Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B30: Liquid Crystals IFocus
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Sponsoring Units: GSOFT Chair: Cristina Martin Linares, Johns Hopkins University Room: BCEC 162B |
Monday, March 4, 2019 11:15AM - 11:27AM |
B30.00001: Liquid-Liquid Interfaces and Grain Boundaries Engineering of Soft Crystals Xiao Li, José A. Martínez-González, Xuedan Ma, Orlando Guzmán, Kangho Park, Juan De Pablo, Paul F Nealey In solid state science, a considerable challenge remains in the development of techniques toward grain-boundary engineering, which is fundamental for designing materials with specific mechanical properties. Meanwhile, in soft matter a significant number of natural phenomena take place at liquid-liquid interfaces. Similar to grain boundaries of solid crystals, liquid-liquid interfaces lack of shape control, placing limits to applications in biosensing, photonics, directed self-assembly and adsorption phenomena. In this work, we build on soft-matter heteroepitaxy to grow, not solids, but single crystals of cubic liquid-crystalline BPs. Specifically, we rely on accurately designed binary-anchoring patterned substrates that facilitate spontaneous BP nucleation over the whole patterned region. This leads to a distortion-free BP-soft crystal, with a uniform lattice orientation that depends on the symmetry of the pattern used. Based on such liquid-liquid interfacial behavior, we produce large, stable and single-crystal BP-domains can serve as an alternative for engineering materials with accurately localized regions that respond sensitively to contaminants, incident light, electric or magnetic fields and other external stimuli. |
Monday, March 4, 2019 11:27AM - 11:39AM |
B30.00002: Cylindrical fiber cored by a double twisted chiral nematic Adrian Reyes, Gerardo J. Vázquez Abstract |
Monday, March 4, 2019 11:39AM - 11:51AM |
B30.00003: First-order smectic-hexatic phase transition in thick liquid crystal films Ivan Zaluzhnyy, Ruslan Kurta, Nastasia Mukharamova, Young Yong Kim, Ruslan Khubbutdinov, Dmitry Dzhigaev, Vladimir Lebedev, Elena Pikina, Efim Kats, Noel Anthony Clark, Michael Sprung, Boris Ostrovskii, Ivan Vartanyants Synchrotron studies with a focused x-ray beam of the first-order smectic-A – hexatic-B (Sm-A – Hex-B) phase transition in 2-10 μm thick free standing films of 54COOBC compound are presented. The Hex-B phase is distinguished from Sm-A phase by long-range bond-orientational (BO) order, which can be conveniently studied by the angular X-ray cross-correlation analysis (XCCA). Discontinuity in temperature dependence of positional correlation length and the BO order parameter as well as direct observation of phase coexistence clearly indicate the first-order character of the phase transition. Experimental data unambiguously show that the width of temperature region of two phases coexistence increases with film thickness. This effect is explained on the basis of Landau mean-field theory in the vicinity of a tricritical point by anomalous penetration of the Hex-B order parameter into the film interior. |
Monday, March 4, 2019 11:51AM - 12:03PM |
B30.00004: Liquid Crystal Flat Optical Elements Ziyuan Zhou, Miao Jiang, Hao Yu, Yubing Guo, Taras Turiv, O D Lavrentovich, Qi-Huo Wei Thin liquid crystal films (LCs) with well-defined molecular orientations are an exceptional platform for making flat optical devices based on the Pancharatnam-Berry phase. Here we present a new approach to designing and fabricating liquid crystal flat optical elements such as micro-lenses and beam-shapers. We show the molecular orientation patterns for shaping a light beam into desired intensity profiles can be designed using a generalized Snell’s law, and that such liquid crystal flat optical elements can be made with high throughput and high resolution by using a plasmonic-metamask-based photopatterning approach. |
Monday, March 4, 2019 12:03PM - 12:15PM |
B30.00005: Cellulose Nanocrystals confined to polymer microgels Sujin Lee, Elsa Reichmanis, Mohan Srinivasarao, Jung Ok Park Liquid crystals that are confined within curved boundaries are of interest to many scientists due to their important role in optoelectronic technologies. As such, intensive research has been conducted with various types of liquid crystals constrained to droplets or cylindrical environments. Such studies are significant because the curvature of liquid crystals costs elastic energy, and hence, we observe rich physical phenomena such as change in the director field that otherwise would have been hidden. Most of the fundamental studies of liquid crystalline phase of the cellulose nanocrystals were conducted as a film type or in the cells with flat boundaries, limited to certain concentrations. Here, we report cellulose nanocrystals confined to pnipam microspheres using inverse emulsion polymerization technique with microfluidics device. The chiral nematic phase of cellulose nanocrystals are preserved within the polymer matrix, as characterized by optical microscopy. The droplet radius, R of the microgels can be adjusted by changing the volumetric flow rate of oil phase in a microfluidics device. Notably, the fabricated CNCs-PNIPAM microgels are able to exhibit swelling-deswelling behavior upon temperature change with well-organized structure. |
