: [email protected]

Oligobenzoate arms 1 (Figure) are often applied in the design of calamitic, banana and star mesogens.[1] In case of larger oligobenzoate arms, consisting of a number of repeating units, solid phase assisted synthesis is of advantage over a conventional synthesis in solution.[2] The isolation of the final product is significantly simplified avoiding sophisticated extractions or column chromatography, especially when the nature of peripheral chains are varied.[2,3] This technique is also beneficial for the preparation of oligopeptide arms decorated with peripheral alkoxy chains. A β-alanine unit as the first amino acid enables the threefold coupling of such arms to a phloroglucinol core (2) furnishing oligopeptide stars, with peripheral flexible chains. Here we present the preparation of a library of star oligopeptides – among others incorporating pyrene as a probe (3a/b) to allow the investigation of the self-assembly by fluorescence spectroscopy. The mesomorphic properties of all compounds are studied by polarized optical microscopy (POM), differential scanning calorimetry (DSC), FT-IR-spectroscopy and X-ray scattering.

Figure: Oligobenzoate arms and the C3-symmetric oligopeptide star mesogens.

References [1] M. Lehmann, M. Jahr, Comprehensive Nanoscience and Technology 2011, 5, 277-357. [2] F. Guillier, D. Orain, M. Bradley, Chem. Rev. 2000, 100, 2091-2158. [3] M. Lehmann, K. Bahndorf, M. Ohnemus, S. Roth, S. Gloza, Liquid Crystals 2015, 42, 1444-1449.

Rationalizing the Impact of Subtle Structural Differences on the Properties of Hydrogen-Bonded Assemblies

1 1* 2 3 M. Pfletscher , M. Giese , C. Wölper M. Mezger

1Institute of Organic and 2Inorganic Chemistry, University of Duisburg-Essen, Universitätsstraße 7, 45141 Essen, Germany 3Institute of Physic, Johannes Gutenberg-University Mainz and Max-Planck-Institute for Polymer Research, Ackermannweg 10, 55021 Mainz, Germany E-mail: [email protected] In recent years, Supramolecular Chemistry has become a powerful tool to create functional materials. Since the macroscopic properties of such materials are closely related to their supramolecular architecture, a comprehensive understanding of these non-covalent interactions is necessary to design and synthesize new supramolecular materials in a rational manner. [1] Supramolecular liquid crystals are functional assemblies showing structural complexity as well as molecular order [2] and so far, just a few examples employing hydrogen bonds to create mesogenic assemblies are reported. [3]

Figure 1. The design of novel materials can be easily achieved using a modular concept based on non- covalent interactions (Lego brick principle). The application of such a concept simplifies the synthetic complexity and offers a facile recover of the building blocks. It is a crucial step to understand the structure-property relationships of hydrogen-bonded assemblies to design new materials.

We have prepared a series of liquid crystalline assemblies bearing functional groups that determine the macroscopic properties, such as photo-switchability or luminescence.[4] The employed modular concept (Lego brick principle) discloses an access to systematic studies, which allow to specifically investigate changes in the self-organization processes of hydrogen-bonded aggregates (red and blue moieties). Therefore, a series of supramolecular liquid crystals (Figure 1) were synthesized with small modifications of the core unit and the inserted side chains in order to understand the structure-property relationships and to achieve improved liquid crystallinity. In recent studies, we could show that the position and number of hydroxyl groups in the core unit and the nature of the linker groups (X, Y) in the side chain determine the entire structure influencing the molecular order in the mesophase.[5, 6]

References [1] T. Kato, N. Mizoshita, K. Kishimoto, Angew. Chem. Int. Ed. 2006, 45, 38-68. [2] X. Yan, F. Wang, B. Zheng, F. Huang, Chem. Soc. Rev. 2012, 41, 6042-6065. [3] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139-1241. [4] M. Pfletscher, C. Wölper, J. S. Gutmann, M. Mezger, M. Giese, Chem. Commun. 2016, 52, 8549- 8552. [5] M. Pfletscher, S. Hölscher, C. Wölper, M. Mezger, M. Giese, Angew. Chem. 2017, in progress. [6] M. Pfletscher, M. Mezger, M. Giese, ChemistrySelect 2017, in progress. Fluorination of Liquid Crystals and Self-Assembly in Confined Spaces – Towards Functional Hybrid Materials

1 1 2 2 1 Matthias Spengler, Michael Giese, * Ronald Y. Dong, Carl A. Michael, Michael Pfletscher

1University of Duisburg-Essen (Institute of Organic Chemistry, 45141 Essen, German) 2University of British Columbia (Department of Physics and Astronomy, Vancouver, Canada). E-mail: [email protected] Molecular self-assembly has attracted much attention as a bottom-up method for new functional materials.[1] The supramolecular approach is especially attractive, since it facilitates synthetic routes and yields dynamic functional aggregates combining properties of the individual building units with properties induced by the formation of the supramolecular entity.[2,3] However, self-assembly in confined spaces strongly differs from the processes in open spaces and just a few studies on the self- assembly in confined spaces, especially of LC materials, have been carried out.[4-6]

Figure 1. The design of novel functional materials with tailor-made properties can be easily achieved by using a modular approach based on the combination of different core units (red) and side chains (blue) yielding assemblies with liquid crystalline properties (POM images, left). Incorporation of these assemblies into the pores of chiral nematic mesoporous organisilica host materials gives composite materials with remarkable thermochromic and photo-responsive properties.

A series of photo-responsive hydrogen-bonded liquid crystals with different fluorination patterns have been synthesized using a modular approach that was recently reported by our group in order to investigate the impact of fluorination on the mesomorphic properties of supramolecular liquid crystals (Fig. 1).[7] The modularity allows for a systematic screening of the numerous combinations of core units (red) and side chains (blue) and helps to get insight into the self-organization processes of these aggregates. Infiltration of chiral nematic mesoporous organosilica films with the formed liquid crystalline aggregates yielded supramolecular composites with remarkable photonic, thermochromic and photo-responsive properties upon heating and cooling.

References [1] K. Liu, Y. Kang, Z. Wang and X. Zhang, Adv. Mater., 2013, 25, 5530-5548. [2] X. Yan, F. Wang, B. Zheng and F. Huang, Chem. Soc. Rev., 2012, 41, 6042-6065. [3] Z.-T. Li and L.-Z. Wu, Hydrogen-Bonded Supramolecular Materials, Springer, Heidelberg, 2015. [4] M. Giese, T. Krappitz, R. Y. Dong, C. A. Michal, W. Y. Hamad, B. O. Patrick, M. J. MacLachlan, J. Mater. Chem. C, 2015, 3, 1537-1545. [5] Z. Ghattan, T. Hasek, R. Wilk, M. Shahabadi, M. Koch, Opt. Commun., 2008, 281, 4623–4625. [6] M. Giese, J. C. de Witt, K. E. Shopsowitz, A. P. Manning, R. Y. Dong, C. A. Michal, W. Y. Hamad, [7] M. J. MacLachlan, ACS Appl. Mater. Interfaces, 2013, 5, 6854–6859. [8] M. Pfletscher, C. Wolper, J. S. Gutmann, M. Mezger and M. Giese, Chem. Commun., 2016, 52, 8549-8552.

Structural Changes upon Heating Tristriazolotriazines

Thorsten Rietha, Nico Rödera, Frédéric Laquaic, Matthias Lehmannb, Heiner Deterta*

aInstitute for Organic Chemistry, University of Mainz, Duesbergweg 10–14, 55099 Mainz bInstitute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg cKing Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia E-mail: [email protected]

The threefold Huisgen reaction [1]of cyanuric chloride and alkoxyphenyl tetrazoles gives tristriazolotriazines 1a-h, fluorescent -conjugated molecules. The phenyl rings are tangentially attached tristriazolotriazine, the torsion angles between triazole and phenyl are 12 – 82°,[2] giving a paddle-wheel structure to these discotic molecules. The melting point of triphenyl-TTT is above 300 °C, but two or three alkoxy chains of medium length result in the formation of broad mesophases, typically with a hexagonal columnar structure [3, 4] and often a complex superstructure.[5] Contrary to earlier reports,[3] these DLCs are not thermostable. A rearrangement of the TTT unit occurs in three successive steps, bringing the phenyl substituents from the tangential positions in 1 to radial positions as in 2. The new r-TTT is nearly planar. The extension of the molecular diameter and the planarization has a huge impact on the thermotropic properties: higher melting points, complete loss of mesomorphism, but also the transformation of non-mesomorphous t-TTTs to discotic liquid crystals has been observed.

References [1] R. Huisgen, H.J. Sturm, M. Seidel, Chem. Ber. 1961, 94, 1555-1562 [2] K. Herget, D. Schollmeyer, H. Detert, Acta Cryst. 2013, E69 o365-o366. [3] R. Cristiano, H. Gallardo, A. J. Bortoluzzi, I. H. Bechtold, C. E. M. Campos, R. L. Longo, Chem. Commun. 2008, 5134-5136. [4] S. Glang, V. Schmitt, H.Detert, Proceedings of 36th German Topical Meeting on LiquidCrystals 2008, 125-128. [5] T. Rieth, T. Marszalek, W. Pisula, H. Detert, Chemistry 20 2014 5000 – 5006.

