The British Liquid Crystal Society Conference 2015

BLCS 2015

Sheffield Hallam University

Monday 30th March to Wednesday 1st April 2015

Sponsors

The British Liquid Crystal Society and Sheffield Hallam University are very grateful to the sponsors, who have helped make this conference possible. Please take a moment to look through the services our sponsors can provide for you.

Merck KGaA Frankfurter Straße 250 64293 Darmstadt Germany Tel.: +49 (0) 6151 72-0 Fax: +49 (0) 615172-2000

Taylor & Francis Customer Services Bookpoint 130 Milton Park Abingdon Oxon OX14 4SB UK Tel: +44 (0) 1235 400 524 Fax: +44 (0) 1235 400 525 Email (UK Trade): [email protected]

Kingston Chemicals Limited Department of Chemistry University of Hull Hull HU6 7RX UK. Tel: +44(0)1482465866 Fax: +44(0)1482466410 www.hull.ac.uk/kingston-chemicals/

Welcome

Dear Delegate

Welcome to Sheffield Hallam University, hosts of the 29th Annual British Liquid Crystal Society Conference. The programme contains a broad mix of science and engineering, with a large number of contributing institutions and, as per tradition, a high proportion of student presentations - we are sure that there is something for everyone.

As detailed below, all conference presentations and lunches will be in the Cantor Building of SHU's city campus, which is an easy walk from Sheffield Station. The conference hotel, the Jurys Inn is less than a hundred metres from Cantor. Evening meals will be in the Hallam View restaurant in SHU's main building. These locations, plus other places of interest (The Red Lion, The Millennium Gallery, …) are all marked on the map on the next page.

We would like to thank all of the contributing presenters, both talks and posters, for providing such an interesting and varied set of Abstracts sharing their research and stimulating interesting discussions.

We hope you enjoy the event.

Key Information

Conference Organisation The local Conference Organiser is Doug Cleaver, MERI, Sheffield Hallam University. If you require assistance at any point, please contact him on [email protected]. Alternatively you can speak to Tim Spencer, Alireza Dastan or Fatima Chami (a SHU graduate) who comprise the rest of the home team.

Registration The registration desk will be located by the entrance foyer of the CANTOR BUILDING on Arundel Street. Poster boards and velcro will be available in the ground-floor Atrium space. Additionally, a luggage room will be available for safe storage on Monday 30th and Wednesday 1st please ask at the registration desk if you wish to make use this room.

Lectures These will all be held in the Cantor Building lecture theatre, room 9130 located on the first floor. Smaller rooms on the first floor of the Cantor building will be used for other gatherings. There is a permanent lectern set- up in 9130 with a Windows 7 PC containing full Microsoft Office, Adobe software and internet access. Please ensure that your presentations are uploaded at the very latest during the break before your presentation. Presentations may be downloaded or uploaded via external drives. Alternatively, personal laptops can be used for presentations, but it is your responsibility to ensure both power and video adapters are available. A standard PC serial cable is provided.

Talks range in: 50 minutes Plenary 30 minutes Invited 20 minutes Contributed

Please allow a few minutes of your allocated time for questions.

Posters These are located in the ground floor Atrium of the Cantor Building, just to the left of the registration table. The Taylor and Francis stand will also be in this area. Poster boards are 1810 x 923mm. These will just fit an A0 in portrait orientation and comfortably hold A1 in portrait or landscape orientation. The poster boards are numbered - please check the programme to identify your number. The poster boards are brand new, so please use the velcro provided!

Accomodation The Jurys Inn hotel is less than 100 metres from the Cantor Building. It has its own underground car-park, which can be booked separately. Jurys Inn, 119 Eyre Street, Sheffield, S1 4QW

Day-parking If you require day-parking, we recommend you use the APCOA car park on Arundel Gate (opposite the Jurys Inn). This is also known at the Kit-Kat building (you'll understand why when you see it). If you "beep" you blue car- park token at the Cantor reception desk, then this just costs £3 per day. Leaving your car overnight will incur higher charges though.

Lunches and Drinks Breaks All lunches and drinks breaks will be held in the ground floor Atrium of the Cantor Building.

Evening Meals Both Evening meals will be held in Hallam View Restaurant located in the Owen Building on the university campus map. This is a 5 minute walk away from the Jurys Inn hotel and 3 minute walk from the Cantor Building conference venue - unless you stop off at the Red Lion en-route. Juice will be provided on the Monday evening. Juice and wine will be provided on the Tuesday evening.

WIFI Eduroam is available throughout the SHU Campus. Alternatively, individual logins to the SHU-GUEST Wi-Fi server can be obtained from the Registration Desk or the Conference Organisers.

Sheffield Hallam University Campus Map & Getting About

Some upcoming LC dates for the diary

Event: SID Display Week 2015 When: Sunday, May 31- June 5, 2015 Location: San Jose, CA, USA Link: http://www.displayweek.org/

Event: Chirality at the Nanoscale workshop When: Thursday, Jun 4-5, 2015 Location: The Nanoscale workshop, LCI, Kent State University (OH), USA Link: http://www.lcinet.kent.edu/conference/25/index.php

Event: Gordon conference on liquid crystals: Liquid Crystallinity in Soft Matter at and Beyond Equilibrium When: Sunday, Jun 21-26, 2015 Location: University of New England, 11 Hills Beach Rd, Biddeford, ME 04005, United States Link: http://www.grc.org/programs.aspx?id=11481

Event: 15th International Conference on Ferroelectric Liquid Crystals: Challenges in polar self-assembling systems When: Sunday, Jun 28-July 3, 2015 Location: Prague, Czech Republic Link: http://palata.fzu.cz/flc15/

Event: IMID 2015 When: Tuesday, Aug 18-21, 2015 Location: Daegu, South Korea Link: http://www.imid.or.kr/

Event: European Conference on Liquid Crystals (ECLC) 2015 When: Saturday, Sep 7-11, 2015 Location: Manchester, UK Link: https://www.meeting.co.uk/confercare/eclc2015/

Event: 8th International Liquid Crystal Elastomer Conference (ILCEC15) When: Friday, Oct 2-7, 2015 Location: Erice, Italy Link: http://people.sissa.it/~desimone/iWeb/ILCEC15/Welcome.html

Event: The 22nd International Display Workshops When: Wednesday, Dec 9-11, 2015 Location: Otsu, Japan Link: http://www.idw.or.jp/

Event: Pacifichem 2015 with Symposium #447 on Self-Organization: Novel Mesogens and Applications When: Tuesday, Dec 15, 2015 Location: Honolulu, HI, USA !! Link: http://www.pacifichem.org/

Event: 30th BLCS Meeting When: Monday, Mar 21-23, 2016 Location: UK Link: http://blcs.eng.cam.ac.uk/

Programme for BLCS 2015

DAY ONE - Monday 30th March

Time Location Event Title Speaker 10:30 Cantor Entrance Registration 12:00 Cantor Atrium Lunch & Poster put-up / BLCS Committee Meeting Cantor 9137 Session 1 - Liquid Crystal Nanoparticle Systems - Chair Doug Cleaver 13:00 Cantor 9130 Welcome / Opening Doug Cleaver 13:05 Cantor 9130 Plenary 1 Liquid-Crystal-Directed Nano-Assemblies Linda Hirst 13:55 Cantor 9130 Talk 1 Colloids in Blue Phase Liquid Crystals Anne Pawsey Computer simulations of an anionic chromic dye: spontaneous symmetry breaking to form 14:15 Cantor 9130 Talk 2 Romnik Thind chiral aggregates and the formation of a novel smectic phase 14:35 Cantor Atrium Drinks Session 2 - Competing Components And Environments - Chair Ingo Dierking 14:55 Cantor 9130 Invited 1 What does a Liquid Crystal Do in a Gyroid? Tim Atherton Design and investigation of a gold nanoparticle 15:25 Cantor 9130 Talk 3 side-chain liquid crystal polymer Olusegun Amos nanocomposite A combined experimental and computational 15:45 Cantor 9130 Talk 4 study of anthraquinone dyes as guests within Mark Sims nematic liquid crystal hosts Multiscale models of metallic inclusions in Thomas Paul 16:05 Cantor 9130 Talk 5 nematic liquid crystals Bennett Further tricritical and antinematic behaviour in a 16:25 Cantor 9130 Talk 6 Fulvio Bisi revisited mildly repulsive Straley model 16:45 Cantor 9130 BLCS AGM 2015 Session 3 - Split Session Dr Simon Crook, Cantor 9131 "On the future of liquid crystals and optics" discussion Senior Manager 17:00 (parallel) EPSRC Cantor Atrium Poster Session 1 18:00 Check-in at Jurys Inn Hotel (Arundel Gate) & Drinks Red Lion (Charles Street) 19:00 Hallam View Evening Meal

Programme for BLCS 2015

DAY TWO - Tuesday 31st March

Time Location Event Title Speaker Session 4 - Lyotropics - Chair Helen Gleeson 2015 Sturgeon Lecture: 9:00 Cantor 9130 Plenary 2 Structure and Lyotropic Liquid-Crystalline John Seddon Phase Behaviour of Lipid Membranes Origin of Chirality in the Triple Network Tri- 9:50 Cantor 9130 Talk 7 continuous Cubic Phase Formed by Achiral Xiangbing Zeng Rod-like Molecules Coarse Grained Modelling of the Phase 10:10 Cantor 9130 Talk 8 Behaviour of Non-Ionic Surfactants with the George Jackson SAFT-g force field 10:30 Cantor Atrium Drinks Session 5 - Bent Cores AND Dimereric Mesogens - Chair Andrew Masters BLCS Young Scientist Award Lecture: Understanding unusual electric field-driven 10:50 Cantor 9130 Plenary 3 Mamatha Nagaraj reorganisations in the mesophases of bent-core liquid crystals Synthesis and properties of asymmetric dimeric materials with lateral and terminal fluorine 11:40 Cantor 9130 Talk 9 Dave Allan substituents for dual frequency liquid crystal mixtures Liquid crystal dimers: A molecular level and 12:00 Cantor 9130 Talk 10 Martin Walker mesoscale study Raman scattering studies of orientational order parameters in liquid crystalline dimers 12:20 Cantor 9130 Talk 11 Vitaly Panov exhibiting conventional and twist-bend nematic phases 12:40 Cantor Atrium Lunch / BLCS Committee Meeting Cantor 9137 Session 6 - Gray Medalists - Chair Peter Raynes 13:40 Cantor 9130 Plenary 4 From Biaxiality to Bistability and Back Again Cliff Jones 14:30 Cantor 9130 Plenary 5 Solid Liquid Crystals Mark Warner 15:20 Cantor Atrium Drinks Session 7 - Liquid Crystal Dynamics - Chair Tim Spencer Complex Rheology of Nematogenic Fluid; Buddhapriya 15:40 Cantor 9130 Talk 12 Connection to Elastic Turbulence Chakrabarti Interfacial motion by mean curvature in liquid 16:00 Cantor 9130 Talk 13 Amy Spicer crystals A computationally efficient Q-tensor model with Yogesh Kumar 16:20 Cantor 9130 Talk 14 flow for nematic liquid crystals Murugesan Rheology of Cholesteric Liquid Crystalline 16:40 Cantor 9130 Talk 15 Oliver Henrich Phases Session 8 - The Posters 17:00 Cantor Atrium Posters - with juice, beer and wine served from 17:30 onwards 18:30 Freshen up / Red Lion tipple 19:00 Hallam View Conference Dinner

Programme for BLCS 2015

DAY THREE - Wednesday 1st April

Time Location Event Title Speaker Session 9 - Application And Applications I - Chair Verena Gortz Anisotropic Dielectrophoresis – Nematic Liquid 9:00 Cantor 9130 Talk 16 Antariksh Saxena Crystals 9:20 Cantor 9130 Talk 17 Bleaching wave dynamics in photobending Chen Xuan Graphene based electrodes for electrically 9:40 Cantor 9130 Talk 18 Sarabjot Kaur, switchable liquid crystal contact lenses The investigation of mixtures of functionalized 10:00 Cantor 9130 Talk 19 azocines – can LC phase behaviour be James Hussey promoted by irradiation? 10:20 Cantor Atrium Drinks Session 10 - Application and Applications II - Chair Carl Brown Improving the optical performance of liquid 10:40 Cantor 9130 Talk 20 crystal contact lenses by implementing axial James Bailey alignment Acousto-optics in dispersed LC systems for Oksana 11:00 Cantor 9130 Talk 21 applications in ultrasonics Trushkevcyh Myelin: 19th Century Microscopy, Giant Squid 11:20 Cantor 9130 Invited 2 John Lydon (and a Duel with Bismarck) 11:50 Cantor 9130 Prizes and Closing 12:00 Cantor Atrium Lunch, poster take-down and farewells.

Plenary & Invited Talks

BLCS 2015 Talks Presenting Other Authors Affiliations Author Plenary Speakers (50 mins) PI 1 Liquid-Crystal-Directed Linda Hirst - University of Nano-Assemblies California, Merced, USA PI 2 Structure and Lyotropic J.M. Seddon - Imperial College Liquid-Crystalline London Phase Behaviour of Lipid Membranes PI 3 Understanding unusual M. Nagaraj - University of electric field-driven Manchester reorganisations in the mesophases of bent-core liquid crystals PI 4 From biaxiality to J. Cliff Jones - University of bistability, and back again Leeds PI 5 Solid Liquid Crystals Mark Warner - University of Cambridge Invited Speakers (30 mins) I 1 What does a Liquid Crystal Tim J Atherton - Tufts Do in a Gyroid? University, Medford, MA, USA I 2 Myelin: 19th century John Lydon - The University, microscopy, giant squid Leeds (and a duel with Bismarck).

Contributed Talks

BLCS 2015 Talks Presenting Other Authors Affiliation Author (presenter) Regular Speakers (20 mins) T 1 Colloids in Blue Phase Anne Pawsey Paul. S. Clegg University of Liquid Crystals Edinburgh T 2 Computer simulations of Romnik Thind Mark R. Wilson Durham an anionic chromic dye: University spontaneous symmetry breaking to form chiral aggregates and the formation of a novel smectic phase T 3 Design and investigation of Olusegun Amos G. H. Mehl University of a gold nanoparticle side- Hull, chain liquid crystal polymer nanocomposite T 4 A combined experimental Mark Sims L. C. Abbott, S. J. The and computational study of Cowling, J. W. University of anthraquinone dyes as Goodby, and J. N. York guests within nematic Moore liquid crystal hosts T 5 Multiscale models of Thomas Paul G. D’Alessandro, University of metallic inclusions in Bennett K.R. Daly Southampton nematic liquid crystals T 6 Further tricritical and Fulvio Bisi G. De Matteis and Università di antinematic behaviour in a S. Romano Pavia, Italy revisited mildly repulsive Straley model T 7 Origin of Chirality in the Xiangbing Zeng G. Ungar, F. Liu, University of Triple Network Tri- C. Dressel, M. Sheffield continuous Cubic Phase Prehm and C. Formed by Achiral Rod- Tschierske like Molecules T 8 Coarse Grained Modelling George Jackson O. Lobanova, C. Imperial of the Phase Behaviour of Herdes and E. A. College Non-Ionic Surfactants with Müller London the SAFT-g force field T 9 Synthesis and properties of Dave Allan M. Hird University of asymmetric dimeric Hull materials with lateral and terminal fluorine substituents for dual frequency liquid crystal mixtures T 10 Liquid crystal dimers: A Martin Walker Mark Wilson Durham molecular level and University mesoscale study

T 11 Raman scattering studies of Vitaly Panov Zhaopeng Zhang, University of orientational order Mamatha Nagaraj, Manchester parameters in liquid Richard J. Mandle, crystalline dimers John W. Goodby, exhibiting conventional Geoffrey R. and twist-bend nematic Luckhurst, J. Cliff phases Jones and Helen F. Gleeson T 12 Complex Rheology of Buddhapriya R. Mandal, D. Durham Nematogenic Fluid; Chakrabarti Chakraborty, and University Connection to Elastic C. Dasgupta Turbulence T 13 Interfacial motion by mean Amy Spicer Apala Majumdar University of curvature in liquid crystals Bath T 14 A computationally efficient Yogesh Kumar D’Alessandro G University of Q-tensor model with flow Murugesan and De Matteis G Southampton for nematic liquid crystals T 15 Rheology of Cholesteric Oliver Henrich K. Stratford, M.E. University of Liquid Crystalline Phases Cates and D. Edinburgh Marenduzzo T 16 Anisotropic Antariksh C. Tsakonas, I.C. Nottingham Dielectrophoresis – Saxena Sage, G. McKay, Trent Nematic Liquid Crystals N.J. Mottram, R.P. University Tuffin and C.V. Brown T 17 Bleaching wave dynamics Chen Xuan Mark Warner University of in photobending Cambridge T 18 Graphene based electrodes Sarabjot Kaur D. Mistry, H. University of for electrically switchable Milton, I. M. Syed, Manchester liquid crystal contact lenses J. Bailey, Y. J. Kim, K. S. Novoselov, C. J. Jones, P. B. Morgan and H. F. Gleeson T 19 The investigation of James Hussey G. H. Mehl University of mixtures of functionalized Hull azocines – can LC phase behaviour be promoted by irradiation? T 20 Improving the optical James Bailey S. Kaur, D. Mistry, University of performance of liquid H. F. Gleeson and Leeds crystal contact lenses by J.C. Jones implementing axial alignment T 21 Acousto-optics in Oksana Tobias J. R. University of dispersed LC systems for Trushkevcyh Eriksson, Silvaram Warwick applications in ultrasonics N. Ramadas and Rachel S. Edwards