Monday, March 4, 2019 12:15PM - 12:27PM |
B30.00006: Anisotropic diffusion of islands and topological defects in dipolar chains of islands in freely-suspended SmC liquid crystal films Cheol Park, Eric Minor, Joseph E MacLennan, Matthew Glaser, Noel Anthony Clark Islands, disk-like inclusions of extra layers in few-layer thick, freely-suspended tilted smectic liquid crystal films, stabilize +2π chiral vortices in the two-dimensional XY field giving the azimuthal orientation of the local molecular tilt. We have studied the Brownian motion of islands and their companion - 1 defects on the background film in a dipolar chain of islands. The mean square fluctuations of the position are strongly anisotropic, the island mobility parallel to the chain direction being up to four times smaller than their mobility perpendicular to the chain. Measurements of thermal fluctuations of islands and topological defects in dipole chains will be compared with theoretical predictions. |
Monday, March 4, 2019 12:27PM - 12:39PM |
B30.00007: Two-Dimensional Hexagonal Boron Nitride Nanosheet as an Ion-Capturing Planar-Alignment Agent in a Liquid Crystal-Based Electro-Optic Device Rajratan Basu, Lukas Atwood The two-dimensional (2D) hexagonal boron nitride (h-BN) nanosheet is employed as a planar-alignment agent on one side of a liquid crystal (LC) cell, where the other side of the cell has a standard planar-aligning polyimide (PI) layer. The LC exhibits uniform planar-alignment in this h-BN/PI hybrid cell. The free-ion impurities in the LC are found to be suppressed dramatically in this h-BN/PI hybrid cell compared to that in a standard PI/PI LC cell. The free-ion concentration is reduced in the hybrid cell due to the 2D h-BN nanosheet’s ion-capturing process. The reduction of ionic impurities results in an accelerated electro-optic response of the LC in the hybrid cell. The dielectric anisotropy of the LC is enhanced in the h-BN/PI hybrid cell, indicating an improved orientational order parameter of the LC due to the reduction of ionic impurities. |
Monday, March 4, 2019 12:39PM - 12:51PM |
B30.00008: Study of phase behavior and (meta)stability of model surfactant solutions by microfluidic thermal fluctuation platform Haoyu Wang, Sepideh Khodaparast, Joao Cabral Metastability poses considerable challenges for the practical utilisation of surfactant solutions subjected to ubiquitous temperature fluctuations. We first investigate aqueous solutions of a model biodegradable surfactant system (Linear Alkylate Sulfonate, LAS) at low concentrations, examining the mechanism and kinetics of the transition from micellar to multilamellar vesicle (MLV) phase, in the absence of salt and external flow. We then employ a novel microfluidic platform designed to rapidly modulate temperature fields and detect phase changes, coupled with optical microscopy and small angle neutron scattering (SANS). We resolve the MLV structure and decouple the nucleation and growth kinetics across the metastable zone width by imposing the square-wave temperature profiles. Finally, we demonstrate the imposition of complex temperature profiles, mirroring diurnal and seasonal variations, and their consequences to LAS micellar solution stability. |
Monday, March 4, 2019 12:51PM - 1:03PM |
B30.00009: Chiral symmetry-breaking dynamics in the phase transformation of nematic droplets Nasser Abukhdeir, Fred Fu Chiral symmetry-breaking equilibrium textures in deformable and nondeformable droplets of achiral nematic liquid crystals (LCs) have long been observed for a broad range of LC compounds and conditions. Most of the observed chiral symmetry-breaking phenomena in achiral nematic LCs have involved spherical nematic droplets, which serve as ideal geometries for studying the interaction between surface and bulk elastic effects on nematic texture. |
Monday, March 4, 2019 1:03PM - 1:15PM |