Pyrazine Based, Thermotropic Liquide Crystals with St. Andrew’s Cross Shape: Synthesis, Optical and Thermotropic Properties

N. Tober, N. Röder, H. Detert*

Institut für Organische Chemie, Johannes Gutenberg-Universität, Duesbergweg 10-14, 55128, Mainz, Germany E-mail: [email protected]

Pyrazines are rarely applied as building blocks in liquid crystals yet.[1] We report new discotic pyrazines with broad mesophases showing the characteristic textures of a columnar arrangement observed by polarisation optical microscopy. The synthesis of new St. Andrew’s cross like 2,3,5,6-tetraphenylpyrazines were performed by cyclisation of 4,4’-bis(methoxycarbonyl)benzoine with ammonium acetate followed by oxidation with iodine.[2] Those pyrazine centered -systems were enlarged by additional Huisgen[3] reaction which leads to mesomorphic alkoxyaryl- substituted 2,3,5,6-tetrakis-(4-(1,3,4-oxadiazol-2- yl)phenyl)pyrazines (TOPP). We focused on synthesis and characterisation of 3,4-alkoxyphenyl substituted TOPPs. Additionally the aromatic system was increased by introduction of biphenylene and naphthalene. Further investigations of the compounds were done by optical spectroscopy, differential scanning calorimetry, single crystal X-ray scattering, wide- and small- angle X-ray scattering on orientated fibers.

Figure 1: St. Andrew’s cross shaped TOPPs (middle) with different substituents (left) and single crystal structure (right)

References [1] J. W. Brown, D. T. Hurst, J. P. O'donovan, D. Coates, J. D. Bunning, Liquid Crystals 1995, 765 – 774. [2] F. R. Japp, W. H. Wilson, J. Chem. Soc., Trans. 1886, 49, 825 – 831. [3] R. Huisgen, J. Sauer, H. J. Sturm, J. H. Markgraf, Chem. Ber. 1960, 93, 2106 – 2124.

Donor-Substituted Discotic Liquid Crystals with Branched Alkyl Chains

Daniel Limbach, Thorsten Rieth, Prof. Dr. Heiner Detert*

Institut für Org. Chemie, Johannes Gutenberg-Universität, 55128 Mainz, Germany E-mail: [email protected]

Discotic liquid crystals (DLC) with a tristriazolotriazene core (TTT) have been reported with various substituents. While there are several examples for n-alkyloxy substituted phenyl-TTTs only one DLC with branched alkyl chains is known [1-3]. Whereas the connection between chain length and LC behaviour has been studied for n-alkyloxy substituted phenyl-TTTs, TTTs with branched alkyloxy side chains are nearly unknown. To shed light on the impact of branching peripheral alkoxy The TTTs were prepared via a Huisgen-reaction of the respective tetrazoles. The substances have been characterized by NMR- and mass spectroscopy. Liquid crystalline behaviour has been studied via polarisation microscopy and differential scanning calorimetry. 4-(2-Hexyl)-octyloxyphenyl- TTT (1) and N,N-didodecylamino-phenyl-TTT (2) show no mesomorphic phases while 4-(2-decyl)- dodecyloxyphenyl-TTT (3) and 3,4-bis(tetrahydrogeranyloxy)-phenyl-TTT (4) display typical DLC- behaviour.

Tristriazolotriazin-core (left) and TTTs without LC behaviour (1 and 2) and TTTs with LC behaviour (3 and 4)

References [1] R. Cristiano, J. Eccher, I. H. Bechtold, C.N. Tironi, A. A. Vieira, F. Molin, and H. Gallardo, Langmuir, 2012, 28, 11590–11598. [2] A. G. Dal-Bó, G. G. López Cisneros, R. Cercena, J. Mendes, L. M. da Silveira, E. Zapp, K. G. Domiciano, R. da Costa Duarte, F. S. Rodembusch, T. E. A. Frizon, Dyes and Pigments, 2016, 135, 49-56. [3] S. Glang, T. Rieth, D. Borchmann, I. Fortunati, R. Signorini, H. Detert, Eur. J. O. Chem. 2014, 2014, 3116-3126.

Oligo(ethyleneoxy) Chains and their Impact on the Self-Assembly of Star-shaped Donor-Acceptor Mesogens

Markus Hügel, Matthias Lehmann*

Institut für Organische Chemie, Julius-Maximilians-Universität Würzburg, Germany Email: [email protected]

The control over the clearing temperature is an important factor when it comes to the application of liquid crystals in organic electronics. The macroscopic alignment, which significantly improves the desired physical properties, is frequently achieved from the isotropic melt of the material.[1,2] Compounds 1 - 3 assemble in remarkable helical structures along their columnar axes, which are attractive for the application in photovoltaic cells, but they decompose slowly at elevated temperatures. Therefore, we sought a strategy to lower the clearing points for these materials.[3] Here we report on the dramatic change of the self-assembly when substituting the dodecyloxy chains with oligoethyleneoxy chains. The synthesis of the parent molecules and their derivatives as well as the change in clearing temperatures or nature of the phases will be discussed. The presented results are supported by studies of polarised optical microscopy, solid state NMR spectroscopy and X-ray scattering.

Structures of the star-shaped mesogens with potential applications in organic electronics

References [1] E. Grelet et al., Chem. Phys. Lett. 2009, 476, 89-91. [2] Y. Geerts, S. Sergeyev, W. Pisula, Chem. Soc. Rev. 2007, 36, 1902-1929. [3] M. Lehmann, M. Hügel, Angew. Chem. Int. Ed. 2015, 54, 4110-4114. Phthalocyanine Hybrid Star Mesogens – New Materials for Potential Photovoltaic Applications

Moritz Dechant, Matthias Lehmann*

Institut für Organische Chemie, Julius-Maximilians-Universität Würzburg, Germany Email: [email protected]

Star-shaped oligo(p-phenylenevinylene) compounds are nonconventional shape-persistent mesogens, which form liquid crystalline mesophases despite the large void space between their arms (Figure 1).[1] Four-armed phthalocyanine stars with terminal oligoethyleneoxy chains 1 (X = H) exhibit hexagonal columnar LC- phases over broad temperature ranges by nanosegregation of the rigid core and the long lateral chains. Phthalocyanines are highly interesting substances for the application in organic photovoltaic cells due to their strong absorption in the red- and infrared range and their flat and broad -system, which allows efficient -stacking along columnar assemblies.[2] [3] Analogous to previous studies, fullerenes are covalently linked via short spacers to the stilbene arms in order to fill the void and stabilize the mesophase.[4] This design should result in the segregation of fullerene acceptor and phthalocyanine/stilbene donor scaffolds and result in a spatially separated donor-acceptor column. The highly ordered, liquid-crystalline structures are investigated by means of polarized optical microscopy, differential scanning calorimetry and comprehensive X-ray scattering.

R = O(C H O) C H

2 4 3 2 5

n = 0,1,2

X = H,

Free space

References [1] M. Lehmann, B. Schartel, M. Hennecke, H. Meier, Tetrahedron 1999, 55, 13377 – 13394 [2] R. Enes, J. Cid, A. Hausmann, O. Trukhina, A. Gouloumis, P. Vázquez, J. Cavaleiro, A. Tomé, D. M. Guldi, T. Torres, Chemistry – A European Journal 2012, 18, 1727-1736. [3] P. Apostol, J. Eccher, M. E. R. Dotto, C. B. Costa, T. Cazati, E. A. Hillard, H. Bock, I. H. Bechtold, Physical Chemistry Chemical Physics 2015, 17, 32390-32397. [4] M. Lehmann, M. Hügel, Angewandte Chemie International Edition 2015, 54, 4110-4114.

Crown Ether Based Discotics with Branched Side Chains

Robert Forschner[a], Sabine Laschat*[a], Jochen Kirres[a], Friederike Knecht[b], Philipp Seubert[a], [a] Angelika Baro

[a] Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70563 Stuttgart [b] Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70563 Stuttgart E-mail: [email protected]

Discotic liquid crystals show attractive properties which make them suitable for applications in electronic devices, such as organic light-emitting diodes (OLEDs), sensors, or organic field-effect transistors (OFETs).[1] Crown ether-based mesogens are promising candidates for these purposes, because of their structural variety like crown size, symmetry, and salt complexation. Systematic studies of o-terphenyl- 1 and triphenylene-substituted derivatives 2 carrying peripheral linear side chains were performed, however ambient temperature mesophases could not be achieved.[2] To overcome this temperature problem, 15-crown-5 derivatives with branched side chains of varying length were synthesized and studied by differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). Columnar hexagonal mesophases at room temperature for all derivative with δ-methyl branched side chains was observed. Additionally, the branching resulted in an increased mesophase width up to 147 K, compared to linear side chains.[3] a)

b)

Figure: a) Structure of o-terphenyl 1 and triphenylene 2 derivatives, b) oriented SAXS pattern of 2 with δ-methyl branched side chains (n = 6).