Posters

BLCS 2015 Posters Presenting Other Authors Affiliations Author P 1 Turbulent Textures - Art Ingo Dierking - University of with Liquid Crystals Manchester P 2 Using DPD Simulation to Sarah Gray Mark R. Wilson Durham Study Phase Behaviour of University Liquid Crystal-Gold Nanoparticle Composite Materials P 3 All Optical Switching of Linda S Hirst - University of Nematic Liquid Crystal California, Films Driven by Localized Merced, USA Surface Plasmons P 4 High-Speed Microscope T. J. Atherton C. Burke, D. Tufts Imaging of Liquid Crystal Emerson, Y. Jin, J. University, Dynamics Guasto and J. H. MA, USA Adler P 5 Synthesis and Properties of Rami Pasha Michael Hird University of Novel Liquid Crystals with Hull Bulky Terminal Groups Designed for Bookshelf Geometry Ferroelectric Mixtures P 6 Homeotropic alignment in D. Mistry I. M. Syed, S. University of switchable optical power, Kaur, H. Milton, Manchester liquid crystal contact lenses J.Bailey, J.C. Jones, P. B. Morgan, J. H. Clamp and H. F. Gleeson P 7 The dynamic response of Marianna Cliff Jones and University of nematic devices with an Minarova and Helen F. Gleeson Manchester unconventional geometry Shajeth Srigengen P 8 Measuring the temperature David L. Wei Mark R. University of dependence of the Dickinson, James Manchester anisotropic viscosity of Bailey, Cliff Jones nematic liquid crystals and Helen F. using laser tweezer Gleeson techniques P 9 Molecular Dynamics Alireza Dastan Doug Cleaver Sheffield Simulation of Fibre Hallam Formation University P 10 Polarized Raman Zhaopeng Helen F Gleeson University of Spectroscopy Zhang Manchester Measurements of Liquid Crystal Order Parameters

P 11 Novel Resists for Karolis Farhan Hasan, University of Nanofabrication on Virzbickas Greg O’Callaghan, Birmingham Insulating Substrates Dennis Zhao, Jon A. Preece and Alex P. G. Robinson P 12 Structure and organisation F. Chami M.R. Wilson Durham in chromonic phases: MD University simulation study of Azo dyes in aqueous solution P 13 AFM study of R. B. Zhang X. B. Zeng, V. University of supermolecular dendritic Percec and G. Sheffield liquid quasicrystals Ungar P 14 Hexagonal Close Pack M. H. Yen J. Chaiprapa, X. University of Structures in Thermotropic Zeng, L Cseh, G. Sheffield Liquid Crystals H. Mehl, and G. Ungar P 15 Chessboard and Wigwam Huanjun Lu Feng Liu, University of phases in X-Shaped Xiangbing Zeng, Sheffield Polyphiles Goran Ungar, Hergold Ebert and Carsten Tschierske P 16 Novel mesomorphic Craig T. Richard J. Mandle, The behaviour of a chirally- Archbold Edward J. Davis, University of doped liquid crystal dimer, Stephen J. York exhibiting the twist-bend Cowling and John nematic phase W. Goodby P 17 Investigation of the J. W. Foster and V. P. Panov, M. University of Electric Field-Induced J. Ish-Horowicz Nagaraj and J.C. Manchester Behaviour of Biaxial, Jones Smectic Liquid Crystals using a Phase Sensitive Detection Method P 18 UV stability of liquid Philip J.W. Shuyu Yang and University of crystal lasers during Hands Michael P. Shaver Edinburgh polymer stabilisation P 19 The investigation of E. Ramou Z. Ahmed, C. University of mixtures of dimers forming Welch and G. H. Hull a N and a Nx/tb phase Mehl P 20 Liquid Crystal Infiltrated J.A. Dolan T.J. Atherton, J.J. University of Gyroid Optical Baumberg, U. Cambridge, Metamaterials Steiner and T.D. Wilkinson P 21 Developing Conductive Dennis Zhao Greg O’Callaghan, University of Organic Molecular Resists Owen Jones, Birmingham for Nanofabrication of Farhan Hasan, Insulating Materials Karolis Virzbickas, Jon A. Preece and Alex P. G. Robinson

P 22 Polarization-independent M. Nagar and H. H. Milton, S. Kaur, University of switchable liquid crystal F. Gleeson J. C. Jones and P. Manchester lenses based on the B. Morgan dark conglomerate phase P 23 Colloid – Liquid Crystal T. A. Wood J. S. Lintuvuori, A. University of Gels B. Schofield, D. Edinburgh Marenduzzo and W. C. K. Poon P 24 The effect of a methylene Jordan P John MD Storey University of link in the flexible spacer Abberley and Corrie T imrie Aberdeen of liquid crystal dimers P 25 Application of EPR Christopher Vasily S. University of Spectroscopy and Prior Oganesyan East Anglia Molecular Dynamics Simulations to a Lyotropic Liquid Crystal – A Combined Approach P 26 Conductive Resists for F. Hasan G. O'Callaghan, University of Nanofabrication on J.A. Preece and Birmingham Insulating Substrates A.P.G. Robinson P 27 Numerical Modelling of Menyang Yang Prashant Patel, F. University Cholesteric Droplets Anibal Fernandez College and Sally Day London P 28 A c2mm Liquid Crystal Warren Ziauddin Ahmed, University of Phase Formed by Dimer Stevenson Xiangbing Zeng, Sheffield, Molecules Goran Ungar and Georg Mehl P 29 An isothermal nematic to Daniel A. A. Martinez- University of twist-bend nematic phase Paterson Felipe, R. Walker, Aberdeen transition J. M. D. Storey, and C. T. Imrie

PI 1 Liquid-Crystal-Directed Nano-Assemblies

Linda Hirst UC Merced, University of Califormia

Experiments and theory focused on understanding the interactions between nanoscale particles and liquid crystal fluids has been a recent area of growth in the field, in particular in the context of improving nano-particle dispersions to produce stable composite materials. Another promising direction has been to take advantage of liquid crystal phases to induce spatial organization of nano-particles by a bulk assembly method. I will review recent work in these two areas by our group and others, in particular looking at a new methodology developed in our lab to form nano particle membranes and capsules using mesogen- functionalized quantum dots.

PI 2 Structure and Lyotropic Liquid-Crystalline Phase Behaviour of Lipid Membranes

J.M. Seddon a aChemistry Department, Imperial College London, Exhibition Road, London SW7 2AZ, UK

Lyotropic liquid crystals of 1-, 2-, or 3-dimensional periodicity spontaneously assemble when lipids are mixed with solvent under various conditions of temperature, pressure and hydration. Although biomembranes are generally based on the fluid lamellar phase, there is increasing evidence that curved membrane structures such as the inverse cubic phases may be present in cell membranes, and/or may facilitate cellular processes such as endo- and exocytosis, and fusion. We have studied the effect of chain branching on the phase behaviour of a series of synthetic β-D- glucosides derived from Guerbet alcohols, whose total hydrocarbon chain length ranged from C8 to C24. A wide range of liquid-crystalline phases was observed, with the C16 Guerbet glucoside (i.e. - Glc-C10C6) forming an Ia3d cubic phase of space group in excess aqueous solution, which is very unusual behaviour. Monoacylglycerols have proved to be invaluable for in-cubo crystallization of membrane proteins. We have studied the effect of hydrostatic pressure on the L – Ia3d cubic transition of monolinolein at a range of hydration. Pressure is found to stabilize the lamellar phase over the cubic phase, and at fixed pressure, increasing the water content causes the coexistence region to move to lower temperature. We have previously shown that by addition of weakly-polar amphiphiles such as diacylglycerols to phospholipids, one can tune the interfacial curvature to be strongly inverse, leading to the formation of a discontinuous cubic phase of spacegroup Fd3m, with a structure based upon a complex close packing of inverse micelles. We have investigated the effect of hydrostatic pressure on the structure and stability of this phase, and have discovered a number of novel effects. We also discovered a lyotropic phase of space group P63/mmc, whose structure is based upon a 3-D hexagonal packing of quasi-spherical inverse micelles, in a hydrated mixture of dioleoylphosphatidylcholine, dioleoylglycerol, and cholesterol. We discovered a novel inverse ribbon phase in the branched-chain polyoxyethylene surfactant system tetradecyloctadecyl-tetraoxyethylene ether (C14C16EO4) in excess water. This phase is stabilised by the application of hydrostatic pressure. The lattice parameters of the inverse ribbon phase were found to vary with pressure, with the structure becoming increasingly distorted away from 2-D hexagonal symmetry (b/a = √3) with increasing pressure.

PI 3 Understanding unusual electric field-driven reorganisations in the mesophases of bent-core liquid crystals

M. Nagaraj aSchool of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

Although usually associated with rod or disk like molecules, liquid crystal phases have been observed for organic molecules with a variety of different and unconventional anisotropic shapes. Amongst these, bent-core mesogens have been considered as one of the most fascinating classes due to their wide range of unique mesophases and unusual physical properties not exhibited in more conventional liquid crystals. Indeed, even the well-known nematic phase formed by bent-core molecule, exhibits distinct physical properties such as enhanced cybotacticity, anomalous elastic constants, and large flexoelectricity and spontaneous deracemization, to name just a few.

I will present some of the unusual electric field-driven transformations seen in the lamellar mesophases formed by bent-core molecules. This will mainly include SmAPR/A/F, SmCS/APA/F and dark conglomerate phases. Particularly, a detailed investigation of an unusual DC phase observed in an oxadiazole based achiral BCLC will be described. The DC phase exhibits amazing physical properties, including an electric field tuneable chiral domain structure [1,2] and a large reduction of refractive index [3,4], while maintaining an optically dark texture when observed under crossed polarisers. The transformations are seen irrespective of the frequency of the applied electric field, type of the waveform and the thickness or the geometry of the device used. The nature of the behaviour has been investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy and small angle X-ray scattering. Based on the results, a model of the DC phase will be described where in the ground state the nanostructure of phase exhibits an anticlinic antiferroelectric organization. Under an electric field, it undergoes a molecular rearrangement without any gross structural changes leading to an anticlinic ferroelectric order while keeping the overall sponge-like structure of the DC phase intact.

References 1M. Nagaraj, K. Usami, Z. Zhang, V. Görtz, J. W. Goodby and H. F. Gleeson, Liq. Cryst. (2014), 41, 800. 2M. Nagaraj, J. C. Nones, V. P. Panov, H. Liu, G. Portale, W. Bras and H. F. Gleeson, (2015) submitted. 3H. E. Milton, M. Nagaraj, S. Kaur, P. B. Morgan, J. C. Jones and H. F. Gleeson, Appl. Optics (2014), 53, 7278.

4M. Nagaraj, V. V. Görtz, J. W. Goodby and H. F. Gleeson, Appl. Phys. Lett. (2014), 104, 0219031

PI 4 From biaxiality to bistability, and back again.

J. Cliff Jones

School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

Having spent over thirteen years as C.T.O. of the spin-out company ZBD Displays that I had helped found, I join academia to find a topic of great interest to me in my earlier career, biaxiality in liquid crystal systems, has become important again. My early work, as George Gray’s last Ph.D. student in Hull University, whilst working with Peter Raynes at R.S.R.E. in Malvern, had been on studying the biaxial refractive indices and permittivities of the smectic C phase. Indeed, I showed that the large dielectric biaxiality was responsible for the slowing of latching response times with increasing field in surface stabilised ferroelectric liquid crystal devices. Understanding this led to major breakthroughs in FLC for display applications, culminating in the demonstration of HDTV performance in a passive matrix addressed display working with the Sharp Corporation in Japan and Sharp Laboratories Europe in the mid-1990s.

In addition to biaxiality, FLC had the useful property of bistability where either of two states is retained after an addressing pulse is applied allowing complex displays to be addressed line by line without a thin-film-transistor at each pixel. Given the difficulties of obtaining and maintaining uniform FLC alignment, an obvious approach was to induce bistability in a conventional nematic. The only bistable nematic device to be commercialised is the zenithal bistable display or ZBD. This uses deep homeotropic surface relief structures to induce both bistable states and a flexoelectric polarisation. The commercial devices produced by the spin-out company ZBD Displays Ltd (now Displaydata) latch in 500microseconds at 2Vm-1. They are constructed at low cost using embossing to form a bistable twisted nematic / hybrid nematic device. After perfecting the manufacturing processes and developing a novel RF communication protocol, Displaydata has sold millions of displays worldwide in electronic-shelf-edge labels for the retail sector.

Now in joint work with Helen Gleeson at Leeds and Mamatha Nagaraj at Manchester, my interest in biaxiality has been re-ignited. In particular, the dark-conglomerate phase observed in certain bent- core materials undergoes unusual changes in refractive index that are due to the biaxial nature of the materials. As with the ferroelectric liquid crystals and the grating aligned nematics before them, these phases have great potential for future device applicatons.

PI 5 Solid Liquid Crystals

Mark Warner Cavendish Laboratory, University of Cambridge, UK

Liquid crystals revolutionise both solid body mechanics and the seemingly impossible goal of achieving Gaussian curvature from flat spaces. SLCs arise from networks:  As elastomers, that is rubbers, where fluidity and director mobility are preserved  As glasses, that is strong solids where the director only “convects” with deformation.

Both types of solids lack positional order, but their LC anisotropy and possible complexity in their director fields give unique phenomena in mechanics, topology and topography.

I 1 What does a Liquid Crystal Do in a Gyroid? T J Athertona aDepartment of Physics and Astronomy, Tufts University, Medford, MA 02155

Nematic liquid crystals in confined systems adopt a distorted configuration to comply with the surface anchoring conditions. Compatibility between the symmetry of the nematic order and the topology of the confined system necessitates the introduction of defects; the number and placement of these defects must then be determined by energetic considerations. A familiar example is that of a nematic confined to lie tangentially to the surface of a sphere: in this case, a total defect charge of +2 is required to accommodate the curvature by the Gauss-Bonnet theorem. The ground state is found to be a tetrahedral configuration of +1/2 defects. Here, we study a related problem: what does a nematic do when confined to a gyroid structure? The gyroid is a triply-periodic minimal surface that partitions space into two disconnected regions. When one of the regions is filled with nematic liquid crystal, the presence of curvature enforces the presence of defects and, intriguingly, the equilibrium structures break chiral symmetry. We present our simulations of these structures—an example is shown in the figure above—and study the effect of material and anchoring parameters on the configurations obtained.

I 2 Myelin 19th century microscopy, giant squid (and a duel with Bismarck). John Lydon Faculty of Biological Sciences,The University, Leeds, LS2 9JT [email protected]

Exterior

ro ro

rs rn rn

ri ri

Interior Lipids have a variety of roles in biological systems. In all living organisms, phospholipid bilayers form the membranes which encompass the cells (and the organelles within them), and the ultimate food stores in animals are deposits of fat. Myelin, the white, lipid/protein mixture which sheathes nerve fibres in higher animals, has a unique, and very different role to these. It is an electric insulator, enhancing the speed at which impulses travel along nerve axons. For completely myelinated axons the velocity can be as high as 12 m/sec. Without the myelin sheath this would be reduced by factor of at least 10. In a world where response times can determine survival rates, large animals would be at a severe evolutionary disadvantage without it. In humans, depletion or damage to myelin layers can cause a variety of conditions, including multiple sclerosis and schizophrenia.

When nerve tissue is placed in water it swells to a remarkable extent, producing ‘myelin figures’, elongated finger-like growths which writhe like living material as they extend. This startling phenomenon was first recorded in 1854, (34 years before Reinitzer’s cholesteryl esters) and is arguably the first indication of liquid crystalline phases, [1, 2, 3]. This pioneering work took place in Prussia at a time of great social upheaval and intense political activity. One of foremost workers irritated the government with his liberal views to the extent that he found himself challenged to a duel by the Iron Chancellor himself [4]. Interesting times indeed.

References [1] R. Virchow, Über das ausgebreitete Vorkommen einer dem Nervenmark analogen Substanz in den tierischen Geweben, (On the widespread distribution in animal tissues of a substance analogous to nerve marrow), Virchows Arch. Pathol. Anat.) 1854, 6 (4): 562–72. doi:10.1007/BF02116709 [2] O. Lehmann, Über Contactbewegung und Myelinformer (On contact motion and myelin formation), 1895, Weidemann’s Annalen fur Physik und Chemie 56, 771-788. [3] D. Dunmur and T. Slukin, Soap, science and flat screen TVs - a history of liquid crystals, Oxford University Press, 2011, pages 124, 130 134, 280 293. [4] G.A.Silver, (1987). "Virchow, the heroic model in medicine: health policy by accolade". American Journal of Public Health 77 (1): 82–88. doi:10.2105/AJPH.77.1.82. PMC 1646803. PMID 3538915.

T 1 Colloids in Blue Phase Liquid Crystals A.C. Pawseya,b ,Paul. S. Clegga aSUPA, School of Physics and Astronomy, JCMB, Peter Guthrie Tait Road EH9 3FD, Edinburgh, UK bRowett Institute of Nutrition and Health, Greenburn Road,Bucksburn, Aberdeen, AB21 9SB, UK

Colloid–liquid crystal composites are an exciting class of responsive, soft materials. Colloidal particles mixed into liquid crystals create defects in the (ideally defect free) ordered phase. The form of the defects is dependent on the particle size, the alignment of the mesogens at the particle surface and how strongly this alignment is enforced (the anchoring strength).

Highly chiral LCs have delicate phases formed from an ordered arrangement of defect lines. These cholesteric blue phases normally only appear in a narrow window of temperature and chirality due to the delicate balance between satisfying an increased degree of twist with the expense of creating defect lines.

We add micron-sized colloids to a chiral nematic LC with a blue phase as a means to study the effect of disorder on the phase transitions of a system already dominated by defects. The colloids are a source of disorder, disrupting the liquid crystal as the system is heated from the cholesteric to the isotropic phase through the blue phase. The colloids act as a preferential site for the growth of BPI from the cholesteric; in high chirality samples BPII also forms. In both BPI and BPII the colloids lead to localised melting to the isotropic, giving rise to faceted isotropic inclusions. This is in contrast to the behaviour of a cholesteric LC where colloids lead to system spanning defects.

