Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V57: Self-assembly in Liquid Crystals and other Complex Solvents II |
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Sponsoring Units: GSOFT DBIO DPOLY Chair: Jacinta Conrad, Univ of Houston Room: LACC 518 |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V57.00001: Quantization of bending waves in a living nematic Andrey Sokolov, Mikhail Genkin Living nematic is a realization of an active matter combining a nematic liquid crystal with swimming bacteria. Self-organized bending waves emerge from the initial uniform alignment with a characteristic length controlled by a balance between bacteria activity and anisotropic viscoelasticity of liquid crystal. In this work, we study living nematic confined in a circular track. The wavelengths of the observed waves depend on both bacterial activity and confinement size. In contrast to quasi-infinite systems, in which the wavelength of periodic director instability is a continuous function of bacteria activity, in this work, we only observed instabilities with quantized wavelengths. Transitions between different states associated with different wavelengths are triggered by changes in bacterial activity. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V57.00002: Brownian Dynamics of Colloidal Particles in Lyotropic Chromonic Liquid Crystals Angel Martinez, Peter Collings, Arjun Yodh We employ video microscopy to study Brownian dynamics of colloidal particles suspended in the nematic phase of the lyotropic chromonic liquid crystal , Disodium Chromoglycate, (DSCG). DSCG is water soluble, and its nematic phase is characterized by an unusually small twist elastic constant, which leads to formation of chiral director configurations. The mean-square displacement for polystyrene microspheres moving parallel to the far-field director is sub-diffusive for lag times up to several seconds and then diffusive at longer times. Dynamics perpendicular, by contrast, is slower and never quite becomes diffusive, even after hundreds of seconds of lag time. We also compared the diffusion of spheres inducing energetically distinct director field configurations and found them to be different depending on chirality. We compare our observations to previous diffusion experiments in nematic LCs [1-4], and seek to understand our results using conventional diffusion theory. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V57.00003: Optimizing parameters in co-assembly of magnetic and semiconducting nanoparticles templated by liquid crystal phase transition Mark Bartolo, Jose Amaral, Randy Espinoza, Noah Bessard, Sayantani Ghosh A much sought-after goal in nanofabrication via self-assembled nano-components is creating artificial materials that exhibits multifunctionality and in situ responsiveness to external stimuli. We explore the ensemble behavior of iron oxide magnetic nanoparticles (MNPs) and CdSe/ZnS quantum dots (QDs) when dispersed in electro-optically active liquid crystalline matrix. Prior research has demonstrated an enhancement in the QD emission with a small applied magnetic field, a result of synergistic interactions between nanoparticles. In this work, the phase space is expanded by varying the sizes and relative proportions of QDs and MNPs in the assemblies. The aim is to determine the limits of sensitivity as a function of MNP size while keeping the relative concentration within a narrow range. We use 20 nm, 10 nm and 5 nm MNPs with 6 nm QDs and find that while the emission enhancement is observed for all, the reversibility is absent in the 20 nm MNP co-assembly. Transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal that the co-assemblies have QDs at the center with MNPs dispersed more uniformly, and the rotation of MNPs in an applied field may be the driving mechanism behind the observed effect. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V57.00004: Abstract Withdrawn
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Thursday, March 8, 2018 3:18PM - 3:30PM |
V57.00005: Polar anchoring strength enhancement in a graphene-nematic suspension and its effect on the nematic electro-optic switching Rajratan Basu A small quantity of monolayer graphene flakes is doped in a nematic liquid crystal (LC), and the effective polar anchoring strength coefficient between the LC and the alignment substrate is found to increase by an order of magnitude. The hexagonal pattern of graphene can interact with the LC’s benzene rings via p-p electron stacking, enabling the LC to anchor to the graphene surface homogeneously (i.e. planar anchoring). When the LC cell is filled with the graphene-doped LC, some graphene flakes are preferentially attached to the alignment layer and modify the substrate’s anchoring property. These spontaneously deposited graphene flakes promote planar anchoring at the substrate and the polar anchoring energy at alignment layer is enhanced significantly. The enhanced anchoring energy is found to impact favorably on the electro-optic response of the LC. Additional studies reveal that the nematic electro-optic switching is significantly faster in the LC + graphene hybrid than that of the pure LC. |
Thursday, March 8, 2018 3:30PM - 3:42PM |