References [1] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139–1241. [2] M. Kaller, P. Staffeld, R. Haug, W. Frey, F. Giesselmann, S. Laschat, Liq. Cryst. 2011, 38, 531–553. [3] M. Kaller, S. J. Beardsworth, P. Staffeld, S. Tussetschläger, F. Gießelmann, S. Laschat, Liq. Cryst. 2012, 39, 607–618. [4] J. Kirres, F. Knecht, P. Seubert, A. Baro, S. Laschat, ChemPhysChem 2016, 17, 1159–1165.

Liquid Crystal Dendrimers of Star-Shaped Triphenylbenzenes

Andrea Bühlmeyer, Abdirashid Obsiye, Tobias Wöhrle, Johannes Christian Haenle, Sabine Laschat*

Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany. E-mail: [email protected]

In the last decades much progress has been achieved in the research of discotic liquid crystals, regarding novel tailor made materials towards a possible application in electronics (e.g. organic semiconductors) and optoelectronics (e.g. photovoltaic devices). [1] Due to their non-planar structure triphenylbenzene (TPB) were thought unsuitable as core molecules for liquid crystals. [2] Recently our working group discovered that TPBs show liquid crystalline behaviour in dependence on their degree of substitution, where hexa-substituted TPBs show no mesophase while nona- substituted TPBs display broad mesophases. Trough XRD investigations a helical stacking was indicated which would compensate the non-planar TPB core system. [3] In a further approach we enlarged the substituents on the TPBs to gain further insight in the mesophase arrangements of TPBs and the driving forces between bulky side groups. [4]

a) Schematic helical structure of the TPB with rotating phenyl groups and b) a nona-substituted TPB

References [1] T. Wöhrle, I. Wurzbach, J. Kirres, A. Kostidou, N. Kapernaum, J. Litterscheid, J.C. Haenle, P. Staffeld, A. Baro, F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139-1241. [2] E. Frackowiak , G. Scherowsky, Z. Naturforsch 1997, 1539-1543. [3] T. Wöhrle, S. J. Beardsworth, C. Schilling, A. Baro, F. Giesselmann, S. Laschat, Soft Matter 2016,12, 3730-3736. [4] A. Obsiye, T. Wöhrle, J. C. Haenle, A. Bühlmeyer, S. Laschat, Manuscript in preparation. Crowded Star Mesogens: Guest Controlled Stability of Mesophases from Unconventional Liquid Crystal Molecules

Philipp Maier, Matthias Lehmann*

Institute of Organic Chemistry, University of Würzburg, Am Hubland, 97074 Würzburg, Germany E-mail: [email protected]

Hexa-substituted, shape-persistent benzenes are sterically crowded star molecules which are rarely found to form liquid crystalline phases owing to their non-planar core geometries.[1] However, compounds 1-3 based on oligo(phenylenevinylene) arms exhibit stable columnar liquid crystalline phases. The alternating substitution around the benzene core generates free space between the conjugated arm scaffolds. Such structures allow the inclusion of additional guest molecules. Mesogen 1 forms a double helical columnar mesophase, which is strongly stabilized by dipole-dipole interactions of the pyridyl moieties and the filling of free space.[2] The pyridyl units are potential hydrogen bond acceptors and these binding sites accept carboxylic acids in the supramolecular compounds 2a-c exhibiting mesophases of not much lower stability than 1. The attachment of guests via covalent ester functions in 3a-c increases the clearing temperatures by more than 100 °C, while physical mixtures with a methyl ester leads to clearing temperatures below 100 °C.[3] Evidently, the mesophase stability can be controlled by the binding mode of the arylcarboxy groups. In this presentation the origin of the variation in clearing temperature is unraveled by DSC, Xray diffraction, modelling, cohesive energy density considerations and solid-state NMR spectroscopy.

Figure 1: Supramolecular and covalent star-shaped hexasubstituted mesogens.

References [1] H. Detert, M. Lehmann, H. Meier, Materials 2010, 3, 3218-3330. [2] M. Lehmann, P. Maier, Angew. Chem. Int. Ed. 2015, 54, 9710-9714. [3] M. Lehmann, P. Maier, M. Grüne, M. Hügel, Chem. Eur. J. 2017, 23, 1060-1068.

Influence of Molecular Chirality on the Cubic and Isotropic Liquid Phases of Polycatenar Molecules

Tino Reppe, Silvio Poppe, Carsten Tschierske*

Department of Chemistry, Martin-Luther-University Halle-Wittenberg, 06120, Halle, Germany E-mail: [email protected]

Chirality synchronization of achiral molecules into macroscopic chiral superstructures in the liquid state is an emerging field with implications on emergence and amplification of chirality [1]. Especially the formation of spontaneously chiral bicontinuous cubic phases, like I432 [2] and chiral isotropic liquids [3] represent a new field to explore. Herein we report a new series of polycatenar compounds based on 5,5´-diphenyl-2,2´-bithiophene, with a racemic or enantiomerically pure terminal chain unit. These compounds were synthesised and characterised by polarizing microscopy, differential scanning calorimetry and XRD (Figure 1). Depending on the molecular structure two different types of bicontinuous cubic phases were observed, the achiral Ia3d phase and the chiral with space group I432, formed by the racemic as well as the uniformly chiral compounds. Above the cubic phases of the racemates there appears either an achiral isotropic liquid (Iso) or a chiral conglomerate liquid (Iso1[*]), while all enantiomerically pure molecules show a homochiral Iso1* phase which continuously becomes almost achiral with rising temperature, indicating the presence of a local helical structure in the liquids occurring besides the cubic phases.

Figure 1: Structure of discussed polycatenar liquid crystals (n = 6, 10 and m = 0, 1)

References [1] C. Tschierske G. Ungar, ChemPhysChem 2016, 17, 9-26 [2] C. Dressel, F. Liu, M. Prehm, X. Zeng, G. Ungar, C. Tschierske, Angew. Int. Ed. 2014, 53, 13115- 13120; M. Alaasar, M. Prehm, Y. Cao, F. Liu, C. Tschierske, Angew. Chem. Int. Ed. 2016, 55, 312-316 [3] C. Dressel, T. Reppe, M. Prehm, C. Tschierske, Nature Chem. 2014, 6, 971-977 Cubic and Non-Cubic Phases of -Shaped Bolapolyphiles

Silvio Poppe1, Alexander Scholte, Feng Liu2 and Carsten Tschierske1

1Institute of Chemistry, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Str. 2, 06120 Halle, Germany 2Xi’an Jiaotong University, Xi’an 710049, P. R. China E-mail: [email protected]

T-shaped and X-shaped bolapolyphiles are able to form a wide variety of new LC phases, among them various liquid crystalline honeycomb structures – with polygonal cells of different shapes ranging from triangular to hexagonal and beyond [1-4]. Herein we report a new type of -shaped polyphilic molecules, having two alkyl chains fixed to only one side of the rod-like core (Figure 1). These compounds were synthesized and their mesomorphic behaviour was fully characterised by XRD, DSC and polarizing microscopy. Depending on the chain length and side chain structure, a series of very different and highly complex new LC phases was observed. Besides columnar phases, either with square, hexagonal or rectangular lattice, two different types of cubic phases, and also correlated lamellar phases were found. The rectangular columnar phase representing honeycombs composed of octagonal and pentagonal cylinders in a ratio 1:2, leading to a tiling pattern resembling that of zeolites.[2]. With high chain lengths two cubic phases, one with Ia3¯ d lattice (bicontinuous, double gyroid) and the other with Fd3¯ m lattice (single diamond) were found. The lamellar phases occurring besides these cubic phases represent layers with the rod-like unit arranged parallel to the layer planes; correlation between adjacent layers leads to the observed p2mm symmetry. The self- assembly of the - shaped molecules will be compared and discussed in relation to related compounds with the two chains at opposite sides of the aromatic core (X-shaped) and those with only one linear or branched chain (T-shaped) with the same volume as the two chains.

Figure 1: -shaped bolapolyphiles.

References [1] C. Tschierske, Angew. Chem. 2013, 125, 8992. [2] S. Poppe, A. Lehmann, A. Scholte, M. Prehm, X. Zeng, G. Ungar, C. Tschierske, Nature Commun. 2015, 6, 8637. [3] F. Liu, M. Prehm, X. Zeng, C. Tschierske, G. Ungar, J. Am. Chem. Soc., 2014, 136, 6846-6849. [4] X. Zeng, M. Prehm,G. Ungar, C. Tschierske, F. Liu, Angew.Chem. Int. Ed. 2016, 55, 8324–8327.

Four-Arm, Star-Shaped Mesogens as Precursors for Functional Liquid Crystal Materials

Sabine Roth, Matthias Lehmann*

Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany e-mail: [email protected]

Three-armed stars with a semi-flexible oligobenzoate scaffold form lamellar, 2D and 3D- columnar and cubic micellar phases by nanosegregation and efficient space- filling.[1-4] Thereby, the molecules fold to different E- or cone-shaped conformers as a function of symmetry of the benzoate scaffold. This process prevents the controlled self-assembly of chromophores incorporated at specific positions along the arms.[1] Owing to the preorganization of the arms in stars with a 1,2,4,5- tetrasubstituted scaffold, which are claimed to fold to rod-shaped mesogens,[5] such molecules would be perfect candidates to improve the self-organisation process. Therefore, we aim the synthesis of new mesogens S0-S2 with different numbers of peripheral chains. Polarized optical microscopy, differential scanning calorimetry, X-ray diffraction and molecular modelling confirm that the series of mesogens self-assemble in a broad range of different nanosegregated structures but also give evidence that rod-shaped mesogens are not the predominant conformers according to our analysis.