References: 1) A. C. Pawsey, P. S. Clegg, (2015) Soft Matter DOI: 10.1039/c4sm02131b

T 2 Computer simulations of an anionic chromonic dye: spontaneous symmetry breaking to form chiral aggregates and the formation of a novel smectic phase

omnik Thind1, Mark R. Wilson1

1Department of Chemistry, Durham University, Durham, DH1 3LE, UK Corresponding author e-mail: [email protected]

Controlling self-assembly of nanostructured soft matter in aqueous solution is of considerable interest in the formation of thin organic films and in future organic electronics applications. Interpretation of experimental findings for the anionic chromonic dye (figure 1), has lead to the proposal of two self-assembled structures not typically observed for chromonic systems, with a double- width column arrangement for the nematic region, and the transition to a non-columnar layer structure at higher concentrations. The deviation of these proposed models Figure 1: Structure of an anionic from the more common behaviour of chromonic chromonic dye mesogens, to favour a direct face-to-face aromatic stacking to form columns, has to lead to speculation as to how energetically feasible these more rare motifs are.

Molecular dynamics simulations at a fully atomistic level are able to provide a “picture” of the preferred stacking structure within chromonic aggregates in aqueous solution [1]. A new interpretation for experimental results is provided, with low concentrations of the anionic dye (figure 1) showing spontaneous symmetry breaking, wherein chiral aggregates (figure 2) form as the energetically most stable species. This is despite the presence of a strictly achiral dye mesogen.

Results for higher concentrations show the alignment of several aggregates to form a novel biaxial-smectic layer structure, with the inherent loss of chirality as a result of this new molecular environment. The formation of the novel layer structure, which is stabilized by interactions of surface charged groups explains key Figure 2: Chiral aggregates experimental findings, as well as retaining the more common of an anionic dye columnar stacking found in typical chromonic systems.

Summary: Atomistic molecular dynamics simulations have provided evidence for: (i) the spontaneous self-assembly of achiral molecules in solution to form chiral aggregates, (ii) a novel biaxial-smectic chromonic phase not seen previously.

References [1] F. Chami and M. R. Wilson, J. Am. Chem. Soc., 132, 7794-7802 (2010)

T 3 Design and investigation of a gold nanoparticle side-chain liquid crystal polymer nanocomposite

O. Amos and G. H. Mehl

Department of Chemistry, University of Hull, HU6 7RX, UK

Metal nanoparticle functionalized liquid crystalline materials have attracted considerable attention due to their potential applications in magnetic, optical, electronic devices and as catalysts. The optical and magnetic properties of these nanoparticles are of high interest and this related to the potential of 2D and 3D organisation of such materials. Research on the organic groups for such systems has concentrated mainly on the type of the mesogenic groups selected and to some extend on the functional groups linking the NPs and the mesogens1,2. A parameter which has been investigated in less detail, with the notable exception of some dendritic mesogens3,4 is the size of the organic corona. Here we present our results on the investigation of gold NPs where side-chain LC polymer chains (SCLCPs) have been attached to the NPs. The synthesis of these systems was explored systematically. The length of the chains and the number of mesogenic groups were varied systematically. The preparation of SCLCPs, either by grafting to the NPs or by polymerisation from the preparation of an Au-NP macroinitiator were explored. The mode of polymerisation either free radical polymerisation or atom transfer radical polymerisation (ATRP) was varied5-9. The results of the synthetic work will be presented and the chemical characterisation by NMR. GPC and MALDI-TOF and TEM of the AuNP-SCLCP nanocomposites will be reported. The results of the investigations of the LC properties of these systems, based on OPM, DSC and XRD investigations will be presented. The properties of these systems will be discussed and will be compared to structurally related materials.

References

1. S. Umadevi, X. Feng and T. Hegmann, Adv. Funct. Mater. 2013, 23, 1393-1403 2. M. Mojcik, W. Lewandowski, J. Matraszek, J. Mieczkowski, j. Borysiuk, D. Pociecha, E. Gorecka, Angew. Chem. Int. Ed. 2009, 48, 5167-5169

3. B. Donnio, P. G. Vázquez, J. L. Gallani, D. Guillon, and E. Terazzi, Adv. Mater. 2007, 19, 3534–3539 4. K. Kanie, M. Matsubara, X. B. Zeng, F. Liu, G. Ungar, H. Nakamura and Muramatsu, J. Am. Chem. Soc., 2012, 134, 808-811 5. W. A. Braunecker, K. Matyjaszewsi, Prog. Polm. Sci., 2007, 32, 93-146 6. N. J. Warren, C. Muise, A. Stephens, S. P. Armes, and A. L. Lewis Langmuir, 2012, 28 (5), 2928–2936 7. K. Matsura, K. Ohno, S. Kagaya, H. Kitano, Macromol. Chem. Phys., 2007, 208, 862-873 8. A. D’Annibale, L. Ciaralli, M. Basseti, C. J. Pasquini, J. Org. Chem., 2007, 72, 6067–6074 9. G. Hughes, M. Kimura, S. L. Buchwald, J. Am. Chem. Soc., 2003, 125,11253-11258

T 4

A combined experimental and computational study of anthraquinone dyes as guests within nematic liquid crystal hosts

M. T. Sims, L. C. Abbott, S. J. Cowling, J. W. Goodby, and J. N. Moore

Department of Chemistry, The University of York, Heslington, York, YO10 5DD, UK

The use of dye molecules within liquid crystal hosts has been studied in the past for a wide variety of different dyes and host mixtures, and explored for the development of a range of practical devices. The potential applications of such systems are widespread, with the focus often being on guest-host display devices, and they may offer benefits over traditional liquid crystal displays.

For guest-host applications, the alignment of guest dye molecules within a liquid crystal host is important for the development of practical devices, and other factors such as the dye colour, absorption strength, and stability also need to be considered. Hence, it is desirable to obtain a detailed knowledge of the structure and properties of dye molecules proposed for such applications, and to rationalise their behaviour in liquid crystal hosts.

We have been studying anthraquinone dyes with a range of colours, including some phenylamine and phenylsulfide disubstituted systems drawn from a class which have been relatively widely studied, as well as some recently synthesised directly arylated systems.1

Our UV-visible absorption studies of these dyes in the nematic host mixture E7 have provided experimental dichroic ratios of the dyes, which give significant differences in their observed order parameters. We have also been carrying out computational studies, including density functional theory calculations on the dyes, yielding insights into the basis of the observed differences in colour and the natures of the electronic transitions giving rise to their visible absorption bands. Fully atomistic molecular dynamics simulations of the guest-host systems have enabled the molecular alignments within the host to be assessed, and, in combination with the DFT calculations, have provided a direct comparison with the experimental dichroic ratios.

References 1. S. J. Cowling, C. Ellis, and J. W. Goodby, Liquid Crystals, 38: 1683–1698 (2011).

T 5 Multiscale models of metallic inclusions in nematic liquid crystals

T.P. Bennetta , G. D’Alessandroa K.R. Dalyb a Mathematical Sciences, University of Southampton, Southampton, England, UK b Engineering Sciences, University of Southampton, Southampton, England, UK

Suspension of nanoparticles in liquid crystals have been modelled on a range of scales, from molecular simulations [2] to macroscopic models [3]. The former are computationally expensive and only a few particles can be modelled. The second rely on macroscopic parameters whose values are not determined self-consistently. In previous work [1] we have derived equations governing a nematic liquid crystal hosting fixed metallic inclusions with weak anchoring conditions. In this case we obtained macroscopic governing equations containing effective material parameters that are related to the microscopic geometry by a series of cell problems. These describe the local effect of a single nanoparticle on the liquid crystal alignment and electric field based on the assumption that the nanoparticles are evenly distributed and, hence, the underlying geometry is approximately periodic. We obtain good agreement between finite element simulations of a planar cell containing ellipsoidal inclusions and our macroscopic model as shown in figure 1. In the weakly interacting regime, i.e.

small anchoring energy and/or low concen- 2 1 trations, the liquid crystal director is de- (a) (b)

termined by a balance between the bulk

[rad] [rad]

forces in the liquid crystal and the align-

)

)

θ

θ

ment at the boundary of the device and 1 0.5

−

−

at the nanoparticles. In this regime, /2

the macroscopic equations for the direc- /2 (π tor alignment contain three key differences (π with respect to those for a pure liquid crys- 0 0 tal: (i) the elastic constants are in general 0 16 32 0 16 32 smaller, (ii) there is a forcing term pro- z [µm] z [µm] portional to the anisotropy of the parti- cles and, (iii) the dielectric susceptibility Figure 1: Verification of our model for a 32 cell system, each cell con- of the system is altered due to the fringe tains a single ideal metallic particle. Red points are from homogeniza- fields created by the metallic particles. tion, broken black line corresponds to a pure liquid crystal, and blue line We are in the process of extending this is from COMSOL finite element simulations. Left panel shows spherical work to include particles that are free to particles of radius r = 0.3 µm at 1.5 and 3 Volts. Right panel ellipsoidal rotate. The motion of the particles and ne- particles with semi axes 0.1 and 0.3 µm at zero applied field for different matic is modelled using a dissipation prin- anchoring energies. ciple [4]. We discuss the derivation of the equations, provide an interpretation of the terms driving the reorientation of the particles and discuss how this approach can be used to study the effects of freely rotating particles on the dynamics of the liquid crystal. For example the effective anisotropic fields induced by the particles become time dependent.

References

[1] T. P. Bennett, G. D’Alessandro, and K. R. Daly, Multiscale models of colloidal dispersion of particles in nematic liquid crystals, Phys. Rev. E, 90 (2014), p. 062505.

[2] B. T. Gettelfinger, J. A. Moreno-Razo, G. M. Koenig Jr, J. P. Hernandez-Ortiz, N. L. Abbott, and J. J. de Pablo, Flow induced deformation of defects around nanoparticles and nanodroplets suspended in liquid crystals, Soft Matter, 6 (2010), pp. 896–901.

[3] L. M. Lopatina and J. V. Selinger, Theory of Ferroelectric Nanoparticles in Nematic Liquid Crystals, Phys. Rev. Lett., 102 (2009), p. 197802.

[4] A. Sonnet, P. Maffettone, and E. Virga, Continuum theory for nematic liquid crystals with tensorial order, J. Non-Newtonian Fluid Mech., 119 (2004), pp. 51 – 59.

T 6 Further tricritical and antinematic behaviour in a revisited mildly repulsive Straley model F. Bisia , G. De Matteisb and S. Romanoc aDipartimento di Matematica “F. Casorati”, Università di Pavia, via A. Ferrata, 1, 27100 Pavia, Italy bDepartment of Mathematics and Information Sciences, Northumbria University, Camden Street, NE2 1XE, UK cDipartimento di Fisica “A. Volta”, Università di Pavia, via A. Bassi 6, 27100 Pavia, Italy

We consider biaxial nematogenic lattice models, involving particles of D2h symmetry, whose centres of mass are associated with a three–dimensional simple-cubic lattice. The pair potential is isotropic in orientation space and restricted to nearest neighbours. Let two orthonormal vector triads define orientations of a pair of interacting particles. The investigated potential models are quadratic with respect to the nine scalar products between the two sets of unit vectors. Available geometric duality transformations allow to reduce these expressions to diagonal form containing only the scalar products between corresponding unit vectors and depending on three coupling constants. The resulting potential is known in the literature as the generalised Straley model. By now, various sets of values of the free model parameters have been studied and they are capable of producing both calamitic and antinematic phases, both biaxial and uniaxial phases, both first– and second–order phase transitions. Here, we further pursue the analysis in terms of a molecular-field approach and a Monte Carlo simulation study of a family of potential models, namely the μ models, put forward in [1]. In these models, two predominant calamitic couplings of equal strength (−2) are perturbed by a comparatively weaker antinematic one, parameterised by a coupling constant 1+μ, where μ ranges in [0, 1]. It has been shown in [1] that for μ sufficiently small the model predicts second–order transitions to the biaxial nematic phase from both the isotropic and the uniaxial phases. The models, further explored here, unveil first–order transitions from the uniaxial to the biaxial phase, thus disclosing a tricritical behaviour. The change of order sets in at values of μ close to 1 where the antinematic coupling constant become comparable with the calamitic ones. An adapted Monte Carlo computational procedure allowed differentiating between ordering of the three molecular axes, the ones calamitically and the ones antinematically coupled, so to speak, and to detect a change in the order of transition from the uniaxial to the biaxial phase in the low temperature regime. On the other hand, a molecular–field approach in the asymptotic regime (μ approaching 1) has confirmed the same tricritical behaviour.

References [1]G. De Matteis and S. Romano, Phys. Rev. E 78, 021702 (2008).

T 7 Origin of Chirality in the Triple Network Tri-continuous Cubic Phase Formed by Achiral Rod-like Molecules X. B. Zenga, G. Ungara, F. Liub, C. Dresselc, M. Prehmc and C. Tschierskec aDepartment of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK b State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, P. R. China c Institute of Chemistry, Organic Chemistry, Martin-Luther-University Halle-Wittenberg, 06120 Halle, Germany a e Two cubic phases, formed by infinite interpenetrating molecular networks, have been known in thermotropic liquid crystals for years. They are the “double gyroid” phase with two networks (symmetry Ia3d), and the “triple network” phase with three networks (symmetry 1 b c Im3m) . However, it has only been discovered recently by polarized optical microscopy and CD f spectroscopy that, despite being formed from achiral rod-like molecules, the triple-network d cubic phase (Im3m) is always chiral, while the double-network (Ia3d) phase is always achiral2. These intriguing observations are explained by propagation of homochiral helical twist across the entire network through helix matching at network junctions. In the Ia3d phase the opposing chiralities of the two networks cancel, g h i j but not so in the triple-network Im3m phase (Figure 1). The high twist in the Im3m phase explains its previously unrecognized chirality, as well as the origin of this complex structure and I II the transitions between different cubic phases.

Figure 1. (a) The two networks (red and blue) of the Ia3d phase decorated with schematic mesogens (rod- like molecular cores, green) showing the molecular twist along the network segments. The gyroid minimum surface is also shown (yellow). (b) The same but for the middle of the three networks of the Im3m phase .This network closely follows the Schwartz P-type minimum surface (shown in yellow). (c) The middle network shown as ribbons containing the molecular axes (black rods). (d-f) Detailed network junctions in ribbon representation for the Im3m phase.

References 1 X. B. Zeng, G. Ungar and M. Imperor-Clerc, Nat. Mater. (2005), 4, 562 – 567. 2 C. Dressel, F. Liu, M. Prehm, X. B. Zeng, G. Ungar and C. Tschierske, Angew. Chem. Int. Ed. (2014), 53, 1 – 7.

T 8 Coarse Grained Modelling of the Phase Behaviour and Structure of Non-Ionic Surfactants with the SAFT- force field O. Lobanova, C. Herdes, E. A. Müller, and G. Jackson Department of Chemical Engineering, Centre for Process Systems Engineering, South Kensington campus, Imperial College London, London SW7 2AZ, United Kingdom

An application of the “top-down” concept for the development of accurate coarse-grained intermolecular potentials of complex fluids from an algebraic equation of state is used in the context of aqueous solutions of non-ionic surfactants. In our approach, we use a recent implementation of the statistical associating fluid theory of variable range (SAFT-VR) [1], and its group-contribution formulation (SAFT- to develop effective coarse-grained force fields based on the Mie (generalised Lennard- Jones) potential. Fluid-phase equilibrium properties such as the vapour pressure and saturated liquid density are used to efficiently estimate the parameters of the coarse- grained Mie force field over a broad range of thermodynamic conditions with the aid of the algebraic equation of state [3]. The SAFT-γ coarse-grained models can then be used in direct molecular simulation to describe properties which were not used to develop the potential model such as the enthalpy of vaporisation, interfacial tension, density profiles, supercritical densities, and other thermodynamic, structural, and transport properties. The versatility of the procedure has been

demonstrated for carbon dioxide (CO2) [4] and other green-house gases [5], n-alkanes [5], alkylbenzenes [6], and water [7]. Here we develop a generic CG force field for aqueous solutions of alkylpolyoxyethylene (CiEj) non-ionic surfactants. Although the parameterisation for the different chemical moieties is carried out to match the thermodynamic bulk properties of representative compounds (alkanes, alkyl ethers, gylcols), the SAFT-γ force field is found to be robust and transferable allowing for the prediction of the key structural, interfacial and kinetic properties of the surfactant solution. The spontaneous formation of micelles at low surfactant concentrations is observed as well as expected self-assembly into bilayer at high surfactant concentrations. Members of the CiEj family of varying alkyl and ethoxy chain length are investigated to assess the transferability of the model. The aggregation numbers, critical micelle concentrations, as well as surfactant area and bilayer thickness are found in a good agreement with experimental data.

References [1] T. Lafitte, A. Apostolakou, C. Avendaño, A. Galindo, C. S. Adjiman, E. A. Müller, and G. Jackson, J. Chem. Phys. 139, 154504 (2013). [2] V. Papaioannou, T. Lafitte, C. Avendaño, C. S. Adjiman, G. Jackson, E. A. Müller, and A. Galindo, J. Chem. Phys.140, 054107 (2014). [3] E. A. Müller and G. Jackson, Ann. Rev. Chem. Biomol. Eng. 5, 405 (2014). [4] C. Avendaño, T. Lafitte, A. Galindo, C. S. Adjiman, G. Jackson, and E. A. Müller, J. Phys. Chem. B 115, 11154 (2011). [5] C. Avendaño, T. Lafitte, C. S. Adjiman, A. Galindo, E. A. Müller, and G. Jackson, J. Phys. Chem. B 117, 2717 (2013). [6] T. Lafitte, C. Avendaño, V. Papaioannou, A. Galindo, C. S. Adjiman, G. Jackson, and E. A. Müller, Mol. Phys. 110, 1189 (2012). [8] O. Lobanova, C. Avendaño, E. A. Müller, and G. Jackson, Mol. Phys. (2015) DOI:10.1080/00268976.2015.1004804 (2015).