V57.00006: Liquid Crystals and Nanoparticles: Convergence of the Smectic A Correlation Length Independent of Concentration Luz Martinez-Miranda, Eduardo Soto-Bustamante, Patricio Romero-Hasler, Ariel Meneses-Franco We performed an X-ray study as a function of temperature on the monomer M6R8 with a 7, 15 and 30% wt of TiO2 nanoparticles and compared it to the 0% or pure monomer. The pure monomer has a phase sequence of Crystal –sm-C (54.7C) – sm-A (80C)-isotropic (97.0C). We have found that this phase sequence is preserved and there is not a large variation in temperature independent of the concentration. There is a peak associated with the interaction between the monomer and the nanoparticle that appears as a shoulder peak to the monomer peak. There is a large variation in this peak that characterizes the sm-C for all concentrations but not the peak that characterizes the sm-A. The correlation length for the sm-A peak converges toward the same value, independent of concentration. There is also a lower angle peak that appears when we add the nanoparticle, but whose correlation length also converges towards the sm-A phase, independent of the concentration. We conclude that independent of the concentration with which the liquid crystal is doped there is a terminal concentration that stays with the liquid crystal. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V57.00007: Phase behavior and magneto-optic response of lyotropic liquid crystals with ferromagnetic nanoplates Min Shuai, Hayden Dodge, Gregory Smith, Chenhui Zhu, Joseph MacLennan, Matthew Glaser, Noel Clark As a recently discovered soft mater system, ferromagnetic lyotropic liquid crystals offers great potential for various applications [Nature Communications, 7: 10394, 2016]. Here, we expand the potential applications of magnetic colloids by combining disk-shaped ferromagnetic nanoparticles with nonmagnetic nanosheets. We find that by doping with low concentration of ferromagnetic barium hexaferrite nanoplates, the magnetic susceptibility of suspensions of colloidal nanosheets, in this case exfoliated monolayer zirconium phosphate, is largely enhanced. Colloidal mixtures of these two kinds of disk-shaped nanoparticles form a series of stable mesophases, among which the paramagnetic nematic liquid crystal phase shows Hertz-scale magneto-optic response to applied fields. Polarized optical microscopy and synchrotron X-ray scattering are used to probe the ordering and dynamic response of this new colloidal system with and without applied magnetic fields. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V57.00008: Effects of Chiral Dopants on Doubly Twisted Configurations of Lyotropic Chromonic Liquid Crystals in a Cylindrical Cavity Jonghee Eun, Joonwoo Jeong Confined lyotropic chromonic liquid crystals (LCLCs) often show chiral director configurations despite the absence of intrinsic chirality at the molecular level. For example, nematic LCLCs in a cylindrical cavity with a degenerate planar anchoring exhibit doubly twisted (DT) configurations because of unprecedentedly large saddle-splay-to-twist elasticity ratio. In this work, we investigate how chiral dopants affect this chiral symmetry breaking of LCLCs focusing on the DT configurations in a capillary. We find that, in a cylindrical confinement, the cholesteric LCLCs with a minuscule amount of chiral dopants still show the DT configuration with domains of different handednesses and defects between them. But it becomes homochiral when the dopant concentration is high enough. We characterize these cholesteric DT configurations by optically measured twist angles and provide a simple theoretical model on the energetics of cholesteric DT configurations. Finally, we observe the enantiomeric excess of chiral dopants influence the director configuration when dopants of two different handednesses are mixed. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V57.00009: Chiral configurations from racemic lyotropic polymer liquid crystals under cylindrical confinement. Rui Chang, Elsa Reichmanis, Jung Park, Mohan Srinivasarao The emergence of chiral structures from achiral molecules inspires scientists about the origin of chirality in nature. Recently, chiral configurations have been reported on confining achiral lyotropic chromonic liquid crystals and micellar liquid crystals to cylindrical and spherical geometries. Emergence of chirality in these systems has been attributed to small twist elastic constant and curved surfaces of confinement. In this work, we studied a racemic lyotropic polymer liquid crystal in cylindrical capillaries. Although the polymer liquid crystal is composed of much longer molecules, it also has a small twist elastic constant and exhibits the same chiral configurations as chromonics and micelles. Additionally, we exploited the chiral configurations to estimate the saddle-splay elastic constant and anchoring strength on the surface. Our work suggests that the emergence of chirality widely exists for all types of achiral lyotropic liquid crystals. And the small twist elastic constant seems to be a common property of all lyotropics. This generalization stimulates fundamental understanding about configurational and elastic behavior of lyotropic system. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V57.00010: Polymer networks as templates for large-scale defect arrays in liquid crystals MinSu Kim, Francesca Serra We utilize crosslinked liquid crystalline polymers to drive the assembly of nematic, smectic and cholesteric liquid crystals (LCs) into large-scale, regular arrays of topological point defects. The polymer network is created by dispersing a mesogenic monomer (RM257) in nematic LC. We utilize the method discovered by Orihara and colleagues [1] to fabricate regular arrays of umbilical defects by applying an electric field to a homeotropic cell containing nematic LC with negative dielectric anisotropy. We modify this method using patterned, partially etched electrodes with different symmetries, which enable the formation of regular arrays of defects over the length-scale of several millimeters. We study the structure of the defect array as a function of the geometry of the patterned electrodes. The polymer network, which is crosslinked while an electric field is applied, can then be emptied and re-filled with nematic, smectic, and cholesteric LCs, to which it imposes its alignment. This strategy allows us to create stable, but tunable optical gratings. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V57.00011: Amplification of chirality of lyotropic chromic liquid crystals confined to capillaries. Sujin Lee, Rui Chang, Elsa Reichmanis, Jung Park, Mohan Srinivasarao In recent years, intensive research has been conducted with the focus on amplification of chirality in the liquid crystalline system for applications including chiral supramolecular assemblies, smart materials, and the development of liquid crystal displays. Lyotropic chromic liquid crystals (LCLC) molecules are achiral, that have plank-like rigid aromatic cores and hydrophilic ionic groups at the peripheries. Upon confinement of LCLCs in cylindrical capillary, the director adopts a doubly twisted director configuration, and possess multi domain with equal probability of both handedness which is separated by Neel walls. In this work, we observed that by adding minute amount of chiral molecules to racemic mixtures, the whole system can be transformed into one type of structural handedness. When we added L-alanine and D-alanine, we can see that the minute amount of these chiral materials broke the parity and dominate the capillaries with left and right handed structure, respectively. The structure and charge of the chiral molecules were also studied. By investigating the effect of various chiral molecules within this LCLCs in capillary system, we expect to understand chirality amplification mechanisms. |
Thursday, March 8, 2018 4:42PM - 4:54PM |
V57.00012: Superior Electro-thermo-optical Properties of Homogeneous Liquid Crystals Aligned on Transparent Carbon Nanotube Sheet Kieu Truong, Ji Huyn Park, MD Asiqur Rahman, Martin Urbanski, Giusy Scalia, Dongseok Suh Highly-aligned carbon nanotube (CNT) sheet is examined as an outstanding alternative alignment layer for liquid crystal display, conventionally consisting of indium tin oxide transparent electrode combined with rubbed polyimide. A single CNT sheet, mechanically drawn from multi-walled CNT forest, is attached on the silane-treated glass substrate, followed by the deposition of an alumina thin film for a better adhesion and a complete insulation. The test liquid crystal (LC) display cell has the LC molecule of 4-Cyano-4'-pentylbiphenyl, sandwiched by the CNT-sheet-on-glass substrates. The thermal–optical characterization under the polarizing microscopy and the LC switching driven by the electric field supports the synergistic effects between aligned CNT bundles and LC molecules. These results present an opportunity to deploy the new alignment layer of CNT sheet for the liquid crystal display application. |
Thursday, March 8, 2018 4:54PM - 5:06PM |
V57.00013: Defects in an Active Nematic Confined to a Toroid Perry Ellis, Alberto Fernandez-Nieves Active materials are driven far from the ground state by the motion of their constituent particles, thereby making them inherently non-equilibrium materials. For an active nematic, this results in a continuous creation and annihilation of ±1/2 defect pairs. Here, we confine an active nematic to the surface of a toroid and focus on how the defect density and defect orientation couple to the curvature of the underlying surface. |
Thursday, March 8, 2018 5:06PM - 5:18PM |
V57.00014: Abstract Withdrawn
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Thursday, March 8, 2018 5:18PM - 5:30PM |
V57.00015: Modifying Hydrogen-Bonded Structures by Physical Vapor Deposition: 4-methyl-3-heptanol Amanda Young-Gonzales, Mark Ediger, Ranko Richert Unlike many glass forming monohydric alcohols the equilibrium state of 4-methyl-3-heptanol (4M3H, Tg =162 K) is believed to be characterized by ring-like hydrogen-bonded structure. As a result, this alcohol is very non-polar and has a low dielectric constant. To test this connection between hydrogen bonded rings and the absence of polarity, we study vapor-deposited films of 4M3H for conditions which are meant to prohibit the formation of supra-molecular structures. Using deposition rates between 0.9 and 6.0 nm/s, we prepared films and measured the dielectric properties via an interdigitated electrode cell. Films deposited at temperatures below Tg show a high dielectric loss upon heating, which decreases by a factor of about 12 by annealing. This change is consistent with a drop of the Kirkwood correlation factor, gK, by a factor of about 10, indicative of changes towards ring-like hydrogen-bonded structures characteristic of the ordinary liquid. We rationalize the high dielectric relaxation amplitude in the vapor deposited glass by suggesting that depositions at low temperature provide insufficient time for molecules to form ring-like supramolecular structures for which dipole moments cancel. |
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