General structure of the target compounds and three examples of structures; left: bowl shaped (S1c), middle: smectic phase with molecular clusters (S1b), right: tilted, rod like structure in the SmC phase (S1a)

References [1] M. Lehmann. M. Jahr, B. Donnio, R. Graf, S. Gemming, I. Popov, Chem. Eur. J. 2008, 14, 3562-3576. [2] M. Lehmann, M. Jahr, F. C. Grozema, R. D. Abellon, L. D. A. Siebbeles, M. Müller, Adv. Mater. 2008, 20, 4414-4418. [3] M. Lehmann, Chem. Eur. J. 2009, 15, 3638-3651. [4] M. Lehmann, M. Jahr; Org. Lett. 2006, 8, 721–723. [5] W. D. J. A. Norbert , J. W. Goodby , M. Hird, K. J. Toyne, Liquid Crystals 1997, 22(5), 631-642.

Synthesis and Structure-Property-Relationship of Star-Shaped Crowded Mesogens with Semi-Flexible Arms

Benjamin Fröhlich, Matthias Lehmann*

Institute of Organic Chemistry, University of Würzburg, Am Hubland, D-97074 Würzburg E-mail: [email protected]

Star-shaped crowded mesogens with H-bond acceptor units have been recently shown to assemble in helical columnar phases.[1] The uptake of three guests in this LC endoreceptors results in conventional columnar phases.[1,2] These mesogens, however, consist of a shape-persistent stilbenoid scaffold. In contrast semi- flexible oligo(benzoate) star mesogens tend to fold to E- and cone-shaped conformers in columnar and cubic phases, a process which is not completely predictable.[3] The presented study explores mesogens 2, with a crowded core but semi-flexible arm scaffold in order to prevent the folding.

Figure 1: Triphenylbenzene core as precursor for star-shaped mesogens with semi-flexible arm scaffold.

The actual synthesis starts with the core unit 1 to which different building blocks can be attached progressively by divergent synthesis strategies. Especially, the condensation of the internal oxygens is highly demanding for steric reasons. However, a number of different compounds 2 could be isolated and their thermotropic properties are investigated by polarised optical microscopy (POM), differential scanning calorimetry (DSC), X-ray scattering and FTIR spectroscopy.

References [1] M. Lehmann, P. Maier, Angew. Chem. Int. Ed. 2015, 54, 9710-9714. [2] M. Lehmann, P. Maier, M. Grüne, M. Hügel, Chem. Eur. J. 2017, 23, 1060-1068 [3] M. Lehmann, M.; Star-shaped Mesogens in Handbook of Liquid Crystals, 2nd edition, Vol. 5, Chapter 5, (eds. J. W. Goodby, P. J. Collings, T. Kato, C. Tschierske, H. Gleeson, P. Raynes, Wiley-VCH, Weinheim, 2014.

Blends of Two Perylene Derivatives: Liquid Crystalline and Optoelectronic Properties

a,b a a a c a,b J. Vollbrecht *, A. Stepen , K. Nolkemper , S. Keuker-Baumann , H. Bock and H. Kitzerow

aDept. of Chemistry, Univ. of Paderborn, 33098 Paderborn (Germany). bCeOPP, Univ. of Paderborn, 33098 Paderborn (Germany). cCentre de Recherche Paul Pascal, CNRS, Univ. Bordeaux, 33600 Pessac (France). E-mail: [email protected]

In the last decade, organic semiconductors (OSC) have been investigated and used in a variety of devices, most notably organic light emitting diodes (OLED), photovoltaic cells (OPV) and field effect transistors (OFET). Increasing the charge carrier mobility of the necessary OSC nanofilms is one of the principal requirements for a ubiquitous application in the future. This can be achieved by improving the order of the OSC nanofilms. For this reason, liquid crystalline OSCs – in particular discotic and calamitic compounds – have garnered a lot of attention owing to their self- organizing properties.[1] Numerous different compounds with liquid crystalline properties have been synthesized and characterized for this purpose. Another – more recent – approach to improve the order of OSC nanofilms is to blend two compounds to combine their mesophase formation and optoelectronic properties beneficially.[2,3]

Fig. 1: Chemical structures of the investigated perylene tetraester (1) and the dinaphthocoronene tetraester (2). POM image of compounds 1 and 2 at their interface (the polarizers were slightly uncrossed; temperature T = 188 °C).

In this study, we have investigated blends of a perylene tetraester (1) and a dinaphthocoronene tetraester (2) (Fig. 1). Compound 1 was chosen due to its favorable liquid crystalline properties and compound 2 due to its optoelectronic properties. The phase diagram of the blends was studied via polarized optical microscopy (POM), differential scanning calorimetry (DSC) and x-ray diffraction (XRD). Prototype OLEDs were fabricated to test their electroluminescent and optoelectronic properties.

References [1] R. J. Bushby, K. Kawata, Liquid Crystals 2011, 38, 1415-1426. [2] Y. Li, M. G. Li, Y. J. Su, J. G. Liu, Y. C. Han, S. J. Zheng, L. X. Wang, Chinese Chemical Letters 2016, 27, 475-480. [3] J. Eccher, A. C. Batista Almeida, T. Cazati, H. v. Seggern, H. Bock, I. H. Bechtold, Journal of Luminence 2016, 180, 31-37. Chiral Nematic Droplets for Lasing: Microfluidic Generation and Manipulation

Margaret C. Normand, Konstantinos Englezopoulos, Anne C. Pawsey, Philip J.W. Hands*

Institute of Integrated Micro & Nano Systems (IMNS), School of Engineering, University of Edinburgh, Alexander Crum Brown Road, EH9 3FF Edinburgh, UK *E-mail: [email protected]

Chiral nematic liquid crystals (LC) can be used to form high quality, tuneable resonant cavities suitable for photonic band-edge lasing. This has normally been achieved by promoting a standing helix molecular structure in a glass cell, or with dried emulsions.[1] However, recent research has shown that droplets of chiral nematic LC in an immiscible host solution can also be used; the helical structure forms radially resulting in a ‘spherulite’ texture and omnidirectional laser emission.[2][3] There are several different techniques for fabricating droplets, from simple mixing of emulsions to drop-on-demand microfluidics. Not all are optimal for producing lasing droplets with consistent optical performance. We report upon the use of microfluidic channel junctions as a repeatable method of fabricating monodisperse droplets of dye-doped chiral nematic LC. We are able to study the optical properties of the droplets during formation, whist flowing in a microfluidic channel, and in storage chambers of various dimensions. We also demonstrate directional laser emission from confined, non-spherical, droplets. Our findings will be discussed in the context of enabling applications of LC laser droplets.

Figure 1 - Polarising optical microscopy of dye-doped chiral nematic LC droplets in a microfluidic channel.

References [1] D. J. Gardiner, S. M. Morris, P. J. W. Hands, C. Mowatt, R. Rutledge, T. D. Wilkinson, H. J. Coles, Opt. Express, 2011, 19, 2432–2439 [2] M. Humar, I. Musevic, Opt. Express, 2010, 18, 26995–27003 [3] M. Humar, F. Araoka, H. Takezoe, I. Muševič, Opt. Express, 2016, 24, 19237. Microtechnical Processing of Liquid Crystal Elastomers

D. Dittera, W.-L. Chenb, C. K. Oberb, H. Zappec, R. Zentela

aInstitute of Organic Chemistry, Johannes Gutenberg-University, Mainz, Germany bDepartment of Materials Science and Engineering, Cornell University, USA cInstitute for Microsystem Technology-IMTEK, Albert-Ludwigs-University, Freiburg, Germany

Liquid crystal elastomers (LCEs) combine the properties of polymeric elastomers with the self- organization of liquid crystals. Their actuation capacities through the anisotropy-to-isotropy change of macromolecular chains make them an unique class of shape memory materials, which have become attractive in microelectromechanical system (MEMS) devices.[1, 2] In this work we want to present a LCE system, that shows versatile two and three-dimensional actuation motions and a way to structure it in the micrometer range without losing their actuation properties. We developed a spin-coating process with which we can get LCE layers in the range of 300 nanometers to a couple of microns. For this we spin-coated a water soluble sacrificial layer, a photoalignment layer and a LCE formulation (Fig. 1), that was polymerised and cross-linked in its nematic liquid crystal phase by UV light, one after another on a substrate. The resulting LCE films show reversible 3-dimensional bending and twisting and 2-dimensional shrinkage and elongation actuations up to 50% between 90 and 120°C in dependence of their thicknesses. Additionally, the actuation temperature can be decreased by using a comonomer.[3]

Figure 1: Used LCE formulation (comonomer can be used for actuation temperature variations).

Furthermore, we could structure those layers in an oxygen plasma with a resolution of 1.5-2.0 microns in a photolithographic process. Up to 700 nm a single fluorinated positive photoresist layer and for thicker films another three layers with CYTOP as a second sacrificial layer and hydrogen silsesquioxane (HSQ) as a hardmask was used for this process (Fig. 2).

