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Soft Matter Research at Upenn Organize Anisotropic Bullet Shaped Particles Into 1D Chains 2D Hexag- Onal Structures (3)

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Soft Matter Research at Upenn Organize Anisotropic Bullet Shaped Particles Into 1D Chains 2D Hexag- Onal Structures (3) Marquee goes here Soft Matter Research at UPenn organize anisotropic bullet shaped particles into 1D chains 2D hexag- onal structures (3). They have also shown that controlling boundary conditions and particle shape can allow the creation of hybrid washers which combine homeotropic and degenerate planar anchoring (4). The washers change their angle with respect to the far-field direction and are capable of trapping spherical colloids, allowing for the construc- tion of multi-shape colloidal assem- blages. These methods can be used to create complex shapes, further in- creasing the number of techniques Background image: An illustration of edge-pinning effect of focal conic domains (FCDs) in smectic-A liquid crystals available to those involved in creat- with nonzero eccentricity on short, circular pillars in a square array, together with surface topography and cross-polarized optical image of four FCDs on each pillar. The arrangement of FCDs is strongly influenced by the height and shape of the ing complex structures. pillars. Image courtesy of Felice Macera, Daniel Beller, Apiradee Honglawan, and Simon Copar. Advanced Materials Cover: This paper demonstrated an epitaxial approach to tailor the size and symmetry of toric focal conic domain (TFCD) arrays over large areas by exploiting 3D confinement and directed growth of Smectic-A liquid The team is actively contributing crystals with variable dimensions much like the FCDs. to the goals of the MRSEC by ex- panding the techniques available At the Materials Research Science The coalition has published sev- for use in the construction of com- & Engineering Center (MRSEC) at eral papers together. They have plex assemblies. Their work also the University of Pennsylvania, three worked on demonstrating how provides a firm footing for planning research groups are hard at work Smectic-A liquid crystals respond future projects, giving researchers a figuring out some of the fundamen- to underlying substrate geometry, broader array of methods and tech- tal physics behind liquid crystal ma- allowing grapho-epitaxial assem- niques. terials of soft matter materials. Pro- bly of toric focal conic domains of Learn more about their collabora- fessors Kate Stebe, Randy Kamien, smectic-A liquid crystals (1). They tion at the group website. and Shu Yang each head up a re- furthered this line of thought by -Michael Lane search group, and collaborate at the showing how liquid crystal film university. The goal of the MRSEC is thickness and pillar height affect for- 1. “Pillar-Assisted Epitaxial Assembly of Toric Focal Conic Domains of Smec- tic-A Liquid Crystals”, A.Honglawan , D.A. Beller , M.Cavallaro , R.D. Kamien , to preemptively obtain knowledge mation of hierarchical assembly of K.J. Stebe , and S.Yang, Advanced Materials, 2011, 23, 5519–5523 2. “Topographically induced hierarchical assembly and geometrical transfor- that will be useful to future applica- such domains (2). The results from mation of focal conic domain arrays in smectic liquid crystals” Apiradee Honglawana, D.A. Bellerb,1, M.Cavallaro, Jr.a, Randall D. Kamienb, K. J. Ste- tions of soft matter materials. Other these studies will be useful to future be, and Shu Yanga,c,2 PNAS, 2013, 110 (1) 3. “Microbullet assembly: interactions of oriented dipoles in confined nematic senior investigators involved in re- attempts to create complex 3D de- liquid crystal.” M.A.Gharbia,b,c , M.Cavallaro Jr.b , G.Wuc , D.A. Bellera , R.D. Kamiena ,S.Yang, and K.J. Stebeb. Liquid Crystals, 2013 lated work in the MRSEC group on signs, allowing further development 4. “Ring Around the Colloid”, Marcello Cavallaro Jr.,M.A. Gharbi,D. A. Beller,S Copar, Z.Shi, R.D. Kamien,Shu Yang,Tobias Baumgart, geometric routes to soft assembly of LC-based electronics and optical and Kathleen J. Stebe. include Professors Tom Lubensky, devices. Arjun Yodh, Peter Collings, Denis The groups have demonstrated Discher, Ravi Radhakrishnan and To- that electric fields can be used to bias Baumgart. Morphology transition in lipid vesicles due to in-plane order and topological defects Linda S. Hirst, Adam Ossowski, Matther Fraser, Jun Geng, Jonathan Selinger, and Robin Selinger. PNAS (2013) vol. 110 no. 9. 