T 9 Synthesis and properties of asymmetric dimeric materials with lateral and terminal fluorine substituents for dual frequency liquid crystal mixtures David Allan and M. Hird Department of Chemistry, University of Hull, Hull HU6 7RX, UK

Nematic liquid crystals have been widely used in electro-optical devices due to the ability to switch the orientation of materials using an external electric field. In conventional device, while the switch- on response time can be decreased by increasing the electric field, the switch-off relaxation process is much slower.[1]

With the continuing requirement for faster switching times and alternative route can be found in dual frequency liquid crystal materials (DFLCs). Usually DFLC materials are a two component mixture, positive compounds with a positive dielectric anisotropy that decreases at higher frequencies and negative compounds with a large negative dielectric anisotropy that remains almost constant across different frequencies.[1]

A liquid crystal dimer is a material with two mesogenic core units separated by a flexible spacer, usually alkyl chains. Dimers have been the target of a great deal of research due to the unusual liquid crystal behaviour they exhibit.[2]

A series of asymmetric dimeric materials have been targeted, these feature one core unit with lateral fluorine substituents and the other core with terminal fluorination. The aim is to synthesise materials with one core contributing to positive dielectric anisotropy and the other negative dielectric anisotropy. The synthesis of a series of fluorinated dimers is described. With the mesomorphic properties characterised by OPM, DSC and XRD.

References: [1] H. Xianyu, S.-T. Wu, and C.-L. Lin, Liquid Crystals, 2009, 36, 717–726. [2] C. T. Imrie and P. A. Henderson, Curr. Opin. Colloid Interface Sci., 2002.

T 10 Liquid crystal dimers: A molecular level and mesoscale study Martin Walker and Mark Wilson* Department of Chemistry, Durham University, Durham, DH1 3LE, UK

Liquid crystal dimer molecules exhibit a puzzling, and as yet, not fully characterised phase transition between the nematic and smectic phases. This new phase was originally denoted the Nx phase to highlight its unknown nature. The Nx phase is commonly interpreted using one of two theories: that the phase is a twist-bend nematic NTB (where the nematic director both twists and bends, resulting in a helical director structure with a singular nematic order parameter), or a pre-transitional cybotactic nematic (where small, unaligned smectic domains give rise to an overall (biaxial) nematic order parameter).

To help elucidate the structure of the Nx phase, we have simulated liquid crystal dimer molecules using a coarse-grained methodology, which allows a large number of dimer molecules to be studied (105 molecules) for the first time.

We have found both a stable nematic and smectic phase. Between these two well established phases we find another stable mesophase that is neither nematic nor smectic, but maintains features of both phases. In this “Nx phase”, the bent nature of the dimer molecule imposes a small bend between layers that are otherwise locally smectic. This removes any long range ordering of layers. This behaviour can only be seen in large simulations, where we are able to look at more than the local order seen in previous small atomistic simulations [1], and analyse molecular order in more depth.

Nx

[1] Chiral heliconical ground state of nanoscale pitch in a nematic liquid crystal of achiral molecular dimers, 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, J. E. Maclennan, and N.A. Clark, Proc. Nat. Acad. Sci., 2013, 110, 15931–15936.

T 11 Raman scattering studies of orientational order parameters in liquid crystalline dimers exhibiting conventional and twist-bend nematic phases

Vitaly P. Panov,a Zhaopeng Zhang,a , Mamatha Nagaraj,a Richard J. Mandle,d John W. Goodby,d Geoffrey R. Luckhurst,c J. Cliff Jonesa,b and Helen F. Gleesona,b

aSchool of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK bSchool of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK cChemistry, University of Southampton, Highfield, Southampton SO171BJ, UK dDepartment of Chemistry, University of York, York YO10 5DD, UK

Liquid crystalline dimers have recently attracted significant attention due to the intriguing properties of the twist-bend nematic phase (NTB), discovered in dimers with an odd number of carbon atoms in the linking alkyl chain1,2,3. Understanding both the physical properties of the twist-bend phase and its relationship to the conventional nematic phase (N) is of significant interest. We have used Polarised Raman Spectroscopy (PRS) to quantify the orientational order in both of the nematic phases that occur in certain liquid crystalline dimers. PRS is a particularly powerful way of determining order parameters as both 〈푃2〉 and 〈푃4〉 order parameters can be determined4 A series of compounds has been investigated

0.8 with alkyl chain lengths of 7, 8, 9 and 11 5CB 8CB 0.7 carbons connecting two cyanobiphenyl

0.6 =0.981 mesogenic groups. The nature of the Raman NI

0.5 T/T spectra has been investigated across the

0.4 =0.982 temperature range, including the N and N

TB

NI

=0.980

NI

=0.984

=0.980

T/T

=0.982 NI

0.3 NI phases, where it was found that the Raman

T/T

NI

T/T

T/T T/T

Order Parameters Order 0.2 peaks do not show a significant change in 0.1 wavenumber, even across the NTB-N phase 0.0 transition. Both 〈P2〉 and 〈푃4〉 order parameters 7 8 9 10 11 n value for CB-Cn-CB have been determined across the N phase range. Measurements were also made into the NTB phase just below the NTB - N phase transition where a uniform NTB texture can be maintained. In the N phase, the odd dimers exhibit rather low order parameters with 〈푃2〉 taking values between 0.3 and 0.5 and 〈푃4〉 about 0.25, in keeping with their bent shape. In contrast, the even dimer shows extremely high values of the order parameters with 〈푃2〉 between 0.7 and 0.8 and 〈푃4〉 between 0.4 and 0.45. For the odd dimers, the values of 〈푃2〉 in the NTB phase are similar to those of the N phase, while 〈푃4〉 jumps by approximately 5-10% and changes its temperature dependence. On comparing the results with the predictions of a molecular field model, we find good agreement for the elongated molecules of the even dimer. The odd dimers, however, show higher 〈푃4〉 values than that obtained from the model, also as might be expected for molecules having predominantly bent conformations.

1 M. Šepelj, A. Lesac, U. Baumeister, S. Diele, H. L. Nguyen and D. W. Bruce, J. Mater. Chem., 2007, 17, 1154. 2 V. P. Panov, M. Nagaraj, J. K. Vij, Y. P. Panarin, A. Kohlmeier, M. G. Tamba, R. A. Lewis and G. H. Mehl, Phys. Rev. Lett., 2010, 105, 16780. 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, J. Salud, B. A. Timimi and H. Zimmermann, Phys. Rev. E, 2011, 84, 031704. 4 C D. Southern and H. F. Gleeson, Eur. Phys. J. E 2007, 24, 119.

T 12 Complex Rheology of Nematogenic Fluid; Connection to Elastic Turbulence

B. Chakrabarti, R. Mandal, D. Chakraborty, and C. Dasgupta

Department of Mathematical Sciences, Durham University, Durham, DH1 3lE, UK

Rheological chaos and Elastic turbulence are two phenomena that have attracted a lot of attention in recent years. Motivated by experiments that probe statistical quantities of these two phenomena we numerically analyse the full non-linear hydrodynamic equations of a sheared nematic fluid under shear stress and strain rate controlled situations incorporating spatial heterogeneity in the gradient direction. For a certain range of imposed stress and strain rates, this extended dynamical system shows signatures of spatio-temporal chaos and transient shear banding. In the chaotic regime the power spectra of the order parameter stress and the total injected power shows power law behavior and the total injected power shows a non-Gaussian, skewed probability distribution, which bear striking resemblance to elastic turbulence phenomena observed in polymer solutions. The scaling behavior is independent of the choice of shear rate/stress control method.

References [1] Chakrabarti, B, Das, M, Dasgupta, C, Ramaswamy, S & Sood, AK (2004). Spatiotemporal rheochaos in nematic hydrodynamics. Physical Review Letters 92(5). [2] Das, M, Chakrabarti, B, Dasgupta, C, Ramaswamy, S & Sood, AK (2005). Routes to spatiotemporal chaos in the rheology of nematogenic fluids. Physical Review E 71(2). [3] Mandal, R., Chakrabarti, B., Chakraborty, D. & Dasgupta, C. (2014). Complex Rheology of Nematogenic Fluid; Connection to Elastic Turbulence. http://arxiv-web3.library.cornell.edu/pdf/1406.2575v1.pdf

T 13 Interfacial motion by mean curvature in liquid crystals Amy Spicera, and Apala Majumdara aMathematical Sciences, University of Bath, Bath, BA1 2BL, UK

Nematic liquid crystals are anisotropic orientationally ordered liquids. Working within the Landau- de Gennes theoretical framework, equilibrium nematic configurations are modelled by local or global minimisers of the corresponding Landau-de Gennes energy functional. We adopt the gradient-flow model for dissipative Landau-de Gennes dynamics to study the creation and evolution of nematic-isotropic interfaces in a cylinder, at the nematic-isotropic transition temperature. We impose Dirichlet radial conditions on the lateral surface and numerically study the full parabolic gradient flow system for the Landau-de Gennes Q-tensor in three dimensions, differentiating between planar and non-planar initial conditions with a nematic-isotropic interface structure. Solutions with planar initial conditions retain the nematic-isotropic interface at all times and converge to a uniaxial radial solution with a localized isotropic core around the cylinder axis. Solutions with non-planar initial conditions lose the interface after finite time and converge to an almost uniaxial solution of constant norm.

References 1 L. Bronsard, R. Kohn, Motion by mean curvature as the singular limit of Ginzburg Landau dynamics, Journal of differential equations (1991), 211, 237 2 L. Bronsard, B. Stoth, On the existence of high multiplicity interfaces, Mathematical research letters (1996), 41, 50 3 F. Bethel, H. Brezis, B. Coleman, F. Helein, Bifurcation analysis of minimizing harmonic maps describing the equilibrium of nematic phases between cylinders, Archive for rational mechanics and analysis (1992), 149, 68

T 14 A computationally efficient Q-tensor model with flow for nematic liquid crystals

Murugesan Y.Ka, D’Alessandro Ga, De Matteis Gb

aMathematical Sciences, University of Southampton, Southampton, England, UK; bDepartment of Mathematics and Information Sciences, Northumbria University, Newcastle Upon Tyne, England, UK.

Modelling liquid crystalline flows play a vital role in understanding the non- equilibrium dynamics in active synthetic and biological soft matter systems1 and switching dynamics in liquid crystal based electro-optical devices2. We present a new, computationally efficient method to model the coupled dynamics of flow and alignment of nematic liquid crystals in the absence of defects.

Traditionally, there are two approaches to model liquid crystal alignment with flow. In the Ericksen-Leslie formalism3 the director field is represented with a unit vector n and the alignment dynamics of the director is coupled to the velocity field of the fluid flow. The equations for this vector representation have only one time constant and are, hence, computationally efficient. Alternatively, Sonnet et al4 represent the director field using a 33 traceless, symmetric tensor, the Q-tensor, and obtain the alignment and fluid flow equations from the most generic dissipation function that satisfies the symmetries of the system. This tensor formalism can represent without ambiguity any alignment and embodies the nematic symmetry automatically. Moreover, it takes into account the orientational order of the liquid crystal by including the thermotropic energy in addition to the elastic counterpart. However, due to the difference in magnitudes of the two energy contributions away from a topological defect, the corresponding dynamical equations for the director alignment have two considerably different time scales: the resulting computational model is, hence, very stiff and hard to compute efficiently.

In this talk, we combine the Q-tensor with flow equations of Sonnet et al4 with the multiple time scale approach developed by Daly et al5 and obtain a computationally efficient, one-time-scale model for the orientation of the liquid crystal in the absence of defects. As a validation of our derivation we compare our results with the Ericksen- Leslie theory for 1D planar and twisted nematic cells3 and present numerical simulation of coupled flow and alignment in representative nematic cells.

References 1M. Ravnik and J.M. Yeomans, Phys. Rev. Lett. (2013), 110, 026001. 2A. Tiribocchi, O. Henrich, J.S. Lintuvuori and D. Marenduzzo, Soft Matter, (2014), 26, 4580. 3M.G. Clark and F.M. Leslie, Proc. R. Soc. Lond. A. (1978), 361, 463. 4A.M. Sonnet, P.L. Maffettone, and E.G. Virga, J. Non-Newtonian Fluid Mech. (2004), 119, 51. 5K.R. Daly, G. D’Alessandro, and M. Kaczmarek, SIAM J. Appl. Math. (2010), 70, 2844.

T 15 Rheology of Cholesteric Liquid Crystalline Phases O. Henricha , K. Stratforda , M.E. Catesb and D. Marenduzzob aEdinburgh Parallel Computing Centre, University of Edinburgh, Edinburgh EH9 3FD, UK bSchool of Physics and Astronomy, University of Edinburgh, Edinburgh, EH9 3FD, UK

The flow response in cholesterics is strongly non-Newtonian, highly anisotropic and complex. Theoretical studies showed that a standard cholesteric phase subjected to Poiseuille flow along its helical axis flows mainly through permeation at small pressure differences, leading to high dissipation and very large viscosities. If the helix is oriented along the vorticity direction travelling twist waves appear which cause a rotation of the cholesteric helix. Under higher forcing, the helix uncoils, creating a flow-induced nematic phase. Most of these pioneering results have been derived under specific assumptions like the absence of defects or the constraint that the molecules may only rotate in the flow-gradient plane whilst the orientation of the cholesteric helix remains unchanged 1,2.

Building on our expertise in large-scale simulation of liquid crystals we are able to investigate more general situations. We present new results on the flow of cholesteric fingers and blue phases in microfluidic channels. Depending on the pressure gradient between inlet and outlet, the geometry and anchoring conditions at the channel walls we are able to characterise different flow regimes. These results add to the complex picture that we previously gained from cubic blue phases in simple shear flow3 and contribute to an understanding of the complex flow behaviour of cholesteric phases.

Figure 1: Secondary flow pattern of Blue Phase I in simple shear flow

References 1 A.D. Rey, J. Rheol. (2000), 44, 855. 2 A.D. Rey, J. Rheol. (2002), 46, 225. 3O. Henrich, K. Stratford, P.V. Coveney, M.E. Cates, D. Marenduzzo, Soft Matter (2013), 9, 10243.

T 16 Anisotropic Dielectrophoresis – Nematic Liquid Crystals

A. Saxena*,1 C. Tsakonas,1 I.C. Sage,1 G. McKay,2 N.J. Mottram,2 R.P. Tuffin,3 C.V. Brown1

1 School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham NG11 8NS, United Kingdom 2 Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH, United Kingdom 3 Merck Chemicals Ltd, University Parkway, Chilworth, Southampton, Hampshire SO16 7QD, United Kingdom

Liquid dielectrophoresis describes the phenomenon by which dielectric liquids move to occupy regions of high electric field in response to forces on the electric dipoles in the liquid created by regions of high gradient in the electric field magnitude[1]. Applications that exploit liquid dielectrophoresis effects include switchable microlenses, optical shutters, beamsteerers and diffraction gratings, and electronic paper displays and micro pumps[2,3]. Nematic liquid crystals are attractive for many of these applications because they are often designed to exhibit high permittivity, which provides a high driving force for dielectrophoresis[2]. This is combined with other favourable properties including high refractive index, useful for switchable refractive/diffractive optics applications, plus stability and relatively low viscosity. In a moving nematic liquid crystal film the local orientation of the molecular n-director is determined by balance of torques arising from the direction and magnitude of the applied electric fields, the local flow direction, and the elastic coupling transmitted from any surface anchoring. Since the material is anisotropic the orientation of the n-director in turn influences the magnitude of the dielectrophoresis forces and the rate of viscous flow and spreading. We have investigated the coupling between these effects during the spreading and actuation of nematic liquid crystal materials. A number of model geometries have been developed and used that allow key simplifications to be made in the theoretical analysis, which includes co- planar electrode arrangements. We acknowledge funding from the UK EPSRC (EP/J009865/1 and EP/J009873/1) and Merck Chemicals Ltd.

References: [1] T.B. Jones, Hydrostatics and steady dynamics of spatially varying electromechanical flow structures, J. Appl. Phys. 45, 1487–1491 (1974). [2] S. Xu, H. Ren, and S-T. Wu, Topical Review Dielectrophoretically tunable optofluidic devices, J. Phys. D: Appl. Phys. 46, 483001–483014 (2013). [3] C.V. Brown, G.G. Wells, M.I. Newton, and G. McHale, Voltage-programmable liquid optical interface, Nature Photonics 3, 403–405 (2009).

______* presenting author; E-mail: [email protected]

T 17 Bleaching wave dynamics in photobending Chen Xuana,b, and Mark Warnera aCavendish Laboratory, JJ Thomson Avenue Road, Cambridge, CB3 0HE, United Kingdom bDepartment of Mechanics and Engineering Science, Fudan University, Shanghai 200433, China

Yu et al0 show curling of photochromic polydomain liquid crystal networks (LCNs) illuminated by polarized ultraviolet (PUV). LCN sheets overshoot in that they curl until their edges reach an angle much bigger than 90 degrees and they self-eclipse.

Photoisomerization gives macroscopic contraction from the destruction of orientational order by bending the photosensitive guest molecules. We consider the dynamics of the rod-like trans population converting to a bent cis population together with non-Beer light absorption0 . We take the local incident light intensity to be the component of the Poynting flux normal to the locally- illuminated surface, i.e. cosϴ of light intensity from the source, where ϴ is the local tilt angle of the sample. The gradient of contraction in the sample makes it bend towards the light. The tilt angle ϴ is a function of both the cis fraction and incident light intensity, integrated along the sheet as accumulated curvature gives the tilt. A local cis fraction is triggered by the local light intensity, which depends on the local tilt ϴ. So the photoisomerization and the photobending are coupled both nonlinearly and non-locally.