Figure 2: Hard mask patterning process and different LCE actuation motions.

References [1] C. Ohm, M. Brehmer and R. Zentel, Adv. Mater. 2010, 22, 3366-3387. [2] H. Yang, G. Ye, X. Wang and P. Keller, Soft Matter 2011, 7, 815. [3] D.L. Thomsen, P. Keller, J. Naciri, R. Pink, H. Jeon, D. Shenoy, B. Ratna, Macromolecules, 2001,34, 5868-5875. Tuneable, Switchable Liquid Crystal Laser Filter

Ethan I. L. Jull, Helen F. Gleeson*

School of Physics and Astronomy, University of Leeds, LS2 9JT E-mail: [email protected]

Liquid crystal tuneable Lyot filters have been implemented in many areas including astronomical observations [1], remote sensing [2], laser tuning [3] and biological imaging [4]. The underlying physics behind the operation of these devices is well understood. In this study the use of a simple and compact liquid crystal Lyot filter as a switchable laser protection device is demonstrated. The device has the ability to switch from an OFF state in which there is transmission at all wavelengths, to an ON state which rejects specific wavelengths. The switch is shown to take place in less than 110 ms, depending on the wavelength to be blocked. A tuning range between 480 nm and 640 nm is shown, with the potential to operate outside of the visible spectrum due to higher order half-wave plate conditions. With the system in the ON state the transmission at the rejected wavelength was reduced to close to zero, limited only by the polarisers extinction ratio, whilst transmission at other wavelengths allowed for partial observations even when in protection mode.

Figure Caption: (left) A schematic of a liquid crystal Lyot filter is shown. (right) The change in laser intensity when switching from the OFF state to the ON state is shown.

References [1] G. A. Kopp et al. Applied Optics 1997, 36, 291-296 [2] R. R. Seymour et al. Optical Engineering 1994, 33, 915-923 [3] H. F. Gleeson et al. Optics Communications 2002, 212, 165-168 [4] H. R. Morris et al. Applied Spectroscopy, 1994, 48, 857-866

Co-Flow Microfluidic Synthesis of Liquid Crystalline Actuating Janus Particles

Tristan Hessberger, Rudolf Zentel*, Lukas Braun

Department of Organic Chemistry, Johannes Gutenberg University, Mainz, Germany E-mail: [email protected]

Liquid crystalline elastomers (LCEs) have been studied and developed as functional materials for actuator applications, such as stimuli-responsive shape- changing microparticles.[1-3] LCEs are slightly crosslinked liquid crystalline polymers which perform a macroscopic shape transformation during the phase transition of the liquid crystalline and the isotropic state. The prerequisite for a strong shape transformation of the LCE is the uniform alignment of the liquid crystalline director over the LCE sample. A capillary based microfluidic device enables the formation of microdroplets in a highly viscous continuously flowing silicone oil. Thereby, polymerisable mesogens are oriented due to the shear rates acting on the dispersed liquid crystalline droplets. Further UV-induced polymerisation and crosslinking of the LC-monomer droplets in the nematic phase leads to actuating LCE-particles.

Formation and polymerization of Janus-droplets in the continuous flow of a capillary based microfluidic device (left). Shape change of the LCE in a Janus-particle during the thermic phase transition (right).

In this work the microfluidic synthesis and characterization of liquid crystalline actuating Janus- particles is presented.[1] On one side these Janus particles consist of a hydrophobic liquid crystalline part, featuring strong shape changes during the thermotropic phase transition, whereas the other side contains a hydrophilic polyacrylamide network. During the synthesis, two capillaries provide the phase separating monomer mixtures, forming Janus droplets which are strongly sheared in the polymerisation tube. The resultant Janus particles exhibit an elongated rod-like shape and a bipolar director field, which was observed by WAXS measurements. The particles’ actuation properties were studied via POM, in which relative length changes of the particle’s LCE up to 52% were investigated during the phase transition. Furthermore, the synthesis of actuating microparticles from a thiol-ene based main-chain liquid crystalline elastomer is presented.[2] These particles exhibit a deformation from a spherical to a rod-like shape during the phase transition, at which the particles’ aspect ratio is almost doubled. The transition temperature, the temperature range and the magnitude of the actuation are varied by altering the content of a liquid crystalline crosslinker.

References [1] T. Hessberger, L. B. Braun, F. Henrich, C. Müller, F. Gießelmann, C. Serra, R. Zentel, J. Mater. Chem. C 2016, 4, 8778-8786. [2] T. Hessberger, L. B. Braun, R. Zentel, Polymers 2016, 8, 410-421. [3] L. B. Braun, T. Hessberger, R. Zentel, J. Mater. Chem. C 2016, 4, 8670-8678.

From Cholesteric Liquid Crystal Shells to Secure Authentication

Yong Geng1, JungHyun Noh1, Gabriele Lenzini2, Romano Rupp3, Irena Drevensek-Olenik4, Jan Lagerwall1* 1University of Luxembourg, Physics & Materials Science Research Unit, 1511 Luxembourg 2University of Luxembourg, Interdisciplinary Center for Security and Trust, 2721 Luxembourg 3University of Vienna, Faculty of Physics, 1090 Vienna, Austria 4University of Ljubljana, Faculty of Mathematics and Physics, 1000 Ljubljana, Slovenia E-mail: jan.Lagerwall@lcso/ma1er.com

When confined in a spherical sample, planar-aligned short-pitch cholesteric (N*) liquid crystals give rise to peculiar optical effects that are both fascinating and useful, thanks to visible selective reflection in all radial directions. A colorful pattern appears thanks to photonic cross communication between N* spheres, and this pattern depends sensitively on the location of spheres, the area that is illuminated, and the pitch of the N* helix [1]. We prepare such samples using nested capillary microfluidics, allowing us to produce N* shells with about 100µm radius and about 10µm thickness at high throughput [2]. By polymer-stabilizing the shells they become sufficiently robust mechanically for applications of the shells to be realistic. In a cross-disciplinary physics-computer science effort we are targeting the use of collections of N* shells as unclonable tokens for secure authentication [2, 3]. A random arrangement of shells with different helix pitch ensures that each generated pattern is unique, the dynamic quality and circular polarization given by the N* structural color rendering it exceptionally difficult to reproduce.

Photonic cross communication pattern from N* shells with varying pitch.

References [1] J. Noh, H.-L. Liang, I. Drevensek-Olenik, J.P.F. Lagerwall. J. Mater. Chem. C 2014, 2, 806-810. 2. Y. Geng, et al. Sci. Rep. 2016, 6, Artnr. 26840, DOI: 10.1038/srep26840. [2] https://www.youtube.com/watch?v=KOW-Jqtb6NI

Transient Dynamics in the Accelerating Region of Collapsing Freely Suspended Films

Florian von Rüling, Alexey Eremin*

Institute of Experimental Physics, Otto von Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg E-mail: [email protected]

We report experimental studies of a transient flow in a collapsing freely suspended smectic liquid crystal film. In contrast to soap films, whose collapse has been studied in detail [1, 2], films of thermotropic liquid crystals have a well-defined layer structure and represent a quasi-two-dimensional fluid. The particular inner structure of smectics stabilizes freely suspended films with an extraordinary surface- to-volume-ratio of more than 106. Collapse dynamics have been extensively studied in smectic bubbles [3]. In our studies, we focus on the transient flow occurring in the accelerating region of the film near the propagating rim of a collapsing planar smectic film. We use tracer particles to visualise the flow, thus enabling us to test the predictions of the existing theory for collapse dynamics [4, 1]. Using high-speed imaging we show, that the advective flow involves the whole film, however, the flow velocity is gradually reduced with the distance from the moving edge. The dissipation region is nearly independent of the film thickness.

References [1] G. Taylor, Proc. Royal Soc. London A 1959, 253, 313–321. [2] A. B. Pandit and J. F. Davidson, J. Fluid Mech. 1990, 212, 11–24. [3] T. Trittel, T. John, K. Tsuji, and R. Stannarius, Phys. of Fluids 2013, 25, 052106. [4] F. E. C. Culick, J. Appl. Phys. 1960, 31, 1128–3.

Refractive and Diffractive Beam Splitters: Experiments and Simulations Atefeh Habibpourmoghadam, Markus Wahle, Alexander Lorenz* Department of Physical Chemistry, Paderborn University, 33098 Paderborn, Germany *[email protected]

We have successfully used a wedge cell (low wedge angle of 2.3°, filled with a nematic LC) as refractive beam splitter. Beam splitting of a focused laser beam could be achieved within the field of view of a 20x microscope objective lens (Fig. 1). Beam separation and intensity distribution of the generated beams were both varied smoothly by applying voltages of 1 to 3 V. Response times of a few seconds were observed and the responses were much faster, if a copolymer network LC was used.[1] However, in the latter case, on-off switching of the modulated beam was found instead of steering.

Fig. 1. Tuneable beam splitting of a focused laser beam observed with a 20x objective lens. A wedge- cell beam splitter (filled with E7) was used. The beams were observed with a CMOS camera fitted with a single linear polarizer (polarization direction indicated with double arrows).