B30.00010: Brownian Dynamics of Particles “Dressed” by Chiral Director Configurations in Lyotropic Chromonic Liquid Crystals Angel Martinez, Peter Collings, A. G. Yodh We employ video microscopy to study the Brownian dynamics of colloidal particles suspended in the uniaxially aligned nematic phase of a lyotropic chromonic liquid crystal (LCLC), Disodium Cromoglycate (DSCG). DSCG is water soluble, and its nematic phase is characterized by an unusually large elastic anisotropy. Our measurements of the mean-square displacement for polystyrene-based colloidal microspheres show sub-diffusive behaviors along directions parallel and perpendicular to the nematic director. The dynamics parallel to the far-field director is sub-diffusive for lag times as long as several seconds and then diffusive beyond that, while the dynamics perpendicular to the far-field director continues to display complicated and unexpected sub-diffusive behavior for hundreds of seconds of lag time. Also, spherical colloids suspended in LCLCs can induce two symmetrically and energetically distinct director field configurations and we consider the effects of these differences on the diffusion dynamics of LCLC colloids. The origin of these deviations from conventional diffusion theory are discussed and our results are compared to previous diffusion experiments in conventional nematic liquid crystals. |
Monday, March 4, 2019 1:15PM - 1:27PM |
B30.00011: Interaction of liquid crystal skyrmions with curved boundaries Avadh Saxena, Ayhan Duzgun A liquid crystal cell is made by confining the liquid crystal material between two plates usually made of glass. In recent years, long-lived skyrmions, which are topological defect structures of the director field, have been realized in chiral nematic liquid crystal cells by means of establishing equilibrium between a background electric field and surface anchoring. These skyrmions interact with each other as well as with field gradients. In this work, we present numerical studies where an additional electric field, surface anchoring or light is used to generate “walls” to guide the motion of skyrmions. Specifically, we explore the motion of skyrmions near curved boundaries and how it is affected by the curvature. |
Monday, March 4, 2019 1:27PM - 1:39PM |
B30.00012: Magnetic Effects in Confined Nematic Liquid Crystal Droplets Sophie Ettinger, Angel Martinez, Alexis De la Cotte, Peter Collings, Arjun G Yodh We study the structural transition of nematic liquid crystal (NLC) droplets with homeotropic anchoring in a uniform magnetic field. Confining NLC in droplets creates competition between surface anchoring energy and bulk elasticity, giving rise to distortions and defects. The effects of an electric field on the equilibrium director conformation of NLC droplets are well known, but studies using a magnetic field are scarcer due to the low magnetic susceptibility of most NLCs. We have developed a variable magnet mounted on a polarized microscope that can deliver up to 0.5T of uniform field. With this mechanism, we study the stability of hedgehog defects and the resulting Fréedericksz transition in NLC droplets. We confirm, as predicted theoretically, the formation of a ring defect whose radius increases with field strength as the director approaches a uniformly aligned state. We establish stability diagrams for NLC droplets of various radii and conduct comparative analysis of experimental and calculated threshold fields. Overall, this project aims to elucidate the director configurations of NLCs in confined geometries and to explore their bulk response to external magnetic fields. |
Monday, March 4, 2019 1:39PM - 1:51PM |
B30.00013: Liquid Crystals and the Optical Theorem Xi Chen, Noel Anthony Clark
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Monday, March 4, 2019 1:51PM - 2:03PM |
B30.00014: WITHDRAWN ABSTRACT
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Monday, March 4, 2019 2:03PM - 2:15PM |
B30.00015: Interpretation of saddle-splay and the Oseen-Frank free energy Jonathan Selinger In this talk, we re-examine the oldest question in liquid-crystal physics: What are the elastic modes of a nematic liquid crystal? For this analysis, we use a recent mathematical construction [1], which breaks the director gradient tensor into four distinct types of mathematical objects. Based on this construction, we suggest an interpretation of saddle-splay as bulk rather than surface elasticity. This interpretation leads to an alternative way to think about several previous results in liquid-crystal physics, including: (1) free energy balance between cholesteric and blue phases, (2) director deformations in hybrid-aligned-nematic cells, (3) spontaneous twist of achiral liquid crystals confined in a torus or a cylinder, and (4) curvature of smectic layers. |
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