The tilt in the photo-stationary state never reaches 90 degrees – there is no photo-stationary overshoot. But it is significant that maximal curvature need not be where the light intensity falls maximally, i.e. not in horizontal portions of the sheet. There is an incident light intensity for maximum bending, since the bending curvature is a non-monotonic function of light intensity, both statically and dynamically.

Our bending dynamics does overshoot: If light intensity is greater than that for maximum bending, the curvature is a non-monotonic function both of the sample arc lengths and time. One could expect a maximum curvature in the middle of the total sample arc length, at which cosϴ weakens the light intensity towards the threshold value. This explains why overshoots only occurs beyond certain light intensities and specimen lengths. After overshoot appears, the maximum curvature can grow, despite eclipsing, and then attenuates in time since the cis population begins to decay in dark regions and in those highly oblique to the incident beam. Through possibly several wobbles, overshoot vanishes and samples approach the equilibrium shape. This complex phenomenon shows bleaching waves play a crucial role in dynamical photobending and hence in future photo- mechanical actuation.

References 1. Yu Y, Nakano M, Ikeda T. Nature, 2003, 425(6954): 145-145. 2. Corbett D, Warner M. Physical review letters, 2007, 99(17): 174302.

T 18 Graphene based electrodes for electrically switchable liquid crystal contact lenses S. Kaura,b , D. Mistrya, H. Miltona, I. M. Syeda,c, J. Baileya, Y. J. Kima, K. S. Novoselova, C. J. Jonesa,b, P. B. Morgand and H. F. Gleesona,b aSchool of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom bPresent address: School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom cSchool of Physics and Astronomy, University of Dhaka, Dhaka, 1000, Bangladesh dEurolens Research, University of Manchester, Manchester, M13 9PL, UK

For decades, liquid crystals have enhanced our lives with numerous display and non-display applications which continue to grow to encompass innovations in other disciplines. The work presented in this paper represents one such amalgamation of liquid crystal science with another wonder material, graphene. At the University of Manchester, we have recently developed electrically switchable liquid crystal contact lenses to correct Presbyopia, the age related deterioration of the eye that affects everyone over the age of 50.1,2 Recently, we have further developed this technology to successfully replace the standard electrode material, Indium tin oxide (ITO) with electrodes made of graphene in the contact lenses.3 Transparent electrodes such as ITO are a necessary part of the electrically switchable liquid crystal contact lenses as they are for numerous photonic devices. The high global demand for ITO electrodes results in high manufacturing costs. In addition, ITO films are brittle and therefore unsuitable for flexible electronics such as paper-like displays, and ITO deposition is problematic for use in curved geometries such as the wearable contact lenses, which is our field of interest. Therefore, alternative electrode materials can simplify and speed up contact lens construction processes, and can be expanded to many other visual and numerical display applications. Previous work has successfully demonstrated that graphene is an excellent choice for electrodes in liquid crystal devices, with uniform switching and high optical transparency.4 In this work, we demonstrate that graphene can successfully be deposited onto PMMA substrates to form electrically switchable liquid crystalline contact lenses. The designed lenses are planar aligned and capable of providing a continuous increase in optical power of up to +0.7± 0.25 D when electrically switched. The lenses exhibit excellent optical contrast, demonstrated using polarisation microscopy and the measurement of point spread functions. The work demonstrates that the transparency, flexibility, electrical conductivity and adhesion to the substrates makes graphene an excellent choice for use in applications such as smart contact lenses. References 1 H. E. Milton, H. F. Gleeson, P. B. Morgan, J. W. Goodby, S. Cowling, J. H. Clamp, Proceedings of SPIE (2014), 9004, 90040H. 2 H. E. Milton, P. B. Morgan, J. H. Clamp, H. F. Gleeson, Optics Express (2014), 22(7), 8035. 3 S. Kaur, et al., To be sent to Nano Letters (2015). 4 P. Blake, et al., Nano Letters, (2008), 8 (6), 1704.

T 19 The investigation of mixtures of functionalized azocines – can LC phase behaviour be promoted by irradiation?

J. Hussey, G. H. Mehl 1Department of Chemistry, University of Hull, HU6 7RX, UK

The photochromic behavior of azobenzenes is typically characterized by light induced cis-trans isomerisations of the azo groups when irradiated with UV light. For such materials the trans form tends to be the more stable isomer. Hence when azobenzene groups are incorporated into rod– shaped molecules which can be mixed with liquid crystals or show liquid crystalline phase behavior, irradiation results in a reduction of the stability or complete loss of the LC phase, as the less linear cis isomer is formed. The investigation of materials which show photochromic properties, when irradiated is however increasingly interesting [1] hence it is attractive to investigate systems where LC is promoted on exposure to light. For azobenzene based systems, which form the largest pcalss of reported photochromic groups this has so far not been possible. The azocine moiety, shown in Figure 1, through known for more than hundred years, has only recently been found to show photochromism [2,3]. This class of materials is highly bent, due to the hydrocarbon linkage and thus the cis-conformer forms the more stable ground state isomer. It has been reported that on irradiation a more rod shaped trans isomer is formed. [3-5] The chemistry of the azocine group has not yet been investigated much, thus it was the aim to explore this. In this contribution we report on the results of the efforts of an improved synthesis of diazocine core, our results of functionalizing this core with mesogenic groups “R”, the chemical and photochromic characterisation of these systems and we will compare these results with those reported earlier [3-5]. We will report on the results of the investigation of the LC properties of these systems as neat substances and in mixtures with suitable liquid crystals hosts and the effects on nematic phase stability on irradiation with light and will structure properties correlations will be disucssed.

.

Figure 1: Azocine moiety

[1] T. Kosa, L. Sukhomlinova. L.L. Su, B. Taheri, T.J. White, T.J. Bunning, Nature, 2012, 485, 347-349. [2] H. Duval, Bull Soc.Chim. Fr. 1910, 7, 727-732 [3] R. Siewertsen, H. Neumann, B. Buchheim-Stehn, R. Herges, C. Nather, F. Renth, F. Temps, J. Am. Chem. Soc. 2009, 131, 15594-15595. [4] H Sell, C. Naether, R. Herges, Beilstein J. Org. Chem. 2013, 9, 1–7. [5] S. Samanta, C. Qin, A. J. Lough, G. A. Woolley, Angew. Chem Int Ed. 2012, 51, 6452 –6455.

T 20 Improving the optical performance of liquid crystal contact lenses by implementing axial alignment

J. Baileya,b, S. Kaura,b, D. Mistrya, H. F. Gleesona,b and J.C. Jonesa,b. aSchool of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom bPresent address: School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom

Presbyopia is an age related disorder which affects everyone over the age of 50 due to natural deterioration of the eye. Contact lenses which have a switchable focus are currently being investigated to assist people who do not want to wear glasses, but need correction for both far and near vision. Liquid crystal contact lenses offer a solution to this problem as their refractive indices are controllable by applying an electric field across the device 1-3. Using a liquid crystal with a larger bi-refringence results in a lens with a bigger focal power range. However, it has been preivously shown by Milton et. al. that applying a field just above the Fréedericksz transition results in significant scattering when using a higher bi-refringence liquid crystal 1,2. This paper discusses techniques which can be used to reduce the scattering when using a high bi-refringence liquid crystal. Scattering in the lens occurs from the circular asperities on the PMMA contact lens substrates interrupting the alignment of the liquid crystal. These asperities occur from the laithing manufacturing process used to construct contact lenses. Polishing the lenses to remove these asperities is possible, but it is both time consuming and expensive. Instead, defects over the lens were reduced by implimenting axial alignment, which followed the direction of the circular asperity pattern. This was achieved by rubbing directly into the pedot electrode layers. Axial alignment reduced scattering when switching the lens just above the Fréedericksz transition, which lead to an improved optical performance. Reduced scattering enables the use of liquid crystals with a higher bi-refringence. Our experiments, which used E7 as the intermediate liquide crystal layer, resulted in a larger switching power (3.5 ± 0.5 D) than seen in similar liquid crystal contact lenses 1-3.

References 1 H. E. Milton, H. F. Gleeson, P. B. Morgan, J. W. Goodby, S. Cowling, J. H. Clamp, Proceedings of SPIE (2014), 9004, 90040H. 2 H. E. Milton, P. B. Morgan, H. F. Gleeson, J. H. Clamp, Optics Express (2014), 22(7), 8035. 3 S. Kaur, H. Milton, D. Mistry, I. M. Syed, J. Bailey, K. S. Novoselov, A. K. Geim, J. C. Jones and H. F. Gleeson, Nano Letters (2015).

T 21 Acousto-optics in dispersed LC systems for applications in ultrasonics Oksana Trushkevych, Tobias J. R. Eriksson, Silvaram N. Ramadas and Rachel S. Edwards Department of Physics, University of Warwick ,Coventry, CV4 4AL, UK

Acousto-optic effects have been previously investigated in aligned LCs as they hold promise for visualisation of acoustic fields [1-4]. Acousto-optic sensors based on homeotropic cells 200 μm thick were developed commercially for use at oblique incidence in water tanks [5,6]. These visualise acoustic field, but have the limitations expected from thick nematic films and suboptimal geometry. Recently, acoustic clearing of a PDLC film by surface acoustic waves at high frequency has been reported [7]. This paper presents developments toward using PDLC films as ultrasound sensors. We demonstrate acousto-optic effects in PDLC films using longitudinal ultrasound at frequencies commonly used in applications in non-destructive testing and medicine. Longitudinal waves at frequencies of 1 MHz and 2 MHz are used to achieve acoustic clearing of PDLC films placed directly on the ultrasound- generating transducers. Heating effects are carefully monitored using thermal imaging, and are found not to be the main cause of PDLC clearing.

a) b) c) Figure1. a) PDLC film on top of a plate which is vibrating at 730 kHz (12:0 centrosymmetric mode) showing clearing in the central area ~2mm in diameter; b), c) plate displacement amplitude measured using laser vibrometry. The area of the strongest displacement is 1.9mm in diameter and correlates well with the PDLC result. The PDLC films are also shown to be able to image vibration of plates. The regions of the plates with the largest displacement are visualised using PDLC with good resolution, with the displacements confirmed using laser vibrometry. The vibrational properties of the plate are not influenced significantly by the addition of the sensing film. The possibility of such imaging shows promise for a variety of applications including fast characterisation of gas-coupled transducers for applications such as gas-flow measurement. Overall, these first steps and demonstrated effects suggest that acousto-optic effects in disperse LC systems and developing PDLC films for ultrasound sensing is highly promising for applications in ultrasonic sensing, particularly in non- destructive testing.

Acknowledgements: the authors would like to thank the University of Warwick Energy GRP for the Research Award that funded this research, Merck for providing materials, and Dr. A. Dyadyusha, Cambridge University, for valuable advice on PDLC.

References 1 O.A. Kapustina, Acoustical Physics, (2008), 54, 2, 180–196 2. J. V. Selinger et al, Phys. Rev. E (2002) 66, 051708 3. A. P. Malanoski et al, Phys. Rev. E (2004) 69, 021705 4. V. A. Greanya et al, Liquid Crystals (2005) 32, 7, p933-941 5 J.S. Sandhu et al, Advances in Acoustics and Vibration, (2012), 275858; 6 G.L. Rodriguez et al, Ultrasonics,(2011) 51, 847 7 Y.J. Liu et al, Adv. Mat, (2011) 23, 1656

P 1 Turbulent Textures - Art with Liquid Crystals Ingo Dierking School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK

Textures of liquid crystals, observed in the polarized light of a microscope, can already by themselves be considered as nature's little pieces of art. Due to their birefringence and varying optical path differences, brightly varying textures can be observed easily. Defects at visible length scales, due to the very small elastic constants, and repetitive patterns formed from the self- organized superstructures contribute to the aesthetic appeal of optical liquid crystal textures.

Figure 1: Image produced from (a) a smectic fan-shaped texture, (b) a nematic texture with point defects, (c) a Twist Grain Boundary phase, and (d) a nematic Schlieren texture.

The modern opportunities of digital image manipulation allow for an easy and creative way to change the appearance of texture pictures, giving them possibly even more aesthetic appeal than the already beautiful original research images. Certainly, they are reminiscent of many modern art paintings found in galleries all over the world.

P 2 Using DPD Simulation to Study Phase Behaviour of Liquid Crystal-

Gold Nanoparticle Composite Materials. Sarah Gray* and Mark R. Wilson Department of Chemistry, Durham University, Durham, DH1 3LE, UK

It has been suggested, from experimental results1,2, that self-assembling 3-dimensional ordered arrays of gold nanoparticles are produced with the aid of liquid crystal ligands. These materials could see application to a huge range of areas (photonics, electronics, optics) if the nanoparticle structure was readily manipulated.

The typical molecular structure in these experiments is of nematic-phase forming calamitic mesogens, laterally attached via a short alkyl thiol chain to relatively small (<10 nm) spherical gold nanoparticles – the illustration above gives specific details for the materials studied in reference [2].

This study uses Dissipative Particle Dynamics (DPD) simulations to evaluate potential mechanisms involved in the self-assembly process, and to gain understanding of the factors that govern the phases produced. To the right is an illustration of suggested structures produced by a range of variations on the molecular structure (description given above)1. By simulating these “supermolecules” at a molecular level, we can either validate these proposed structures, or put forward an alternative “picture” of how alignment occurs.

We study a variety of different molecular architectures, as well as the impact of anisotropic solvent and shearing, in an attempt to comprehensively describe the phase behaviour of these materials. For instance, little mention is given to the potential content of free liquid crystal molecules in these materials experimentally, but we find that the amount of anisotropic solvent present has a significant impact

on the order parameter S2 of the bonded mesogens (illustrated left), and as such has the potential to influence the proposed self-organisation process.

1X. Mang, X. Zeng, B. Tang, F. Liu, G. Ungar, R. Zhang, L. Cseh and G.H. Mehl, J. Mater. Chem. (2012) 22:11101-11106. 2L. Cseh and G.H. Mehl, J. Am. Chem. Soc. (2006) 128:13376-13377

* presenting author, email: [email protected]

P 3 All Optical Switching of Nematic Liquid Crystal Films Driven by Localized Surface Plasmons

Linda S Hirst

Department of Physics, University of California, Merced, USA

We demonstrate an all-optical technique for reversible in-plane and out-of-plane switching of nematic liquid crystal molecules. Our method leverages highly localized electric fields (“hot spots”) and plasmonic heating generated in the near-field region of densely packed gold nanoparticle layers. These nanoparticles can be optically excited on-resonance at low power and optical wavelengths. Using polarized microscopy and transmission measurements, we observe temperature dependent switching from homeotropic to planar with an on-resonance excitation intensity of less than 0.03 W/cm2 and no external applied electric field. In addition, we controllably vary the in- plane directionality of the liquid crystal molecules in the planar state by altering the linear polarization of the incident excitation. Using discrete dipole simulations and control measurements, we demonstrate the spectral selectivity of our device in this new photonic application.

1M.T. Quint, S. Delgado, Z.S. Nuno, L.S. Hirst and S. Ghosh, Optics Express 23, 5, 6888 (2015).

P 4 High-Speed Microscope Imaging of Liquid Crystal Dynamics C. Burkea, D. Emerson b, Y. Jinc, J. Guastoc, J. H. Adler b, T. J. Athertona aDepartment of Physics and Astronomy, Tufts University, Medford, MA 02155 b Department of Mathematics, Tufts University, Medford, MA 02155 cDepartment of Mechanical Engineering, Tufts University, Medford, MA 02155

Microscopy has long been a key tool in the study of LCs: Polarizing Optical Microscopy (POM) is a powerful technique for identifying LC phases based on textures that can also be used for quantitative imaging. A key breakthrough in the field has been the use of 3D imaging techniques, such as Fluorescence Confocal Microscopy (FCPM)5 and Confocal Anti-Stokes Raman (CARS)6 microscopy. These powerful techniques enrich our understanding of domain wall structure and defect topology, however, they are limited to static LC studies and lack the temporal resolution to capture dynamic rearrangement. Indeed, few techniques are available to study dynamic phenomena in LCs. The Convergent Beam method7 captures LC director information with sub-millisecond resolution by observing the time variation of guided modes through a sample but lacks spatial resolution. Attaching a video camera as the imaging device to POM is one possibility, and has allowed studies of many phenomena including LC-mediated self-assembly of colloids and defect dynamics. Unfortunately, the imaging is limited to about 60 fps. 3D video imaging at similar framerates is possible with confocal microscopy using Nipkow disks or fast-scanning galvanic mirrors8. Nonetheless, there is no existing technique that offers both the spatial and temporal resolution necessary to study LC dynamics. Recently, we have begun to create such a technique by combining high speed imaging with Polarizing Microscopy. To gain additional insights, the experiments have proceeded in close collaboration with multigrid nematodynamics simulations and optical modeling. This study presents some initial results for a Freedericksz cell as a validation exercise, as well as an In-Plane switching device.