Simulations were conducted to investigate the unexpected behaviour of the copolymer network LC. In our model, the Q-tensor approach was applied [2-4], where the dominant differential equations in the Q-tensor representation were the Euler- Lagrange equations, coupled with the Poisson equation to account for the applied electric-field distribution in the LC. To be able to consider all possible initial alignments of the LC, the governing equations were numerically calculated in three dimensions. By including rod like polymer beads in the simulations, we could show how the presence of polymer will decouple the local, field-induced LC realignment in-between neighbouring regions, which may well explain the field-responsive scattering losses in a wedge cell. In addition, we could show that polymer beads are highly useful to enhance the local optical phase contrast in devices with interdigitated electrodes and exploit their highly non-uniform field distributions much more effectively than would be possible in a neat LC, which is a huge step towards enhanced diffractive beam splitters.

Acknowledgements: Financial support by German Research Council grants LO 1922/4-1 and GRK 1464 is gratefully acknowledged.

References [1] A. Lorenz, L. Braun, V. Kolosova, ACS Photonics 2016, 3, 1188-1193. [2] H. Mori, E. C. Gartland, et al. Japanese Journal of Applied Physics 1999, 38, 135-146. [3] D. Donisi, R. Asquini, et al. Optics Express 2009, 17, 5251-5256. [4] R. James, E. Willman, et al. IEEE Transactions on electron devices 2006, 53, 1575-1582.

Nanosegregation and its Connection to “de Vries-like” Properties in Smectic Liquid Crystals

Carsten Müller1, Frank Giesselmann1*, Christopher P. J. Schubert2, Robert P. Lemieux2

1Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany 2Department of Chemistry, University of Waterloo, N2L 3G1 Waterloo, Ontario, Canada E-mail: [email protected]

In smectic A (SmA) to smectic C (SmC) transitions of the “de Vries”-type, the appearance of director tilt is coupled to a substantial increase in optical birefringence and thus in orientational order, the increase of which – more or less – compensates the smectic layer contraction in the SmC phase. [1] This mechanism however basically requires SmA phases with unusually low orientational order and rather high smectic order. A promising route towards “de Vries-like” smectics is thus the incorporation of nanosegregating segments such as terminal siloxane or carbosilane groups into the mesogens. [2] In these materials the direct isotropic to SmA transition is essentially driven by nanosegregation even though their orientational order remains low. We recently reported on a new chiral smectic liquid crystal QL32-6 undergoing a SmA* – SmC* transition with maximum layer contraction of only 0.2%. [3] We now investigated a series of similar mesogens (cf. Fig. 1a) all having a SmA* – SmC* phase sequence but with terminal carbosilane segments of different length to systematically study the influence of nanosegregation. The smectic layer spacings, the optical birefringence (Fig. 1b) and tilt angles as well as dielectric relaxation times and the rotational viscosities are studied and discussed with respect to the SmA* – SmC* phase transition and its “de Vries-like” character. All findings consistently show that the manifestation of “de Vries-like” behavior crucially depends on the nanosegregating subunit.

Figure 1. a) Chemical structures of the investigated smectic compounds and b) temperature dependent birefringence ∆n(T-TAC) of the three nanosegregating liquid crystals.

The authors gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG Gi 243/6-1) and the National Science and Engineering Council of Canada.

References [1] J. P. Lagerwall , F. Giesselmann, ChemPhysChem, 2006,7, 20–45. D. Nonnenmacher et al., ChemPhysChem, 2013, 14, 2990–2995. [2] J. C. Roberts et al., J. Am. Chem. Soc., 2008, 130, 13842–13843. C.P.J. Schubert et al., J. Mater. Chem. C, 2014, 2, 4581–4589. [3] C. P. J. Schubert et al., Chem. Commun. 2015, 63, 12601-12604. Estimation of DC Conductivity of Ferroelectric Liquid Crystals from Parameters of Low Frequency Dielectric Relaxation Modes

1,2) 2 2 1,2 Fedor Podgornov *, Maxim Gavrilyak , Nikolai Zaveivorota , Wolfgang Haase

1)Eduard Zintl Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Alarich Weissstr. D-64287, Darmstadt, Germany 2)Laboratory of Molecular Electronics, South Ural State University, Chelyabinsk, Lenin ave. 76, 454080, Chelyabinsk, Russia *E-mail: [email protected]

The measurements of DC conductivity (σDC) in a standard cell (consisting of glass substrates with sputtered ITO electrode and spin-coated with polymer alignment layers) is rather complicated problem. As a result, evaluation of σDC from the real part of conductivity spectra (as the horizontal asymptote at f →0) can be incorrect even at very low frequencies (f≈10-5 Hz). In this report we discuss the possibility to use both real (Fig.1a) and imaginary (Fig. 1b) parts of conductivity spectra for retrieving correct value σDC.. This approach is based on the utilization of the parameters of Maxwell-Wagner and electrode polarization modes obtained from the low frequency real (Fig.1a) and imaginary (Fig.1b) parts of the conductivity spectrum. By analyzing the equivalent electric circuit of a LC cell (Fig. 1c), the methods of the retrieving correct value of σDC will be presented.

a b

c

Figure1: log-log plots of real (a) and imaginary (b) parts of low-frequency conductivity spectra of FLC for different values of electric double layers capacitance. The simplified equivalent electric circuit of LC cell (c).

Strategies for Enhancing the Kerr effect in Polymer-Stabilized Blue Phase Liquid Crystals

a a a,b a Roman Rennerich , Bernhard Atorf* , Amanda Swanson and Heinz-Siegfried Kitzerow

[a] Department of Chemistry and Center of Optoelectronics and Photonics Paderborn, Paderborn University, Warburger Straße 100, 33098 Paderborn, Germany [b] Reed College, 3203 Southeast Woodstock Boulevard, 97202, Portland, Oregon, USA E-mail: [email protected] Blue phases (BPs) are liquid crystalline phases, which are optically isotropic due to their cubic superstructure of the local molecular alignment. The cubic structure is indicated by Bragg reflection (Fig. 1), if the lattice constant is similar to the wavelength of light. Blue phases appear in chiral liquid crystals or in mixtures of a nematic liquid crystal and a chiral dopant at temperatures between the cholesteric phase and the isotropic phase. In contrast to other isotropic liquids, they can show a very large electric field-induced birefringence (Kerr effect). Polymer-stabilized blue phases (PSBPs)[1] are produced through the UV-induced polymerisation of reactive monomers added to a BP mixture. The resulting polymer network stabilises the blue phase over a broad temperature range. Consequently, PSBPs are promising candidates for electro-optic applications. In our poster, we describe different attempts to reduce the switching voltage, namely changing the polymerisation temperature, decreasing the monomer concentration, changing the liquid crystal, changing the polymerisation wavelength or using a “template” method[2]. In the latter case, a PSBP is produced, then the liquid crystal mixture is removed from the sample (Fig. 2) and finally the sample is refilled with a liquid crystal mixture that contains a chiral dopant with opposite helical twisting power.

References

[1] H. Kikuchi, M. Yokota, Y. Hisakado, H. Yang, and T. Kajiyama, Nat. Mater. 2002, 1, 64–68. [2] H.-C. Jau, W.-M. Lai, et. al. Opt. Mater. Expr. 2013, 3, 1516-1522.

Observation of the Electro-Optic Kerr effect in the Isotropic Phase of Ionic Liquid Crystals

M. Christian Schlicka, Frank Giesselmann*a, Nadia Kapernauma, Manuel M. Neidhardtb, Sabine Laschatb

a Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany b Institute of Organic Chemistry, University of Stuttgart, 70569 Stuttgart, Germany E-mail: [email protected]

The Kerr effect is a quadratic electro-optic effect inherent to all states of matter and related to the molecular orientational order induced by an electric field E. The induced optical birefringence Δn increases with the electric field E as: Δn(λ,E) BλE 2 , where B denotes the temperature-dependent Kerr constant and λ the –11 -2 wavelength of light. For nematic liquid crystals such as 5CB (with B = 7.77·10 mV at T–TNI = 0.62 K) an exceptionally large Kerr effect was found in the pre-transitional regime from the isotropic to the nematic liquid crystalline phase. [1] Other examples of large Kerr effects were found in complex ionic fluids such as micellar solutions of ionic surfactants or polyelectrolyte solutions. [2,3]

In this contribution we present first detailed results of Kerr effect measurements in the isotropic phase of ionic liquid crystals (ILCs), namely the dependence of the Kerr effect on the temperature and the electric field strength. To avoid complications with ionic conductivity high frequency AC fields were applied and ILCs with low clearing temperatures were chosen. An example is seen in Fig. 1. In the case of ILCs the Kerr constants are found to be similar or even higher than the Kerr constant of 5CB. At high field strengths however we observe systematic deviations from Kerr’s law. Similarities and differences in the Kerr effect of ionic and non-ionic liquid crystals will be discussed.

Figure 1: a) Time resolved electro-optic Kerr response 0.6 K above the clearing temperature on application of a 1kHz square wave voltage; electrode gap: 20 µm. b) Molecular structure of the ILC.

Financial support by the Deutsche Forschungsgemeinschaft (DFG, Gi 243/8-1 and La 907/17-1) is gratefully acknowledged.

