Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G18: Focus Session: Liquid Crystals, Nano to Meso Scale Structure in Ordered Matter and Liquid Crystal II: Mostly Smectic and Chromonics |
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Sponsoring Units: DCMP GSNP DPOLY Chair: Luz J. Martinez-Miranda, University of Maryland, College Park Room: 403 |
Tuesday, March 4, 2014 11:15AM - 11:27AM |
G18.00001: Diastereomeric domains formed by chiral liquid crystals confined in a network of helical nanofilaments Michael Tuchband, Dong Chen, Balazs Horanyi, Eva Korblova, David Walba, Joseph Maclennan, Matthew Glaser, Noel Clark Mixtures of the bent-core liquid crystal material NOBOW with guest mesogens are well dispersed in the isotropic phase. Upon cooling, the NOBOW forms B4 helical nanofilaments which often nucleate and phase-separate directly from the isotropic melt, forming locally homochiral dendritic networks which act as a porous medium of large internal area. The guest material is then confined to the nanoscale interstitial volumes between the twisted filaments. A typical cell contains a conglomerate of independently nucleated left- and right-handed B4 domains many tens of microns across. Polarized optical microscopy reveals that chiral guest liquid crystal materials with a specific twist of the director form optically distinguishable diastereomeric domains in the left- and right-handed chiral domains. Due to the different twist environments of the pores in the left- and right-handed helical nanofilament networks, the molecular arrangements of chiral guest material and the corresponding changes of birefringence in the left- and right-handed chiral domains differ as the chiral guest transitions from isotropic to cholesteric, and then to smectic. [Preview Abstract] |
Tuesday, March 4, 2014 11:27AM - 11:39AM |
G18.00002: Effective theory and simulations of Smectic-A liquid crystals Danilo Liarte, Matthew Bierbaum, Muxin Zhang, Brian Leahy, Itai Cohen, James Sethna We present simulation results of focal conic structures in smectics-A. Smectic-A is a liquid-crystalline state of matter, with long-range orientational order, and a layered structure with liquid-like order within each layer. In experiments it exhibits striking focal conic domains - defect structures forming beautiful ellipses and hyperbolas. We derive dynamical equations for a vector field that is parallel to the layer normal, and whose size is related to the compression of the layers. In our simulations, focal conic structures spontaneously emerge from random initial configurations, and are characterized by several visualization tools that we developed. We study both coarsening and the effects of shear stress in this system, which are compared with experiments performed in Cornell. We also discuss generalizations to include the dynamics of dislocations. [Preview Abstract] |
Tuesday, March 4, 2014 11:39AM - 11:51AM |
G18.00003: Field-Induced Alignment of Polar Bent-Ccore Smectic A Liquid Crystals Yongqiang Shen, Lisa Goodhew, Renfan Shao, Joseph Maclennan, Noel Clark, Per Rudquist The SmAP$_{\mathrm{F}}$ phase is a promising phase modulator mode. To use the SmAP$_{\mathrm{F}}$ materials for applications, we need to obtain uniform, large-area alignment of the samples. However, bent-core liquid crystals are notoriously difficult to align with conventional surface treatment methods because most of them have no nematic phase. We have developed a powerful, new method using in-plane applied electric fields that allows us to create a perfect bookshelf alignment of orthogonal bent-core smectics. By using an interdigitated, finger-like electrode arrangement on one of the cell surfaces, we can align the materials by applying in-plane electric fields. This stripe geometry, which produces curved field lines, allows for only one smectic layer orientation, normal both to the cell walls and to the finger electrodes. After alignment, the cell can be operated in the conventional way by connecting the finger electrodes together to make one effective electrode, opposing continuous, common electrode on the opposite side of the cell. This alignment method opens up the use of these materials in perfectly aligned cells for both amplitude and phase-only modulation applications. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G18.00004: Rich Variety of Smectic Phases in an Achiral Bent-Core Liquid Crystal Renfan Shao, Cheol Park, Joseph Maclennan, Carlson Tschierske, Noel Clark The mesomorphic properties of an achiral bent-core liquid crystal (PAL30) have been recharacterized using polarizing optical microscopy, electro-optic response measurements and freely-suspended films. We find the phase sequence on cooling to be: I - SmA - SmCAPA' - SmCAPA --SmAPA -- Crystal , and see no evidence of the orthogonal SmAPR and SmAP$\alpha $ phases reported previously [Y.P. Panarin et al., Phys. Rev. Lett. 107,247801,2011]. The tilted SmCAPA' and SmCAPA phases show novel `tiger' pattern and stripe textures in the presence of applied electric field. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G18.00005: Double twist helical nanofilaments in bent-core liquid crystals Cuiyu Zhang, Nicholas Diorio, Oleg D Lavrentovich, Antal Jakli Cryo-TEM observations on 40-150 nm films of four bent-core liquid crystal materials in their helical nanofilament (HNF) phase show that the filaments get deformed near the substrate, and the subsequent arrays of nanofilaments are not parallel, but twisted with respect to each other. The effect can explain the mysterious properties of the HNF materials, such as structural color and ambidextrous optical activity. The observed double twist structure was not expected in the previous models of this phase. Being principally different from the packing of molecules in the twist grain boundary (TGB) and blue (BP) phases, the double-twist structure of HNF expands the rich word of nanostructured organic materials. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G18.00006: Liquid Crystal Phase Transitions and Defects to Sort and Soft-Assemble Microstructures Andrea Rodarte, L.S. Hirst, S. Ghosh The isotropic phase transition of thermotropic nematic liquid crystal (LC) doped with low concentrations of quantum dots (QDs) has previously been used to create ordered clusters of QDs centered at the LC defect points [1]. This process can be exploited to create ordered columns of QD clusters using a micropillar template. In addition, the capping agents on the QDs can be modified to liquid crystal like mesogenic ligands, allowing for better dispersion in the LC host material. At high concentrations of these LC-QDs, we observe a fluid-fluid phase separation in which the functionalized QDs create nematic droplets when dispersed in 4?-Pentyl-4-biphenylcarbonitrile (5CB). Defects and phase separation may be used to sort nanoparticles and create dynamic microstructured assemblies, taking one step closer to soft assembled metamaterials.\\[4pt] [1] A. L. Rodarte, R. J. Pandolfi, S. Ghosh and L. S. Hirst, J. Mat. Chem. C, 1, 5527, 2013. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G18.00007: Light guiding and lasing in Smectic-A liquid crystal fibers Venkata Subba Rao Jampani, Karthik Reddy Peddireddy, Shashi Thutupalli, Christian Bahr, Igor Musevic, Stephan Herminghaus We demonstrate for the first time the optical applications of self-assembled smectic-A liquid crystal fibers in an aqueous micellar medium. These fibers consist of smectic-A layers arranged in a cylindrical fashion so that inevitably a topological line defect exists along the core of the fiber. Light guiding through the fibers and Whispering Gallery Mode (WGM) lasing in a plane perpendicular to the fiber are shown. The light guiding as well as the lasing threshold significantly dependent on the polarization of the excitation beam. The observed threshold for WGM lasing is very low ($\sim$ 75 $\mu$ J/cm$^{2})$ when the pump beam polarization is perpendicular to the direction of the laser dye alignment. Further, these fibers are smooth and flexible and can be manipulated with laser tweezers demonstrating a promising approach for realization of soft photonic circuits. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G18.00008: An upper-bound on the discontinuity at the smectic A-nematic phase transition in octylcyanobiphenyl (8CB): A high-resolution birefringence study Mehmet Can \c{C}etinkaya, Sevtap Yildiz, Haluk Ozbek, Patricia Losada-P\'erez, Jan Leys, Jan Thoen Although the nematic-smectic $A$ ($N$-Sm$A)$ transition in liquid crystals (LCs) has been extensively studied, it is still quite controversial. Most theoretical studies predict that the transition should be of 3-dimensional (3D) XY type. However, the experimental results to date have not established a clear case of 3D \textit{XY} universality. Halperin, Lubensky and Ma (HLM) predicted that the crossover should always make the $N$-Sm$A$ transition first order with very small latent heats. HLM-type first order N-Sm$A$ transitions has been evidenced by ASC data, but inconsistencies remain in reported discontinuity values. Of particular relevance is pure 8CB LC with an estimated HLM contribution substantially smaller than the upper limit for the latent heat from ASC. We carried out high-resolution birefringence measurements near the N-Sm$A $transition of 8CB LC. We find that the Sm$A$-$N $phase transition is continuous. For a possible discontinuity in the $N$ order parameter $S(T)$ at $T_{AN}$ we obtain an upper limit of 0.0002, which is consistent with the ASC latent upper limit and HLM theory. The temperature derivative of $S(T)$ exhibits a power law divergence with a critical exponent that is consistent with $\alpha $ $=$ 0.31 $\pm$ 0.03 obtained from ASC. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G18.00009: Myelin structures formed by thermotropic smectic liquid crystals Karthik Reddy Peddireddy, Pramoda Kumar, Shashi Thutupalli, Stephan Herminghaus, Christian Bahr We report on transient structures, formed by thermotropic smectic-A liquid crystals, resembling the myelin figures of lyotropic lamellar liquid crystals. The thermotropic myelin structures form during the solubilization of a smectic-A droplet in an aqueous phase containing a cationic surfactant at concentrations above the critical micelle concentration. Similar to the lyotropic myelin figures, the thermotropic myelins appear in an optical microscope as flexible tube-like structures growing at the smectic/aqueous interface. Polarizing microscopy and confocal fluorescence microscopy show that the smectic layers are parallel to the tube surface and form a cylindrically bent arrangement around a central line defect in the tube. We study the growth behavior of this new type of myelins and discuss similarities and differences to the classical lyotropic myelin figures. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G18.00010: Thermotropic Liquid Crystalline Side Chain Elastomers David Thomas, Matthew Cardarelli, Peggy Cebe, Badel Mbanga, Timothy Atherton, Antoni Sanchez-Ferrer Nematic Liquid Crystal Elastomers (NLCE) are lightly cross-linked polymeric materials that exhibit rubber elasticity and liquid-crystalline orientational order. We investigated the thermal response and microstructure of side-chain NLCEs using real-time synchrotron wide-angle X-ray scattering (WAXS) and optical ellipsometry. During thermal treatment, the material displayed a highly anisotropic fiber-like diffraction pattern comprising narrow equatorial reflections characteristic of the nematic state. A fully reversible nematic to isotropic transition was observed in WAXS upon heating and cooling. The transition temperature from WAXS was correlated with thermal properties, using differential scanning calorimetry, and with optical properties, using polarizing optical microscopy and transmission ellipsometry. By transmission ellipsometry, with the sample in the low temperature nematic phase, we were able to observe the effect of mechanical stimuli (tensile drawing) on the degree of orientational order. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G18.00011: Lyotropic Chromonic Liquid Crystal Droplets, Faceted and Squeezed Zoey Davidson, Joonwoo Jeong, Matthew Lohr, Peter Collings, Tom Lubensky, Arjun Yodh We report on the structures of lyotropic chromonic liquid crystal (LCLC) droplets of spherical, spherocylinder, and faceted shapes dispersed in a background oil phase. The LCLCs phase varies as a function of the mesogen concentration, which in turn changes the elastic properties and the resultant liquid crystal structure. The various director configurations are investigated by brightfield and polarized optical microscopy and are compared with Jones matrix calculations based on model director configurations. In the nematic phase of the LCLC, the spherical droplets exhibit a twisted bipolar configuration with large chiral symmetry breaking as a result of the small twist elastic modulus. As mesogen concentration increases, the LCLCs enter a columnar phase that energetically prefers a pure bend structure and develops facets at high concentrations. Further, we create spherocylinders to study the effects of droplet shape on defect patterns by squeezing droplets into oil-filled capillaries. The observed director configurations reveal a localization of energy of the director field near the topological defects, and they are understood theoretically to be the result of the LCLC's giant elastic anisotropy. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G18.00012: Phase behavior of chromonic liquid crystal mixtures of Sunset Yellow and Disodium Cromoglycate Akihiro Yamaguchi, Gregory Smith, Youngwoo Yi, Charles Xu, Silvia Biffi, Francesca Serra, Tommaso Bellini, Noel Clark Chromonic liquid crystals (CLCs) are formed when planar molecules dissolved in water stack into rod-like aggregates that can order as liquid crystals. Isotropic, nematic, and M-phases can be observed depending on the degree of molecular orientational and positional order by variation of the CLC concentration. We focused on mixtures of two well-known CLCs, Sunset Yellow, a food dye, and disodium cromoglycate (DSCG), an asthma medication. In order to study the phase behaviors of these mixtures, we observed their textures in glass cells and capillaries using polarized light microscopy. We report here a ternary phase diagram describing the complete phase behavior of the CLC mixtures. We observed a variety of phase behaviors depending on species ratio and concentration. In the isotropic phase, no clear phase separation of the two dyes was observed, while separation did occur in many nematic and M-phase combinations. We will also describe phase observations made using a light spectroscopy and bulk centrifugal partitioning. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G18.00013: Chirality Amplification in Tactoids of Lyotropic Chromonic Liquid Crystals Chenhui Peng, Oleg Lavrentovich We demonstrate an effective chirality amplification based on the long-range forces, extending over the scales of tens of micrometers, much larger than the single molecule (nanometer) scale. The mechanism is rooted in the long-range elastic nature of orientational order in lyotropic chromonic liquid crystals (LCLCs) that represent water solutions of achiral disc-like molecules. Minute quantities of chiral molecules such as amino acid L-alanine and limonene added to the droplets of LCLC lead to chiral amplification characterized by an increase of optical activity by a factor of 10$^{3}$ -- 10$^{4}$. This effect allows one to discriminate and detect the absolute configuration of chiral molecules in an aqueous system, thus opening new possibilities in biosensing and other biological applications. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G18.00014: Orientations of Chromonic Liquid Crystals by Imprinted or Rubbed Polymer Films Youngwoo Yi, Aya Mcguire, Noel Clark A variety of novel alignment effects of chromonic liquid crystal phases of sunset yellow (SSY)/water, disodium cromoglycate (DSCG)/water, and their mixtures by thiol-ene polymer films topographically imprinted with linear channels are observed using polarizing optical microscopy. Nematic DSCG and SSY at low concentration and their nematic mixtures orient with the long axes of stacked chromonic aggregates on average parallel to the channels, that is, with the molecular planes normal to the channel axis. On the contrary, nematic SSY in contact with the rubbed polyimide films orients with the long axes on average in-plane perpendicular to the rubbing direction, arguably, due to a tongue-groove interaction between SSY and the stretched PI chains. Furthermore, multi-stable alignments are observed in SSY solutions of sufficiently high concentration, including preferential in-plane orientation of the long axes of the aggregates parallel to, perpendicular to, and 45$^{\circ}$ rotated from the channels. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G18.00015: Escaped-radial configuration with a twist: lyotropic chromonic liquid crystals confined to cylindrical cavities Joonwoo Jeong, Louis Kang, Zoey S. Davidson, Matthew Lohr, Daniel A. Beller, Randall D. Kamien, Tom C. Lubensky, A.G. Yodh, Peter J. Collings We report new chiral-symmetry-broken configurations of nematic liquid crystals (LCs) confined to cylindrical cavities with a homeotropic boundary condition. In order to relieve high splay deformation in the center of the cylinder with the homeotropic boundary condition, many nematic LCs adopt an escaped-radial configuration where LC directors are radial near the cavity wall but parallel to the cylindrical axis near the center. Interestingly, we find that achiral lyotropic chromonic liquid crystals (LCLCs) having an unusually small twist modulus can have a configuration that is both escaped and twisted radially. Sunset Yellow FCF, a nematic LCLC, is introduced into capillaries coated with a homeotropic alignment layer, and its configurations are investigated by polarized optical microscopy and numerical calculations. Additionally, we discuss other newly observed structures: 1) domain-wall-like defects separating regions of opposite handedness in the twisted- and escaped-radial configuration and 2) another chiral configuration having a double helix of disclination lines along the cylindrical axis. [Preview Abstract] |
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