5 O. D. Lavrentovich, “Fluorescence confocal polarizing microscopy: Three-dimensional imaging of the director”, Pramana, 61 373-384 (2003) 6 E. A. Büyüktanir, K. Zhang, A. Gericke and J. L. West, “Raman Imaging of Nematic and Smectic Liquid Crystals”, Molecular Crystals and Liquid Crystals, 481 39-51 (2008) 7 L. Z. Ruan and J. R. Sambles, “Dynamics of a twisted nematic cell using a convergent beam system”, Journal of Applied Physics, 92, 4857 (2002) 8 O. D. Lavrentovich, “Confocal Fluorescence Microscopy”, chapter in “Optical Imaging and Spectroscopy”, John Wiley & Sons (2003)

P 5 Synthesis and Properties of Novel Liquid Crystals with Bulky Terminal Groups Designed for Bookshelf Geometry Ferroelectric Mixtures

Rami Pasha and Michael Hird

Department of Chemistry, University of Hull, Hull, HU6 7RX [email protected]

This research programme will be concerned generally with the ferroelectric liquid crystals for microdisplay applications. Ferroelectric liquid crystal displays switch 1000 times faster than conventional liquid crystal displays, and offer much higher resolution, and hence are suitable for microdisplay applications. Novel liquid crystals will be synthesized, with the broad aims of enhancing switching speeds and improving the alignment of the molecules in the display. All the final products will be evaluated for their mesomorphic properties and a wide range of other physical properties, and the most suitable compounds will be formulated into mixtures for evaluation in prototype microdisplays. Difluoroterphenyls1 are well-recognised as excellent host materials for low viscosity, fast-switching ferroelectric mixtures. Ferroelectric liquid crystal displays switch faster than conventional liquid crystal displays, and offer much higher resolution, and hence are suitable for microdisplay applications2.

The synthesis and mesomorphic properties of a systematic range of ortho difluoroterphenyls and ortho difluoroquartetphenyls with bulky terminal chains are detailed. The bulky terminal chain consists of a methoxy-4,4-dimethylpentyl group, a trimethylsilyl unit and a dimethylethyl group. All the final products will be evaluated for their mesomorphic properties and a wide range of other physical properties, and the most suitable compounds will be formulated into mixtures for evaluation in prototype microdisplays. The compounds give a nematic phase however, all the compounds give a SmC phase.

1- G. W. Gray, M. Hird, D. Lacey and K. J. Toyne, J. Chem. Soc., Perkin Trans. 2, 1989, 2041. 2- M. Walba, D.J. Dyer, X.H Chen, U. Muller, P Cobber, R. Shao, and N.A Clark, Molecular Crystal and Liquid Crystal 1996, 288,83.

P 6 Homeotropic alignment in switchable optical power, liquid crystal contact lenses. D. Mistrya, I. M. Syeda,c, S. Kaura,b , H. Miltona, J.Baileya,b, J.C. Jonesa,b, P. B. Morgand, J. H. Clampe and H. F. Gleesona,b aSchool of Physics and Astronomy, University of Manchester, Manchester, M13 9PL, United Kingdom bPresent address: School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, United Kingdom cUniversity of Dhaka, Dhaka, 1000, Bangladesh dEurolens Research, University of Manchester, Manchester, M13 9PL, UK eUltravision CLPL, Leighton Buzzard, LU7 4RW, UK

A liquid crystal contact lens based on homeotropic device geometry with a switchable optical power has been constructed1. This builds on previous work on homogenously aligned lenses2. Such devices have promising ophthalmic applications for effective treatment of presbyopia, an age- related disease of the eye affecting nearly 100% of the population by middle age. Presbyopia is a stiffening of the accommodating (“auto-focus”) lens of the eye meaning it cannot focus on objects as close to it as a young eye can. The contact lens contains the negative dielectric liquid crystal MLC-20813. Switching this material gives the lens a continuously variable optical power of up to 2.00 ± 0.25 퐷. The maximum change in power is achieved with an applied voltage of 7.1 푉푟푚푠. This variable additional change in optical power makes the device an ideal treatment for presbyopia as the user can turn on the extra optical power when they are performing near visual tasks, as and when required. Using a homeotropic instead of homogeneous geometry in a contact lens has several advantages:  The lens’ unpowered state is polarisation-independent so produces a higher quality image compared to a birefringent state. This means a low-powered device can be designed with optimal distance vision which is more crucial and used more frequently than near vision;  The lens construction becomes easier as only one surface needs to be rubbed. This was chosen to be the concave surface which is much easier to rub uniformly;  The two lens substrates do not need to be aligned with respect to one another thus simplifying construction. Acknowledgements I.S. thanks the UK Department for International Development (DFID). D.M. thanks the EPSRC and UltraVision CLPL. The authors would like to thank Prof. John Goodby and Dr. Stephen Cowling. References 1 I. Syed, S. Kaur, H. E. Milton, D. Mistry, J. Bailey, J. C. Jones, P. B. Morgan, J. H. Clamp, H. F. Gleeson Submitted to Applied Optics 2015 2 H. E. Milton, P. B. Morgan, J. H. Clamp, H. F. Gleeson Optics Express (2014), 22(7), 8035. 3 Merck Chemicals Ltd. Physical properties of MLC-2081are quoted in the Merck Data Sheet.

P 7 The dynamic response of nematic devices with an unconventional geometry.

Marianna Minarova,a Shajeth Srigengen,a Cliff Jonesa,b and Helen F. Gleesona,b

aSchool of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK bSchool of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

Nematic liquid crystals are increasingly used for non-display applications such as sensors or electro-optic devices and interconnects. One such area that is attracting increasing attention is the use of liquid crystals in switchable contact lenses for the correction of presbyopia (the need for reading glasses in the over-50s)9, 10. The contact lens geometry requires a layer of liquid crystal enclosed by substrates of differing curvatures, such that the device thickness varies as a function of radial distance in the lens (see figure). In the lens, the change in refractive index of the nematic liquid crystal layer that occurs on application of a voltage above the threshold voltage causes a change in the focal length of the lens. Optical zone

LC layer 50 μm Mating surface 67 μm Upper substrate Lower substrate Lower substrate

The switching of the liquid crystal contact lens is more complicated than in conventional devices with parallel substrates. The threshold voltage (Vth) and response time (τon) of a planar nematic layer are:

2 k11 ηd Vth = π√ , τon = 2 2, ε0Δε ε0ΔεV − k11π where k11 is the splay elastic constant and Δε is the dielectric anisotropy of the material. The response time of the liquid crystal layer is clearly strongly dependent on the thickness. We report a detailed study of the electro-optic response of a nematic liquid crystal layer of non-uniform thickness. The response of a parallel-aligned wedge cell designed to model the liquid crystal layer in the contact lens is described and compared with parallel devices of different thicknesses. The study gives an insight into the dynamics of liquid crystal based lenses and offers an understanding of some of the electro-optic effects reported to date1,2.

9 H. E. Milton, H. F. Gleeson, P. B. Morgan, J. W. Goodby, S. Cowling and J. H. Clamp, ‘Switchable liquid crystal contact lenses; dynamic vision for the ageing eye,’ Proc. of SPIE Vol. 9004 90040H-1-6 (2014) 10 H.E. Milton, P.B. Morgan, H. F. Gleeson and J. H. Clamp, ‘Design and operation of PMMA-based liquid crystal lenses for contact lens use,’ Optics Express, 22(7) 8035040 (2014)

P 8

Measuring the temperature dependence of the anisotropic viscosity of nematic liquid crystals using laser tweezer techniques

David L. Weia, Mark R. Dickinsona, James Baileyb, Cliff Jonesa,b and Helen F. Gleesona,b,

a School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK b School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

The dynamic response characteristics of a liquid crystal (LC) device are dependent upon its viscosity coefficients and dielectric anisotropy. Optimisation of these properties allows for LC devices with faster response times. With such a wide variety of LC materials, information regarding the viscous properties is often incomplete. The effect of external stimuli, including temperature and electric fields, on these properties provides valuable information for device behaviour. Laser tweezers provide alternate routes to determine this information, as the dimensions are well suited to these techniques.

Manipulation of micron-sized particles with optical tweezers provides a unique method for LC systems to be studied. Dispersed colloidal particles can be trapped and used to probe the fundamental properties of these systems, particularly anisotropic viscosity coefficients in the low Ericksen regime. These properties can be explored under a variety of external conditions, and with different tweezing techniques such as viscous drag measurements or particle tracking.

Optical tweezers also allow the forces acting on colloidal particles in these systems to be explored. The response of trapped particles can provide insight into the behaviour and motion of particles in such systems. The influence of anisotropic LC properties, and of external stimuli, on this behaviour can be studied for a wide variety of materials.

Cells fabricated with PEDOT:PSS are also investigated as an alternative to ITO, which is shown to impose limitations on such measurements.

Acknowledgements

The author would like to thank the EPSRC and Merck Chemicals Ltd.

P 9 Molecular Dynamics Simulation of Fibre Formation

Alireza Dastan and Doug Cleaver

Materials and Engineering Research Institute, Sheffield Hallam University, Howard Street, Sheffield, S1 1WB, UK

In this poster, fibre self-assembly, which is a very common phenomenon in a range of areas, was investigated through molecular dynamics simulation of a mixture of spherical (solvent) and discotic particles. Using the Coarse-Grained method, the interaction between discotic particles is governed by the well-known Gay-Berne potential, while the spherical particles interact with each other through Lennard-Jones potential. Three different shape parameters for discotic particles (length to breath ratio) and also three anisotropy values in their potential energy were considered in this study and the effects of these parameters on the fibre self-assembly were studied. Results showed that the self-assembly of fibres is a hierarchical process. It means that, at the first step of this process, many threads of 4-6 face-to-face oriented discotic particles form and then some of them attach laterally and make a cluster. This cluster grows both laterally and longitudinally and forms the final fibre. It was observed that the process of fibre self-assembly is a function of temperature. That is, only in a narrow-range of temperature, a defect-free fibre forms and below this range, the self-assembled structure is a defected one. The outcome of this study can shed light on our understanding of the fibre formation process and also shows some of important parameters affecting the final structure. The results may possibly be used in the control of fibre self-assembly.

P 10

Polarized Raman Spectroscopy Measurements of Liquid Crystal Order Parameters

Zhaopeng Zhang, Helen F Gleeson

School of Physics and Astronomy University of Manchester, Manchester, M13 9PL

Polarized Raman Spectroscopy (PRS) is one of the experimental methods which can be employed to deduce orientational order parameters in liquid crystals. Previous studies have produced values of 1,2 the measurement of P200 that are in excellent agreement with theory and relatively recently it has 3 also been demonstrated that reliable measurements of P400 can be obtained . However, a key assumption of the methods used is that the vibrational direction for selected Raman-active mode is coincident with the molecular long axis. We have relaxed this assumption, allowing a small tilt angle 훽0 between the vibration direction and the molecular main axis. Our results indicate a strong effect on the depolarisation ratio value when 훽 0 is non-zero, increasing as 훽 0 is increased. Consequently, the order parameters deduced from fits to the experimentally determined depolarization ratio are different depending on whether or not 훽0 is included.

It has also long been known that the order parameters deduced from PRS using different vibration modes are found to be different within the same sample. As a result, only certain vibration modes can be reliably selected for analysis, limiting the application of PRS. We have investigated this issue and a reasonable explanation has been given by introducing a different dipole symmetry model, specifically we assume that the phenyl stretching mode has cylindrical symmetry while the cyano stretching mode has elliptic cylindrical symmetry. By accounting for this different symmetry model, it is possible to get exactly the same set of order parameters from both phenyl and cyano stretching modes. However, the introduction of additional fitting parameters does not necessarily offer a robust fitting method to deduce order parameters using this concept.

References

1 S. Jen, N. A. Clark, P. S. Pershan, and E. B. Priestley, J. Chem. Phys. (1977),66, 4635 2 W. J. Jones, D. K. Thomas, D. W. Thomas, and G. Williams, J. Mol. Struct. (2004), 708, 145.

3 C. D. Southern and H. F. Gleeson, Eur. Phys. J. E (2007), 24, 119.

P 11 Novel Resists for Nanofabrication on Insulating Substrates

Karolis Virzbickasa, Farhan Hasana, Greg O’Callaghanb, Dennis Zhaob, Jon A. Preeceb and Alex P. G. Robinsona

aSchool of Chemical Engineering, University of Birmingham, UK bSchool of Chemistry , University of Birmingham, UK

Electron beam lithography is widely used in high value low volume manufacturing, and in research, of nanoscale electronics and micromechanical systems and nanotechnology. However, it is not possible to directly pattern poorly conductive or insulating substrates with feature sizes smaller than about 100 nm due to charging by the electrons. A number of existing strategies such as the use of charge dissipation layers or patterning of intermediate moulds have been investigated but typically add complexity and cost without necessarily significantly improving the situation. In this project, we investigate and develop photoresists using Triphenylene organic conductors to incorporate the charge dissipation strategy directly into the lithographic imaging layer. We characterise the conductivity, lithographic, etching and other properties of the new resists and investigate their performance for nanoscale patterning of substrates such as glass and gallium nitride.

P 12 Structure and organisation in chromonic phases: MD simulation study of Azo dyes in aqueous solution Chami Fa and Wilson Ma aDepartment of Chemistry, Durham University, Durham, DH1 3LE, UK

Chromonic liquid crystals occur widely in aqueous dispersions of many formulated products such as pharmaceuticals and the dyes used in inkjet printing. They are also used in material science for fabricating highly ordered thin films and anisotropic carbons. Chromonic mesophases are usually formed in water from disk-like or plate-like molecules1. At low concentrations aggregates are formed in solution; but when the volume fraction is sufficiently high, liquid crystals occur. The azo dye Acid red 266 known as Nylomine, is a disparate ionic dye that forms chromonic mesophases at unusually low concentrations (0.25\% (w/w)). It has a chemical structure that is similar to that of ESY (Fig.1b) , but its behaviour is very different. Nylomine exhibits a nematic tiger-skin texture at 1\% (w/w) and does not show a sharp N/M transition. Despite the low concentration, Nylomine aggregates have a cross area far larger than the molecular area2-4. In an attempt to gain insight on aggregation and structure of this chromonic mesophase, we carried out molecular dynamics simulation in water at 6 % (w/w) on a large system with four different starting configurations. The binding energy of Nylomine dimer was estimated from steered MD simulation and from the potential of mean force. can the building unit in Nylomine be much larger species than dimer or is the probability of branching in stacks.

CF3 NH2 O H N Cl N SO3Na N N

OH

NaO S NaO S 3 3 (a) Acid red 266 dye (Nylomine) (b) Sunset Yellow dye (Edicol )

Fig.1 Chemical structure of azo dyes

References 1. John Lydon, Handbook of Liquid Crystals Volume 6. Nanostructured and Amphiphilic Liquid Crystals (2014). 2. Bernd Neumann, Klaus Huber and Peter Pollmann, Phys. Chem. Chem. Phys. (2000), 2, 3687. 3. Bernd Neumann, Langmuir (2001), 17, 2675. 4. J. W. Jones, Helen Wheatcroft, A. P. Ormerod, Abdullatif Alfutimie, Douglas J Edwards and G. J. T. Tiddy, in press

P 13 AFM study of supermolecular dendritic liquid quasicrystals R. B. Zhang,a X. B. Zeng,a V. Percec b and G. Ungara,c a Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK b Department of chemistry, University of Pennsylvania, Philadelphia, Pennsylvania, USA c Department of Physics, Zhejiang Sci-Tech University, Hangzhou, China

The self-assembling dendron can from cones which further assemble into supramolecular spheres. These spheres can then generate spherical phases with 3D periodicity. The large majority of such 1 2 periodic 3D structures show Pm3̅n or P42/mnm . Symmetries. They are featured by alternating densely and sparsely populated layers of spheres. One way of representing these structures is to view them as tilings that cover an infinite plane using only squares and equilateral triangles3. Each tile is a column containing individual micelles, having periodicity along c. Only three kinds of tiles, one square and two triangular, are needed to construct these structures. A sparse layer of the Pm3̅n 4 represents a simple square 4 tiling, while that of the tetragonal P42/mnm phase has the ubiquitous 32434 Arhimedean tiling. The presence of the 32434 tiling was the first hint of a dodecagonal quasiperiodic phase in supramolecular spherical dendrimers. In 2000 the first liquid quasicrystal (LQC) formed by a dendron was discovered by our group using synchrotron X-ray diffraction two decades after Shechtman’s seminal discovery of LQCs in metals. The recorded diffraction pattern from a single domain showed a crystallographically forbidden 12-fold rotational symmetry4. Using quasiperiodic tiling, the same elements (square and triangle) can be used to construct models of the LQC. However, in the real LQC the micelles would also be somewhat away from the ideal positions assumed by our starting model. Here we studied the LQC tiling using atomic force microscopy.

Spheres on sparse net at z=1/4, 3/4

z=1/2

Spheres at z=0, 1

Decorated sparse net

References 1. S. D. Hudson. et al., Science, (1997), 278, 449. 2. G. Ungar. et al., Science, (2003), 299,1208. 3. X. B. Zeng, G. Ungar, philosophical magazine, (2006), 86, 1093. 4. X. B. Zeng. et al, Nature, (2004), 428, 157.