References [1] D. A. Dunmur, A. E. Tomes, Mol. Cryst. Liq. Cryst. 1981, 76, 231 [2] W. Oppermann, Makromol. Chem. 1988, 189, 927 [3] W. Schorr, H. Hoffmann, J. Phys. Chem.,1981, 85, 3160

Chiral Amplification in Hydrogen Bonded Liquid Crystals: Synthesis and Characterization

Taoufik Soltani*, Malek Fouzai, and Tahar Othman

Physics Laboratory of Soft Matter and Electromagnetic Modelling, Faculty of Sciences of Tunis, University of Tunis El Manar, El Manar. E-mail: [email protected]

Synthesis and application of fascinating liquid crystals earned a tremendous growth in the past few decades. However, the interplay between chirality and the liquid crystalline state is a subject of great interest from both the theoretical and the technological points of view. The central theme of the aimed research work involves the design, synthesis and characterization of two recent hydrogen bonded liquid crystals (4-oxyoctyl benzoic acid (8OBA) and 4-(octyloxy)-3-fluoro benzoic acid (8OBAF)) and a chiral agent (4(4’-octyloxybenzoyloxy)-bentzoate-S-1-methyl hepthyl). First, the formation of hydrogen bond is confirmed by FTIR spectroscopic and NMR studies. These homologs exhibit rich phase variance as evinced by various textures by polarizing optical microscopic (POM) and DSC studies. Phase diagram has been constructed through POM and DSC data. Second, the optical study of the two liquid crystals made it possible to determine the two ordinary and extraordinary refraction indices (no and ne) of the two compounds as well as their optical birefringences Δn. The liquid crystal nematic state of the two compounds was converted to the cholesteric state by doping with the chiral agent. The optical studies show that the chiral agent presents a remarkable solubility in the nematic liquid crystal hosts and a small helical twisting power HTP.

Computing Equilibrium Structures of Cholesteric Liquid Crystals in Elliptical Channels with a Deflation Algorithm

1 2 3 1 4 David B. Emerson , Scott MacLachlan , Patrick E. Farrell , James H. Adler and Timothy J. Atherton*

1Department of Mathematics, Tufts University, 503 Boston Ave., Medford, Massachusetts 02155, USA 2Department of Mathematics, Memorial University, St. John's, Newfoundland, Canada. 3Mathematical Institute, University of Oxford, Woodstock Road, Oxford OX2 6GG 4Department of Physics and Astronomy, Tufts University, 574 Boston Ave., Medford, Massachusetts 02155, USA E-mail: [email protected]

Cholesteric liquid crystals are complex fluids that exhibit long-range orientational order, elasticity, local alignment at surfaces, optical activity and response to external stimuli. They are composed of chiral molecules that, in the absence of boundaries adopt a helical structure with a preferred pitch q set by the molecular structure and the ambient temperature. There has recently been a great deal of interest in cholesterics in confined geometries because of parallels with other condensed matter systems such as chiral ferromagnets, Bose-Einstein condensates and the Quantum Hall effect. All of these systems exhibit topological defects including skyrmions and torons under confinement where the boundary conditions preclude adoption of the energetically preferred uniformly twisted state. Hence, they are geometrically frustrated. A key challenge in simulating these systems is that, due to the geometric frustration, they possess a particularly rich family of local minimizers of the free energy. The ground state strongly depends on the shape of the domain and material parameters, including the cholesteric pitch. Typically, minimization is performed from an initial guess using a relaxation algorithm, or by solving a set of nonlinear Euler- Lagrange equations. In either case, having found a solution, the question remains: are there others? It is also highly desirable to track the solution set as a function of geometric and material parameters to assemble a phase diagram. Here, we adapt a new technique known as the deflation method1 to a model problem in this class, the configuration of a cholesteric in an elliptical channel. The method is generalizable, robust, and computationally efficient for large-scale applications. We track the solution set as a function of aspect ratio and preferred pitch, and explore results for splay-bend liquid crystals.

Reference: [1] P. E. Farrell, A. Birkisson, and S. W. Funke, SIAM J. Sci. Comput. 2015 37, A2026 Nanosegregation in Smectic Liquid Crystals – A Coarse Grained MD Simulation Study

Christian Häge, Frank Giesselmann*, Frank Jenz, Stefan Jagiella

Institute of Physical Chemistry, University of Stuttgart, 70569 Stuttgart, Germany E-mail: [email protected]

Nanosegregation is of great importance for understanding smectic liquid crystal (LC) phases in particular in the case of the “de Vries” type smectics [1] or ionic liquid crystals. [2] In order to get a more detailed understanding of the impact of nanosegregation on smetic LC order, a series of molecular dynamics (MD) simulations were carried out. Following the general approach of Maiti et al. [3], the particle model used in the simulations consists of several Lennard-Jones (LJ) spheres that were “glued” together to form rigid particles of different shape. The two spheres in the middle of one particle have a potential which is more attractive than the potential of the outer spheres and thus a higher core-core interaction was obtained. In order to simulate nanosegregating units, the depth of the LJ potential ε was varied for the two LJ spheres in the center of the particle (see figure 1a) in different simulation runs. The orientational order parameter S, the 1D-translational order parameter Σ and the 2D X-ray diffraction patterns (see figure 2b) were calculated and evaluated for all simulations. In all cases the simulations lead to a direct phase transition from the isotropic phase to the smectic A phase, followed by a smectic C phase. Obviously, the enhanced core-core interactions make nanosegregation the driving force for the LC formation and thus no nematic phase is observed. A systematic investigation of the influence of the depth of the LJ potential ε of the core particles has been made and a phase diagram will be presented.

a) b)

Figure 1: a) Schematic model used in the simulations. Different angles ψ (from 0 ° to 90 °) were used and the depth of the LJ potential ε of the grey spheres was varied in order to simulate nanosegregation. b) A 2D diffraction pattern calculated from a smectic A phase simulation. [4]

References

[1] C. P. J. Schubert, C. Müller, F. Giesselmann, R. P. Lemieux, J. Mater. Chem. C 2016, 4, 8483– 8489. [2] K. Goossens, K. Lava, C. W. Bielawski, K. Binnemans, Chem. Rev. 2016, 116, 4643–4807. [3] P. K. Maiti, Y. Lansac, M. A. Glaser, N. A. Clark, Phys. Rev. Lett. 2004, 92, 025501. [4] F. Jenz, S. Jagiella, M. A. Glaser, F. Giesselmann, ChemPhysChem 2016, 17, 1568–1572. Systematic Coarse-Graining for Nonequilibrium Dynamics of Liquid Crystals

Anoop Varghese*, Patrick Ilg

Department of Mathematics and Statistics, University of Reading, RG6 6AX, Reading, UK E-mail: [email protected]

Nonequilibrium relaxation of liquid crystals is studied using a systematic coarse-graining procedure based on projection operator formalism. In particular, the relaxation dynamics of the order parameter tensor from nonequilibrium states is considered. The coarse-graining procedure employs a miscroscopic Hamiltonian as the starting point and yields a closed form transport equation for the order parameter tensor. The equation is given in terms of friction coeffients and gradient of generalised Landau-de-Gennes free energy of the microscopic system. The friction coefficients are determined by the microscopic fluctuations and are readily obtained from molecular dynamics simulations. The extended Landau-de-Gennes free energy can be obtained using Monte Carlo simulations. The procedure is illustrated using Lebwohl-Lasher and Gay-Berne models of liquid crystals. We demonstrate that the dynamics of the systems relaxing back to equilibrium is well described by the coarse-grained transport equations. The applicability of the coarse-graining method for studying the rheology of liquid crystals under flow conditions is also briefly discussed.

References [1] H. Stark, T. C. Lubensky, Physical Review E 2002, 67, 0601709 [2] P. Ilg, Physical Review E 2012, 85, 061709 [3] A. M. Luo, L. M. Sagis, H. C. Öttinger, C. De Michel, P. Ilg, Soft Matter 2015, 11, 4383 [4] P. Ilg, Journal of Non-equilibrium Thermodynamics 2016, 41, 89 [5] H. C. Öttinger, Beyond Equilibrium Thermodynamics 2005, John Wiley & Sons Molecular Dynamics Simulation of a Smectic-A: Do the Viscosities Diverge?

Junju Mua , Andrew Mastersa,*, Michael P. Allenb,c

aSchool of Chemical Engineering & Analytical Science, University of Manchester, Manchester M13 9PL, UK. bH. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK cDepartment of Physics, University of Warwick, Coventry CV4 7AL, UK *E-mail: [email protected]

We present molecular dynamics results on the transport coefficients of a smectic-A liquid crystal. These properties are of particular interest due to theoretical claims that four of the five smectic-A viscosities are divergent at zero frequency, diverging as the inverse of the frequency [1]. This divergence is predicted to occur via the coupling of elements of the stress tensor to layer fluctuations. There is some limited experimental evidence in support of this divergence, but it is of insufficient sensitivity to quantitatively test theory [2–5]. Computer simulations can hopefully cast further light on this phenomenon. We study a system of 9000 Gay–Berne particles. Details of the model are given in [6]. Our simulations reveal anomalous single particle rotational diffusion, similar to that previously observed in a nematic [6], but our main result is that the stress–stress autocorrelation functions appear to show no significant long time behaviour. This translates into normal, non-diverging viscosities at zero frequency, at odds with theoretical predictions. We will present possible reasons for this discrepancy.