3242-3247 dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid GUVs formed in water via the electro-formation meth- od. To provide evidence for topological defects in the vesicles, DPPC GUVs were labeled with a polarization sensitive molecular probe (Laurdan) which aligned parallel to the tilt orientation of the surrounding lipids. The probe fluoresced with varying intensity in different domains dependent on the angle of polarizer rotation. This provided evidence that the lipid tilt orientation var- ied as a function of position around the vesicle. An additional experiment was designed to observe whether the crumpled vesicles remained intact across the liquid crystalline (Lα) to gel (Lβ’) phase transition by dispersing vesicles in an aqueous solution containing fluorescent dextran. The vesicles were dispersed while in the gel phase then cooled to room temperature into the liquid crystalline phase and observed using con- focal microscopy (Figure 1c-d). The images showed a Figure 1 A-B: Two flourescence microscopy images of the DPPC GUVs in their crumpled state after cooling to room temperature (Scale bars, 10 μm). distinct contrast between the exterior red dye solutions Figure 1C: confoncal microscopy image of a GUV which had fractured whilst cooling into its gel phase (Lβ’). against the dark interior of the crumpled vesicles (Fig- Figure 1D: a less topologically deformed sample, remained intact throughout its mem- brane wall keeping the red dye from leaking in ure 3d). Despite a number of instances where crumpled Figure 2: A coarse grained model of a GUV used to investigate the two competing mecha- nisms responsible for surface morphology. The parameters support the hypothesis as GUV GUVs fractured (Figure 3a typically in vesicles with larg- B is markedly more deformed than A. The numbers above the images represent angle of view. er radii or highly deformed samples) a majority of the 2A: A system with high defect mobility and slower membrane motion. 2B: A system with low defect mobility and faster membrane motion. crumpled membranes remained intact. The relationship between complex shapes and topo- The coarse-grained model was designed to provide logical defects has been identified and studied in soft insight into the competing mechanisms responsible for matter systems for some time. Liquid crystals, block co- inducing defects and the resulting crumpled morphol- polymer vesicles, liquid-crystalline elastomers, colloidal ogy. The parameters assumed a fluid, non-hexatic bond crystals and superfluids are some interesting examples. orientation. The simulation provided evidence that the Typically, such phenomena arise from the chemically extent of crumpling is determined via kinetic competi- heterogeneous nature of these systems. In this paper, tion between defect mobility and changing membrane researchers present a new study on chemically ho- curvature. If defect mobility is fast compared with mem- mogenous giant unilamellar vesicles (GUVs) which dis- brane motion, or if the vesicle size is relatively small play significant morphological changes (referred to as (Figure 2a), then all extra defect pairs quickly annihi- crumpled vesicles as seen in Figure 1a-b) as they cool late before the overall membrane shape has changed through the liquid crystalline (Lα) to gel (Lβ’) phase tran- significantly and a vesicle reaches the prolate ground sition. state with only two defects. However, if defect mobility is relatively slow compared with membrane translation, The authors propose that the complex crumpling is or if the vesicle size is larger, defects become trapped in driven by topological defects in the lipid tilt orientation. deeply metastable states and the vesicle forms a crum- In order to properly test their hypothesis they employed pled morphology with non-uniform Gaussian curvature a dual approach of computational (Robin Selinger and (Figure 2b). Visit the SMW website to watch a video of Johnathan Selinger Kent State) coarse grained simula- this. tions and experimental fluorescence microscopy tech- niques (Hirst Group UC Merced). Visit PNAS to read more. The experimental portion of the study focused of -Adam Ossowski September | 2013 | Issue #56 2 SOFTMATTERWORLD.ORG PRESENTS 2014 CALENDar COMPETITION caLL FOR imaGES Submission of images for the 2nd Annual SoftMatter- World Calendar Competition is now open. This year we have improved the submission system by adding a form to the Gallery section of the website where you can directly upload your images, captions and author imformation. The deadline is November 30th, 2013. This will be strictly followed. The calendars must be printed before the holidays to allow ample time for shipping in- ternationally. Should you have any issues with the form online, please email: [email protected] We would like to thank the 12 users who submitted their images last year. We extend our appreciation not only for their contribution, but their patience and en- thusiasm as well. This year’s flyers and posters are com- posed with images from last years calendar and can be downloaded in a press package on the website. Most importantly, remember that here are only two criteria which have to be fulfilled in order for an image to be considered: Soft Matter and Art Visit the Soft- MatterWorld.org gallery for some great inspiration. I-CAMP liquid
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