P 14 Hexagonal Close Pack Structures in Thermotropic Liquid Crystals M. H. Yena, J. Chaiprapaa, X. Zenga, L Csehb, G. H. Mehlb, and G. Ungara aDepartment of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK bDepartment of Chemistry, University of Hull, Hull, HU6 7RX, UK

Wedge-shaped dendron-based mesogens can form columnar or spherical supramolecular assemblies. The spherical “micellar” aggregates self-assemble into 3-D cubic phases. However, until now no close-packed structures have been reported in thermotropic LCs, either face-centred cubic (FCC) or hexagonal close packing (HCP). This is due to the inaccessibility of the octahedral interstices in the close pack structures to the flexible chains of the micellar corona. In our study, a close pack structure was observed in the minidendron-alkane blends. We found that in a mixture of sodium 3,4,5-tridedocyloxybenzoate salts (12-12-12Na) with 15% n-C19H40, the HCP phase is obtained. Similar situation was also observed in rubidium 3,4,5- tridedocyloxybenzoate salts (12-12-12Rb). We suggest that the role of the added alkane is to fill the octahedral interstices in the HCP. We then replace n-C19H40 by n-C19D40. The deuterated alkane can be distinguished by neutron scattering from the alkyl tails of the minidendrons. The position of the added alkane thus can be located. The electron or scattering length density maps can be reconstructed from the diffraction patterns. Figure 1 (a) shows the top view of the electron density (ED) map in the HCP phase. The low ED region is located at the octahedral interstices. Interestingly, in the neutron scattering length density (NSLD) maps shown in Figure 1 (b), it is the high NLSD that is located at the octahedral interstices. Thus deuterated alkane fills the material-deficient octahedral vacancies and stabilizes the close pack structure. This is the first time the close pack structure is reported in thermotrpic liquid crystals. This work also demonstrates the power of combined X-ray and neutron diffraction in the study of LC self-assembly. (a) (c)

(b)

Figure 1 The top view of (a) ED map and (b) NSLD map; (c) ED and NLSD map in a HCP unit cell (green: high-ED; red: low-ED; blue: high-NSLD)

References G. Ungar, X. Zeng, Soft Matter (2005), 1, 95

P 15 Chessboard and Wigwam phases in X-Shaped Polyphiles Huanjun Lua, Feng Liua, b, Xiangbing Zenga, Goran Ungara, Hergold Ebertc and Carsten Tschierskec aDepartment of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK bState Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, China cInstitute of Organic Chemistry, Marten-Luther University, Halle, Germany

A variety of phase morphologies have been observed in X-shaped liquid-crystalline polyphilies1. Most prominent are a series of 2D honeycombs and novel 3D-ordered mesophases2, 3. The present X-shaped polyphilic molecule HEP14 is made up of a rigid rod-like aromatic core with an alkyl and a semiperfluorinated chain attached laterally to opposite sides of the aromatic moiety. This compound forms five phases on cooling from 180 ˚C to 100 ˚C. The first two high-temperature phases, p4mmHT and p4mmLT are both 2D columnar (plane group p4mm), while the lattice parameter changes from a = L (L = molecule length) to a = L√2. Combined with the reconstructed electron density map, this suggests that they are both square

honeycombs. In the p4mmHT phase all cells are the same with mixed alkyl and semiperfluorinated chains.

In the p4mmHT, alkyl and semiperfluorinated chains are partially separated in alternative chessboard cells. On cooling, the squares contract into rhombs, resulting in a rectangular honeycomb (p2mm phase). After that, a 2D-3D transition takes place with the reorientation of the aromatic rods. In the primitive tetragonal 3D phase (P4/mmm), the rods twist to form a cage-like “double wigwam” structure (see Figure) with the alkyls (red) inside and the fluorocarbon chains (blue) outside the cage. At still lower temperatures the p2mm rhombic honeycomb phase re-enters, this time with complete alkyl-fluoroalkyl microphase separation. This remarkable phase sequence is a consequence of the competition between tendencies for mixing, phase separation and space filling. To our knowledge the “wigwam” phase is the first example of a 3D LC honeycomb.

References 1. G. Ungar, C. Tschierske, V. Abetz, R. Holyst, M. A. Bates, F. Liu, M. Prehm, R. Kieffer, X. B. Zeng, M. Walker, B. Glettner, A. Zywocinski, Adv. Funct. Mater. (2011), 21, 1296. 2. B. Glettner, F. Liu, X. B. Zeng, M. Prehm, U. Baumeister, M. Walker, M. A. Bates, P. Boesecke, G. Ungar, C. Tschierske, Angew. Chem. Int. Ed. (2008), 47, 9063. 3. B. Chen, U. Baumeister, S. Diele, M.K. Das, X.B. Zeng, G. Ungar, C. Tschierske, J. Am. Chem. Soc. (2004), 126, 8608.

P 16 Novel mesomorphic behaviour of a chirally-doped liquid crystal dimer, exhibiting the twist-bend nematic phase.

Craig T. Archbolda*, Richard J. Mandlea, Edward J. Davisa, Stephen J. Cowling, John W. Goodbya

aDepartment of Chemistry, The University of York, York, YO10 5DD *[email protected]

In recent years, the twist-bend nematic (NTB) liquid crystal phase has been an area of particular interest because of its potential for use in devices. The focus thus far has been on the determination of its structure and properties.1-4 However, there has been little study into the effects of chiral dopants on the properties of materials displaying the NTB phase despite the prevalence of chiral liquid crystal phases in devices. This work was undertaken in the hope of furthering our understanding of the properties of materials that exhibit the NTB phase as well as their possible technological applications. We demonstrate the effects of doping a liquid crystalline material exhibiting an enantiotropic NTB phase (Compound 1) with two different chiral dopants (Compounds 2 and 3), the structures of which are given in Figure 1.

Figure 2: Structures of Compounds 1-3. Across a range of dopant weight percentages, several interesting properties were observed. These included a direct isotropic to NTB transition (Figure 2 (a)), showing for the first time the natural texture of the NTB phase rather than the paramorphotic texture observed on transition from the nematic phase; a previously unobserved, weakly birefringent phase, appearing only upon annealing slightly above the isotropic to NTB transition temperature (Figure 2 (b)); and the emergence of a particularly wide temperature (≈ 10 °C) Blue Phase III (BPIII) (Figure 2 (c)). These results demonstrate a clear effect on the properties of these materials upon introduction of a chiral dopant, however the NTB phase itself is largely unaffected when viewed on an untreated glass slide. a) b) c)

Compound 1: Compound 1: Compound 1: 90% 90% 95% Compound 3: Compound 3: Compound 2: 5% Figure10% 3: a) Direct isotropic to NTB10% transition at 80.3 °C b) Weakly birefringent phase observed upon annealing at 80.6 °C for 2 hours c) BPIII observed at 82.3 °C.

1. L. Beguin et al., Journal of Physical Chemistry B, 2012, 116, 7940-7951. 2. M. Cestari et al., Physical Review E, 2011, 84. 3. R. J. Mandle et a.l, Journal of Materials Chemistry C, 2014, 2, 556-566. 4. D. Chen et al., Proceedings of the National Academy of Sciences of the United States of America, 2013, 110, 15931-15936.

P 17 Investigation of the Electric Field-Induced Behaviour of Biaxial, Smectic Liquid Crystals using a Phase Sensitive Detection Method J. W. Fostera, J. Ish-Horowicza, V. P. Panova, M. Nagaraja and J.C. Jones*a,b a School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK b School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

The common nematic liquid crystal phase used in television and mobile-phone displays is uniaxial and has simple cylindrical symmetry. Applying an electric field reorients the long axis of the system causing the desired change in optical properties to make the optical contrast of the display. However, this is inherently a slow process. One approach to forming a much faster response is to use a biaxial phase, where the system is biaxial and has orthorhombic or mono-clinic symmetry. With such symmetries the material properties also differ along directions perpendicular to the conventional symmetry axis. Field-induced transitions have the potential to be far faster than in conventional uniaxial liquid crystals. The best characterised example is the ferroelectric Sm-C*, where the speed of the transition arises from the ferroelectric polarisation but the electro-optics are greatly affected by biaxiality [1].

We present the investigation of electric field-induced behaviour of a difluoro-terphenyl based liquid crystal- MH222 (2',3'-difluoro-4-heptyl-4"-nonyl-1,1':4',1"-terphenyl) in its Sm-A and Sm-C mesophases using a phase sensitive detection method. A home-built experimental set-up designed to measure dielectric permittivities at high electric fields [2] will be shown. The set-up is based on the principle of applying a sine wave test voltage to the liquid crystal device via a high voltage amplifier and deducing the impedance of the device from the complex voltages measured by a lock- in amplifier. Extensive calibration procedures were carried out using devices of various electrode geometries and a standard liquid crystal of well-known permittivity.

The general utility of the setup is demonstrated though the measurement of the temperature and electric field dependence of two permittivity components in the uniaxial nematic and Sm-A mesophases; and the calculation of the three permittivity components in the biaxial Sm-C mesophase of MH222 [3]. Also presented are the results of investigations into the elastic constant of the material and the anchoring energy of the experimental cells used. References 1. J. C. Jones et al, Ferroelectrics. (1991), 121, 91-102. 2. D. Dunmur et al, J. Phys. E: Sci. Instrum. (1987), 20, 866. 3. J. C. Jones and E. P Raynes, Liq Cryst (1992), 11, 199-217.

P 18 UV stability of liquid crystal lasers during polymer stabilisation Shuyu Yang, Michael P. Shaver, Philip J.W. Hands a School of Chemistry, University of Edinburgh, King’s Buildings, Edinburgh, EH9 3FJ, UK a School of Engineering, University of Edinburgh, King’s Buildings, Edinburgh, EH9 3JF, UK

Dye-doped chiral nematic liquid crystal (LC) photonic band-edge lasers offer new disposable solutions for bespoke coherent light sources. Recent advancements include the gradient pitch LC laser [1], whereby a spatial variation in chiral pitch length (and dye concentration) across the cell, enables continuous wavelength tuning of the laser through simple variation of the spatial location of the focussed pump beam. Pitch gradients are formed through the diffusion of 2 lasing mixtures, each optimised for a different emission wavelength. Unfortunately, perpetual diffusion limits the stability of the pitch gradient for only a few weeks/months, ultimately decaying to a uniform pitch with no wavelength tuning capability. Polymer stabilisation has been hypothesised as an appropriate technique to fix pitch gradients and prevent further diffusion. Unfortunately, previous experiments have found that lasing is often no longer possible after polymer stabilisation, or occurs with significantly reduced performance [2]. This has been attributed to poor UV stability of the organic laser dyes, but has not been studied extensively.

Fig 1. Gradient-pitch LC laser (left). Images of different dye-doped LC laser cells with increasing UV exposure (right), with and without polymer-stabilisation (2% RM257, 0.5% Irgacure 819). The ticks and crosses denote successful and unsuccessful lasing achieved respectively. (Note NMR experiments determined minimum time for complete polymerisation is 1 minute at 46 mW/cm2).

This paper investigates the UV stability of a selection of organic dyes (DCM, PM597, PM597-8C9, PM650, Ph660) in LC lasers stabilised by the polymer RM257. We establish that UV damage is attributed to free- radical attack of the dye, caused by the presence of photoinitiator (Irgacure 819). Such damage reduces dye absorption/fluorescence capabilities and increases lasing thresholds. The effect is particularly pronounced in the popular dye DCM. However, alternative choices of dye (particularly pyrromethenes) were shown to be more resistant to such attack, beyond the timescales required for complete polymerisation of the sample (>1 min). This enables polymer stabilised gradient pitch LC laser systems to be successfully fabricated, with negligible effect upon laser performance. An additional note of discovery was that UV stability of LC lasers (containing no polymer) was far better than previously expected (exceeding 1 hour at 46 mW/cm2). This result bodes well for the future applications and commercialisation of LC laser sources.

References 1. S.M. Morris, P.J.W. Hands, et al., Optics Express, 16, 18827 (2008)

2. J. Schmidtke, W. Stille, et al., Advanced Materials, 14, 746 (2002)

P 19 The investigation of mixtures of dimers forming a N and a Nx/tb phase E. Ramou1,2, Z. Ahmed1, C. Welch1, G. H. Mehl1 1 Department of Chemistry, University of Hull, HU6 7RX, UK 2 Department of Physics, University of Patras, 26504 Patras, Greece

The investigation of an additional thermotropic LC phase, termed often either Nx or Ntb, found in dimeric liquid crystals below the nematic phase, has attracted considerable interest over the last few years. This Nx/tb phase is typically characterized by POM textures easily taken for that of a smectic phase, but the absence of small angle reflections in X-ray data indicates a structure with features of a nematic phase. Solid state NMR data and optical thin film investigations are indicative of the presence of chiral structures. Some TEM data and electro-optical studies suggest the possibility of twist-bent arrangements, hence the identification as Ntb, however some of this data is still discussed controversially. Phase structures, such as a splay-bend or a chiral domain structure or others such as a nematic hexatic phase are a possibility too, thus the provisional term Nx phase. In order to investigate this question further, mixtures of a material reported to show an Nx phase with a conventional nematic dimesogen were carried out. Binary mixtures of cyanobiphenyl dimers that exhibit a Nu-Nx phase transition are reported and investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and for selected compositions by XRD studies. The initial liquid crystal dimers are the a,ω-bis(4,4’– 1 cyanobiphenyl)nonane (CB9CB) that is already reported to exhibit a weakly first order Nu-Nx 2 transition and its corresponding ether linked dimer CBO9OCB that exhibits only the Nu phase. For mixtures richer in CBO9OCB the Nx phase is monotropic, observed only on cooling. The phase identification and characterization is performed by POM, as the Nu-Nx transition is too weak to be captured by DSC scans. Furthermore it was found that the Nu-Isotropic and Isotropic-Nu transitions are exhibiting strongly biphasic regions. On the other hand, as the mixtures become richer in the CB9CB, the Nx phase starts to appear in the DSC scans as a weakly first order transition during cooling and heating. Moreover, for some of the mixtures the DSC scans multiple peaks for the Nu- Isotropic and Isotropic-Nu transitions, suggesting surprisingly complex transition behaviour. The phase diagrams constructed depict a linear dependence on the composition for the Nu-Isotropic and Isotropic-Nu transitions and a substantially linear behaviour for the melting point and the crystallization. As for the Nx-Nu and Nu-Nx transitions, the phase diagrams reveal a stabilization of the formation of the Nx phase at an almost fixed temperature for heating and cooling in the stability range of this phase.

E.R. acknowledges support by the EU through the ERASMUS+ Placements programme.

References [1] C.S.P. Tripathi, P. Losada-Perez, C. Glorieux, A. Kohlmeier, M.G. Tamba, G.H. Mehl, Phys. Rev.E (2011), 84, 041707. [2] C. T. Imrie and P. A. Henderson, Chem. Soc. Rev. (2007), 36, 2096.

P 20 Liquid Crystal Infiltrated Gyroid Optical Metamaterials J.A. Dolana,b, T.J. Athertonc, J.J. Baumbergb, U. Steinerd, and T.D. Wilkinsona aDepartment of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK bDepartment of Physics, University of Cambridge, Cambridge, CB3 0HE, UK cPhysics and Astronomy Department, Tufts University, Medford, MA 02155, USA dAdolphe Merkle Institute, University of Fribourg, 1700 Fribourg, Switzerland

Block copolymers consisting of two or more covalently tethered and chemically distinct homopolymers may self-assemble into a range of equilibrium morphologies by microphase separation. One such morphology is the gyroid, the only triply periodic constant mean curvature surface also to possess an intrinsic chirality (Figure 1). As the characteristic length scale of polymer self-assembly is often deeply sub-wavelength for visible light, block copolymer gyroids represent a fascinating route by which to fabricate truly three dimensional optical metamaterials1. Gold gyroids templated in this manner exhibit a striking range of optical properties imparted by the particular sub-wavelength structure. These properties include highly anisotropic linear and circular dichroism, and a directionally dependent plasma frequency which is greatly depressed from that of the constituent gold2. Furthermore, infiltration of the gyroid metamaterial with various dielectric media allows the tuning of its optical response across the visible spectrum3. However, when infiltrated with a nematic liquid crystal, not only is the optical response of the material modulated, but also an intriguing liquid crystal defect structure is templated4. We therefore present progress towards the characterisation of the optical properties of gold gyroid optical metamaterials infiltrated with nematic liquid crystals.

Figure 4: a) The single gyroid morphology viewed along b) the [100] chiral direction, c) the [111] chiral direction, and d) the [110] achiral direction1.

References 1. J.A. Dolan, B.D. Wilts, S. Vignolini, J.J. Baumberg, U. Steiner, and T.D. Wilkinson, Adv. Opt. Mater. (2015), 3, 12 2. S. Vignolini, N.A. Yufa, P.S. Cunha, S. Guldin, I. Rushkin, M. Stefik, K. Hur, U. Wiesner, J.J. Baumberg, and U. Steiner, Adv. Mater. (2012), 24, OP23 3. S. Salvatore, A. Demetriadou, S. Vignolini, S.S. Oh, S. Wuestner, N.A. Yufa, M. Stefik, U. Wiesner, J.J. Baumberg, O. Hess, and U. Steiner, Adv. Mater. (2013), 25, 2713 4. T. Atherton, BLCS 2015 Oral Presentation

P 21 Developing Conductive Organic Molecular Resists for Nanofabrication of Insulating Materials Dennis Zhaoa, Greg O’Callaghana, Owen Jonesa, Farhan Hasanb, Karolis Virzbickasb, Jon A. Preecea and Alex P. G. Robinsonb aSchool of Chemistry, University of Birmingham, Edgbaston, Birmingham, UK bSchool of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, UK

Electron beam lithography can be used to pattern feature smaller than 10 nm. However, reaching this length scale has only been possible on conducting surfaces, e.g. silicon wafers. On insulating substrate such as glass or low conductivity samples such as GaN charging limits the resolution of electron beam lithography. Whilst photolithography can be used in some applications it is not appropriate for low volume high value manufacture. Therefore in order to mitigate charging, and enable the use of electron beam lithography on such substrates it is necessary to use a discharge layer, such as thin film of metal underneath or on top of the resist. However, such measures limit resolution in themselves, and can also damage device performance11. Sub 100 nm has not been achieved for insulating materials such as GaN and glass using electron beam lithography.

In this work we are developing resist materials that are inherently conductive. Here we describe the synthesis of triphenylene cored resist for use in EBL as candidates for nanostructuring insulating materials. The triphenylene’s liquid crystalline behaviour, delocalised electrons and excellent electron transport make them appealing candidates to be able to not only act as a resist, but also as a charge dissipater.