Figure 1: Snapshot of the Smectic-A system.

References

[1] G. Mazenko, S. Ramaswamy, & J. Toner, Physical Review Letters 1982, 49(1), 51–53. [2] S. Bhattacharya, S. Shen, & J. Ketterson, Physical Review A 1979, 19(3), 1219. [3] S. Bhattacharya, B. Cheng, B. Sarma, & J. Ketterson, Physical Review Letters 1982, 49(14), 1012–1015. [4] V. Balandin, S. Pasechnik, V. Prokopjev, & O. Shmelyoff, Liquid Crystals 1988, 3(10), 1319–1325. [5] D. Bogdanov, E. Gevorkyan, & Y. Obydenkov, Technical Physics Letters 2012, 38(2), 138–139. [6] Humpert, A. J. Masters, & M. P. Allen, The European Physical Journal Special Topics 2016, 225(8–9), 1723–1732.
H-,

INTEGRATION OF POLYMER FILMS IN CARBON NANOTUBE COATED SUBSTRATES FOR LC CELLS

Hakam Agha, MD Asiqur Rahman, K. Truong, J. H. Park, D. Suh, G. Scalia*

1. Physics and Material Science Unit, University of Luxembourg, 162a, Avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg 2. Department of Energy Science, Sungkyunkwan University, 440-746, Suwon, Korea E-mail: [email protected]

Carbon nanotube (CNT) sheets formed by aligned networks of tubes pulled from forests are attractive technological components thanks to the relative enhancement of the macroscopic properties such as electrical conductivity along the pulling direction [1][2]. These aligned CNT sheets can be used as transparent electrodes due to their high conductive properties and optical transparency. Furthermore, their compatibility with flexible substrates, combined with excellent mechanical characteristics, makes them attractive candidate for flexible electronics. Similar to graphitic surfaces, CNT sheets also have anchoring effect on liquid crystal (LC) molecules inducing planar alignment [3]. The aligned geometry with nanoscale dimensions of the CNT sheets acts as unidirectional alignment template for the LC [4][5]. Therefore, even bare CNT layers can be envisaged for use in LC electro-optic devices. However, this templating action on LC has been only very little explored so far and aspects regarding the anchoring or the effect on the azimuthal angular distribution is still not known. Also, several practical issues need to be addressed not only for applying these layers but also for performing measurements for investigating the properties. In the present work, we describe our efforts in incorporating a thin polymer film with high optical transparency below the surface of the CNT sheets. This step is necessary to insure an insulating layer between the electrodes and CNT sheets and prohibit any undesired short circuits. The films are obtained by means of spin- coating, and their thickness and morphology is characterized by atomic force microscopy (AFM). In addition, we report the observations of the adhesion behaviour of CNTs on the surface of films realized with different types of polymers. Particular attention is devoted to the electrical characteristics of the multilayer structure, i.e. electrodes, polymer and CNT sheet layers, for a successful and safe employment in LC cells.

References: [1] M. Zhang, S. Fang, A. A. Zakhidov, S. B. Lee, A. E. Aliev, C. D. Williams, Ken R. Atkinson, Ray H. Baughman, Science, 2005, 309 (5738), 1215-1219. [2] T. K. Truong, Y. Lee, and D. Suh, Curr. Appl. Phys., 2016, 16 (9), 1250–1258. [3] G. Scalia, J. P. F. Lagerwall, M. Haluska, U. Dettlaff-Weglikowska, F. Giesselmann, S. Roth, Phys. Status Solidi B, 2006, 243, (13), 3238-3241. [4] J. M. Russell S. Oh, I. LaRue, O. Zhou, E. T. Samulski, Thin Solid Films, 2006, 509, 53-57. [5] W. Fu, L. Liu, K. Jiang, Q. Li, S. Fan, Carbon, 2010, 48, 1876-1879.

page 100e Participants

Dr. Acreman Andrew Sharp Laboratories of Europe Dr. Agha Hakam University of Luxembourg H-, Dr. Akpinar Erol Abant Izzet Baysal University Dr. Atherton Tomothy Tufts University P50 Mr. Atorf Bernhard University of Paderborn O29 Mrs. Bader Korinna University of Stuttgart P21 Mrs. Bahndorf Katrin University of Würzburg P22 Prof. Dr. Brand Helmut R. University of Bayreuth O19 Mr. Braun Lukas University of Mainz Prof. Dr. Bremer Matthias Merck KGaA I6 Mrs. Bühlmeyer Andrea University of Stuttgart P31 Dr. Chakrabarti Buddhapriya University of Sheffield O27 Mr. Chemingui Marouen University of Tunis El Manar Prof. Dr. Cleaver Doug Sheffield Hallam University O8 Dr. Dähmlow Patricia University of Magdeburg O24 Mr. Dechant Moritz University of Würzburg P29, PA12 Hjg^&

page 10) 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Participants

Mr. Klopp Christoph University of Magdeburg O25 Mrs. Knecht Frederike University of Stuttgart P18 Prof. Dr. Lagerwall Jan University of Luxembourg P42 Mr. Lakey Christopher University of Warwick P19 Mr. Lambov Martin University of Würzburg P20, PA6 Prof. Dr. Laschat Sabine University of Stuttgart Prof. Dr. Lehmann Matthias University of Würzburg Mr. Limbach Daniel University of Mainz P27 Dr. Lorenz Alexander University of Paderborn O20 Dr. Lydon John University of Leeds I3 Miss Macaskill A. Helen University of Leeds O16 Mr. Mackay Fraser University of Edinburgh O26 Mr. Maier Philip University of Würzburg P32 Mr. Maisch Stefan University of Würzburg P12, PA4 Dr. Mandle Richard University of York P11, P13, I2 Prof. Dr. Masters Andrew University of Manchester O7 Prof. Dr. Mehl Georg University of Hull Mr. Miller Lukas University of Würzburg Mr. Mistry Devesh University of Leeds O18 Prof. Dr. Mottram Nigel University of Strathclyde I4 Mr. Mu Junju University of Manchester P53 Mr. Mulcahy Stephan Merck Chemicals Ltd. Mr. Müller Carsten University of Stuttgart P45 Dr. Nordendorf Gaby University of Cambridge Mrs. Normand Margaret University of Edinburgh P38, PA3 Mrs. Oehlhof Annette University of Mainz Mr. Ohnemus Michael University of Würzburg Mr. Osipov Mikhail University of Strathclyde P7, O10 Mr. Pankaj Kumar Tripathi Banaras Hindu University P3 Mr. Pfletscher Michael University of Duisburg-Essen P23 Dr. Podgornov Fedor South Ural State University P1, P46, O2 Mr. Poppe Marco University of Halle-Wittenberg O13 Mr. Poppe Silvio University of Halle-Wittenberg P34 Mr. Potisk Tilen University of Bayreuth O1 Mr. Rahman MD Asiqur University of Luxembourg P5 Mr. Rennerich Roman University of Paderborn P47 Mr. Reppe Tino University of Halle-Wittenberg P33 Mrs. Reshetnyak Oksana University of Kyiv Prof. Dr. Reshetnyak Viktor University of Kyiv I5 Dr. Rieth Thorsten University of Mainz Mrs. Roth Sabine University of Würzburg P35 Dr. Scalia Giusy University of Luxembourg P6 Mr. Schlick Christian University of Stuttgart P48 Dr. Schmidke Jürgen University of Paderborn O28 Dr. Snow Benjamin Merck Chemicals Ltd. Dr. Soltani Taoufik University of El Manar P49 Mr. Spengler Matthias University of Duisburg-Essen P24 Mr. Srigengan Shajeth University of Leeds P9 Prof. Dr. Stannarius Ralf University of Magdeburg Mrs. Tober Natalie University of Mainz P26 Mrs. Trbojevic Nina University of Leeds P8

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 10* Participants

Prof. Dr. Tschierske Carsten University of Halle-Wittenberg Prof. Dr. Ungar Goran University of Sheffield O17 Dr. Vanhoyland Geert Bruker AXS GmbH Dr. Varghese Anoop University of Reading P52 Dr. Vollbrecht Joachim University of Paderborn P37, PA9 Mr. von Rüling Florian University of Magdeburg P43, PA8 Mr. Wahle Markus University of Paderborn O22 Mr. Walton Josh University of Strathclyde P10, PA7 Prof. Dr. Weissflog Wolfgang University of Halle-Wittenberg Dr. Welch Chris University of Hull O4 Dr. Wetzel Christoph Merck KGaA Dr. Wilkes David Merck KGaA Prof. Dr. Wilson Markus University of Durham P14 Mrs. Wurzbach Iris University of Stuttgart O30 Mr. Wyatt Peter University of Leeds Dr. Zeng Xiangbing University of Sheffield O5 Mrs. Zhang Bingru University of Paderborn P15

page 10+ 2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 Map with Restaurants

2nd Joint German-British Liquid Crystal Conference, Würzburg April 3-5, 2017 page 10, Institut für Organische Chemie Am Hubland 97074 Würzburg