[11] Z. Cui, Nanofabrication Principles Capabilities and Limits, 2008, 1st ed., Berlin: Springer, 220-250

P 22 Polarization-independent switchable liquid crystal lenses based on the dark conglomerate phase H. Miltona, M. Nagaraja, S. Kaurb, J. C. Jonesa,b, P. B. Morganc and H. F. Gleesona,b aSchool of Physics and Astronomy, University of Manchester, Manchester M13 9PL bSchool of Physics and Astronomy, University of Leeds, Leeds LS2 9JT cEurolens Research, Faculty of Life Sciences, University of Manchester, Manchester M13 9PL

Liquid crystal lenses are an emerging technology that can provide variable focal power in response to applied voltage. However, an issue with many nematic liquid crystal lens designs is that they are polarization dependent, with only 50% of unpolarised light being subject to the variable change in focal power. This makes polarization-independent technologies very attractive. One of the ways to achieve that is using electro-optic modes of optically isotropic materials.

Recently, the dark conglomerate (DC) phase, which is an optically isotropic liquid crystalline state, has been shown to exhibit a large change in refractive index in response to an applied electric field [1]. This unusual change in the refractive index which has not been reported before in the DC phase of other liquid crystals occurs because of a series of electric-field-driven transformations that take place in the DC phase of the studied bent-core liquid crystal. We present computational modelling of the electrostatic solutions for two different types of 100 μm diameter liquid crystal lenses – microlenses and flat GRIN lenses, which include the DC phase. A feature of the field dependence of the refractive index change in the DC phase is that it is approximately linear in a certain range, leading to the prediction of excellent optical quality for driving fields in this regime. A simulated microlens shows two modes of operation: a positive lens based upon a uniform bulk change in refractive index at high voltages, and a negative lens resulting from the induction of a gradient index effect at intermediate voltages. On comparing the simulated microlenses and flat GRIN lenses, the main difference is in the variability of focal power that can be achieved. In the case of the flat GRIN structure, the focal power can be varied continuously between 0 D and -83.5 D, while the microlens device chosen as an exemplar is restricted to three optical states: 0 D, -85 D, and -20 D. The work illustrates that the DC phase has excellent potential for the development of a new class of polarization independent switchable liquid crystal lenses.

References 1M. Nagaraj, K. Usami, Z. Zhang, V. Görtz, J. W. Goodby and H. F. Gleeson, Liq. Cryst. (2014), 41, 800.

3H. E. Milton, M. Nagaraj, S. Kaur, P. B. Morgan, J. C. Jones and H. F. Gleeson, Appl. Optics (2014), 53, 7278.

P 23 Colloid – Liquid Crystal Gels

T. A. Wood, J. S. Lintuvuori, A. B. Schofield, D. Marenduzzo, W. C. K. Poon

School of Physics and Astronomy, James Clerk Maxwell Building, University of Edinburgh, EH9 3JZ [email protected]

Abstract: Liquid crystalline materials occur in aqueous solutions of surfactant, DNA, peptide solutions, lipids and drugs in addition to the thermotropic materials used in liquid crystal displays. In many multicomponent biological systems and commercial formulations colloids are combined with liquid crystalline phases – therefore it is important to understand interactions between colloids and liquid crystals. The nematic phase has orientational order and any defects caused by shear relax over time as the phase equilibrates. Immersing particles within a nematic phase creates defects since the uni- directional nematic must accommodate the surface morphology of the particle. We examine the range of gel structures that form when hard-sphere colloids are dispersed in the nematic phase of 5CB. Through experiments and computer simulations we show that, when the surfaces of particles support homeotropic anchoring in a nematic solvent, colloidal structure is sensitive to concentration. Elastic mediation results in chain-like structures at very low volume fractions,  < 2%. At intermediate volume fractions, 2% <  < 22%, multi-particle clusters form and gather to form a percolating colloidal gel. For  > 22% the colloids are knitted together by percolating lines of defects that extend through the sample and lead to high elasticity [1]. All these structures are deeply metastable with percolating structures that persist for longer than 1 year.

Figure 1: Appearance of colloid dispersions in 5CB for different concentrations (A) in a vial after 10 months, from left to right  = 1%, 3% and 5% (B) a drop of  = 3% on a slide showing heterogeneous macroscopic texture (C) a spread drop of  = 33% showing a smooth macroscopic texture. Confocal images of (D) the chain-like structures at  = 0.5%, (E) percolating colloidal clusters at  = 6% and (F) a densely knitted structure at  = 33%.

P 24 The effect of a methylene link in the flexible spacer of liquid crystal dimers Jordan P Abberley, John MD Storey and Corrie T imrie Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Aberdeen AB24 3UE, UK

The twist bend nematic phase was recently identified for methylene-linked cyanobiphenyl-based liquid crystal dimers[1,2] and the structure confirmed in studies based on freeze fracture transmission [3,4] electron microscopy. In the Ntb phase, the achiral molecules form a helix and the director is tilted with respect to the helical axis. The induced twist may be either left or right handed and equal amounts of both types of helix are expected. The Ntb phase had previously been predicted to exist for bent molecules by Dozov who suggested that in a nematic phase the director may bend around bent molecules.[5] To stabilise such a bend, either splay or twist must be introduced, resulting in two new nematics with nonuniform director distributions, splay-bend or twist-bend.

The twist-bend nematic phase has been reported for just a small number of compounds and so the development of the empirical relationships linking molecular structure to the observation of this exciting new phase is at a very early stage. However, all the compounds reported to date have a bent molecular shape, and the majority of these are dimers containing methylene-linked spacers, which accentuate the molecular bend. It was believed that this was an essential structural feature to [6] observe the Ntb phase, however, an ether-linked dimer has also been shown to exhibit the phase.

We recently showed that a methylene-ether linked spacer could also support the formation of the Ntb phase and here we compare the properties of a set of compounds containing such a spacer:

with those of the corresponding ether linked materials:

The transitional properties of these materials have been determined using polarized light microscopy and differential scanning calorimetry. The differences in their properties are attributed to differences in their average molecular shapes. References [1] V.P. Panov, M. Nagaraj, J.K. Vij, Y.P. Panarin, A. Kohlmeier, M.G. Tamba, R.A. Lewis, G.H. Mehl, Phys. Rev. Lett. 2010, 105, 167801. [2] 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, J. Salud, B. A. Timimi, H. Zimmermann H, Phys. Rev. E 2011, 84, 031704. [3] V. Borshch, Y. K. Kim, J. Xiang, M. Gao, A. Jakli, V. P. Panov, J. K. Vij, C. T. Imrie, M. G. Tamba, G. H. Mehl, O. D. Lavrentovich, Nat. Commun. 2013, 4, 2635. [4] 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, J. E. Maclennan, N. A. Clark, Proc. Nat. Acad. Sci. USA 2013, 110, 15931-15936. [5] I. Dozov, Europhys. Lett. 2001, 56, 247-253. [6] R. J. Mandle, E. J. Davis, S. A. Lobato, C. C. A. Vol, S. J. Cowling, J. W. Goodby, Phys. Chem. Chem. Phys. 2014, 16, 6907-6915.

P 25 Application of EPR Spectroscopy and Molecular Dynamics Simulations to a Lyotropic Liquid Crystal – A Combined Approach Christopher Prior a and Vasily S. Oganesyan a aSchool of Chemistry, University of East Anglia, Norwich, NR4 7TJ, U.K. [email protected]

Electron Paramagnetic Resonance (EPR) with paramagnetic spin probes combined with molecular modelling have proved to be a particular useful approach for the study of the dynamics and molecular organisation in nematic and discotic thermotropic liquid crystals1-3. Here we report the first application of a combination of EPR spectroscopy and MD simulations to sodium dodecyl sulphate (SDS) lyotropic systems doped with the 5-DOXYL stearic acid (5DS) nitroxide spin probe. The SDS systems include pre-micellar, micellar and rod aggregations. Fully atomistic MD simulations have been carried out using the General AMBER Force Field (GAFF) and ChElPG scheme for partial charges and the TIP4P-Ew water model. EPR spectra are predicted directly from these MD trajectories using our MD-EPR simulation methodology4,5. Predicted motions for different surfactant aggregations and the resulting EPR lineshapes show good agreement with experiment and demonstrate the advantages of using a combined MD-EPR approach for providing a new level of detail in molecular motions and order. In particular, the results show that 5DS probe has anisotropic (axial) rotational correlation times, when doped in both SDS micelles and rods, and serves as a sensitive reporter of the local molecular environment. This study uncovers the potential for such a synergistic approach to provide information about the changes in the sizes and motions of surfactant aggregates across the phase transition regions.

SDS Micelle

Rod

Exp. Sim. (MD)

References 1. F. Chami, M. R. Wilson, V. S. Oganesyan, Soft Matter (2012), 8, 6823. 2. H. Gopee, A. N. Cammidge, V.S. Oganesyan, Agnew. Chem. Int. Ed. (2013), 52, 8917. 3. V. S. Oganesyan, E. Kuprusevicius, H. Gopee, A. N. Cammidge, M. R. Wilson, Phys. Rev. Lett. (2009), 102, 013005.

4. V. S. Oganesyan, Phys. Chem. Chem. Phys. (2011), 13, 4724. 5. V. S. Oganesyan, J. Magn. Reson. (2007), 188, 196.

P 26 Conductive Resists for Nanofabrication on Insulating Substrates F. Hasan a, G. O'Callaghan b, J.A. Preece b, A.P.G. Robinson a a School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK b School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK

Electron beam lithography (EBL) has the capability for extremely high-resolution patterning, mask making for photolithography, low-volume high-value manufacturing, prototyping and other nanotechnology research. In EBL electrons are used for patterning, therefore it is ideal to use conductive substrates. However, if the substrate is an insulator (e.g. glass), or made with poor conducting materials (e.g. GaN) patterns become distorted and misaligned due to the buildup of charge in the substrate. Traditionally this issue has been treated by using a metal-coated discharge layer under or over the resist or an organic conductor mixed into the resist. Previous studies indicate that a conductivity of ~10-2 S/m is required to achieve acceptable charge dissipation [1].

Due to increased process complexity and poor resolution with the approaches described above, we are developing an electron beam resist which is an inherently conductive material. Previously we have demonstrated an epoxy derivative of triphenylene, which is highly sensitive and capable of patterning below 20 nm feature sizes [2]. Triphenylene derivatives are well known as excellent photoconductors [3], and due to their hexagonal columnar discotic liquid crystal structure [4] they show fast hole mobility (e.g. 10-3 cm2V-1s-1) [5] along the columns. Therefore this project aims to develop a triphenylene derivative with high conductivity and at the same time good lithographic properties.

Initial experiments with 2,3,5,6,10,11-hexapentyloxy-triphenylene have been performed. The material forms good quality films by spin coating on glass and silicon substrates. The sensitivity of the material is found to be ~4 mC/cm2 without chemical amplification (CA) and a resolution of 14 nm isolated (Fig. 1) and 20 nm half pitch (Fig. 2) has been achieved on silicon substrates at 28.8 nC/cm dose in a 28 nm film. Fig. 3 shows 40 nm half-pitch with 339 pC/cm dose on a 26 nm thick CA film and the sensitivity of this CA resist has been found 25.9 μC/cm2. Fig. 4 shows the first patterning results on a poor conductivity substrate – a linewidth of 35 nm achieved on a nm GaN on sapphire substrate.

Fig. 1. 14 nm pattern in a 28 nm thick film at 31.6 nC/cm dose.

P 26

Fig. 2. 20 nm half pitch lines in a 28 nm film at 28.8 nC/cm dose.

Fig. 3. 40 nm half pitch lines in a 26 nm CA film at 339 pC/cm dose.

Fig. 4. 35 nm line patterned on GaN on Sapphire at 8 mC/cm2.

References [1] M. Angelopoulos, J. M. Shaw, R. D. Kaplan, and S. Perreault, JVST B. 7 (1989) 1519. [2] H.M. Zaid, A.P.G. Robinson, R.E. Palmer, M. Manickam and J.A. Preece, Adv. Funct. Mater., 17, 2522 (2007) [3] F. Closs, K. Siemensmeyer, T. Frey and D. Funhoff, Liquid Crystal, 14 (1993), 629. [4] M. T. Allen, S. Diele, K. D. M. Harris, T. Hegmann, B. M. Kariuki, D. Lose, J. A. Preece, and C. Tschierske, Journal of Materials Chemistry 11 (2001), 302-311. [5] M. Inoue, H. Monobe, M. Ukon, V.F. Petrov, T. Watanabe, A. Kumano, and Y. Shimizu, Opto-Electronics Review, 13 (2005), 4, 303–308.

P 27 Numerical Modelling of Cholesteric Droplets Menyang Yang, Prashant Patel, F. Anibal Fernandez and Sally Day Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE UK

Numerical modelling has been carried out to simulate the structures of cholesteric liquid crystals confined in droplets. The variable order modelling methods used [1,2] allow the formation and movement of defects within the structure; the surface alignment can be set at the surface of the droplet. Initially nematic liquid crystal were simulated in spherical and oblate droplets, with planar degenerate anchoring at the surface of the droplet. The formation of defects at the poles of the droplets were found and, as expected, the defects form at the regions of highest curvature in the oblate droplets. Spherical droplets were then used to model the cholesteric structures. The twist in the director was found to be largely uniform in one direction, but the structure in the other directions becomes distorted. Variation in the structure with strength of surface alignment has also been simulated. Investigation of the required number of nodes was investigated and as a result the modelling is currently carried out on relatively small structures, but with longer simulation times larger droplets could be modelled. The optical properties of the larger structures will show the characteristic selective reflection.

References 1. James, R; Willman, E; Fernandez, FA; Day, SE; (2008) IEEE TRANSACTIONS ON MAGNETICS , 44 (6) 814 - 817. 2. James,R, Willman,E, Fernandez, FA and Day,SE (2006) IEEE T. Electron Devices, 53 (7) 1575-1582..

P 28 A c2mm Liquid Crystal Phase Formed by Dimer Molecules

Warren Stevenson a, Ziauddin Ahmed b, Xiangbing Zeng a, Goran Ungar a and Georg Mehl b

a Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield

b Department of Chemistry, University of Hull, Cottingham Road, Hull

In recent years the nematic – nematic transition observed in LC dimers with an odd spacer has attracted significant attention. The theorised existence of helical chirality within the lower temperature nematic, often termed the Nx or Ntb phase, has been the primary focus of investigation. To date the proposed conical helices continue to elude unambiguous identification through conventional characterisation techniques; as such we turn our attention to the liquid crystal (LC) phases formed below the Nx. Here we present a modulated smectic c2mm LC phase formed upon cooling the Nx phase of DTC7C5 through a first order phase transition. This phase was characterised through grazing incidence and transmission X-ray scattering experiments which reveal a centred rectangular unit cell (spacegroup c2mm) with lattice parameters ‘a’ = 27.21 ± 0.07nm (modulation wavelength) and ‘b’ = 4.145 ± 0.007nm (layer spacing). We propose that the periodic step in the molecular arrangement originates from local splay in a similar fashion to the B1 banana phase of polar bent core mesogens. However in contrast to the B1 phase the step does not create layer discontinuity, but instead produces interlocked double layers. The (11) and (02) lattice spacing of these double layers were found to respectively coincide with the ~1.9 and ~4nm scattering maxima observed within the Nx phase. This, as well as the similarity in POM textures, may suggest that the two phases are in fact closely related. This work may therefore bring us a step closer to determining the true structure of Nx phase.

Nx Phase c2mm Phase

1.89nm (02)

3.98nm (31)(51) (11) Cooling (40) (20)

P 29 An isothermal nematic to twist-bend nematic phase transition Daniel A. Paterson, A. Martinez-Felipe, R. Walker, J. M. D. Storey, and C. T. Imrie

Department of Chemistry, University of Aberdeen, Meston Walk, AB24 3UE, UK.

The twist-bend nematic phase (Ntb) has recently been observed in liquid crystal dimers which consist of molecules in which two mesogenic units are separated by an odd-membered methylene- 1 linked flexible spacer . In the Ntb phase, the achiral molecules form a helix and the director is titled with respect to the helical axis. The Ntb phase had previously been predicted to exist for bent molecules by Dozov and its formation attributed to a bend elastic constant (K33) which tends towards zero2.

Recently molecules containing ether linkages in the spacer have been found to exhibit twist-bend nematic behaviour3,4. This prompted us to consider methylene-ether linked spacers and these also 5 support the formation of the Ntb phase . Here we report the synthesis and charcterisation of a dimer containing an azobenzene moiety linked to a cyanobiphenyl unit by a methylene-ether flexible spacer:

The dimer exhibits two mesophases; the lower temperature mesophase is the twist-bend nematic phase attributed to the bent shape of the molecule; whilst the higher temperature is assigned as a typical nematic phase. An isothermal Ntb - N phase transition is observed on photoisomerising the azo linkage in the dimer.

Figure 1. CB6OABOBu

Figure 2. Ntb phase exhibited by CB6OABOBu at 105 °C

References 1. Cestari, M., Diez-Berart, S., Dunmur, D. A., Ferrarini, A., de la Fuente, M. R., Jackson, D. J. B., Lopez, D. O., Luckhurst, G. R., Perez- Jubindo, M. A., Richardson, R. M., Salud, J., Timimi, B. A., and Zimmerman, H., 2011, Phys. Rev. E, 84, 031704. 2. Dozov, I., 2001, Europhys. Lett., 56, 247. 3. Mandle R. J., Davis E. J., Lobato S. A., Vol C. C. A., Cowling S. J., Goodby J. W. PCCP. 2014;16(15):6907-6915. 4. N. Sebasti´an, D. O. L´opez, B. Robles-Hern´andez, M. R. de la Fuente, J. Salud, M. A. P´erez-Jubindo, D. A. Dunmur, G. R. Luckhurst and D. J. B. Jackson, Phys. Chem. Chem. Phys., 2014, 16, 21391–21406. 5. Jansze S. M., Martinez-Felipe A., Storey J. M. D., Marcelis A. T. M., Imrie C. T., Angew. Chem. Int. Ed. 2015;54(2):643-646.

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