Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J9: Liquid Crystals: Nematics, Lyotropics and Vesicles |
Hide Abstracts |
Sponsoring Units: DFD Chair: Satyendra Kumar, Kent State University Room: D220 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J9.00001: Dynamics of chiral liquid-crystal films driven by water transport Jonathan V. Selinger, Lena M. Lopatina In previous experimental and theoretical research, Tabe and Yokoyama investigated Langmuir monolayers of chiral molecules on the surface of water, and found that evaporation of water induces collective precession of the molecular orientation [1]. More recently, they have found a similar effect in freely suspended films of chiral smectic liquid crystals, but with one new feature: the molecular rotation is accompanied by large- scale flow of the molecules, indicating a strong coupling between orientation and flow. To model the coupled rotation and flow driven by water transport, we construct the Lagrangian and Rayleigh dissipation function appropriate for a film in the smectic-A or smectic-C phase, derive the equations of motion, and solve these equations in geometries corresponding to the experiments. In particular, we calculate the flow patterns in terms of the viscosity coefficients of the liquid-crystal films, in order to understand the mechanisms that control this dynamic behavior. The theoretical predictions are compared with experimental results, and with related work on granular materials [2]. \\[4pt] [1] Y. Tabe and H. Yokoyama, Nature Mat. 2, 806 (2003).\\[0pt] [2] J.-C. Tsai, F. Ye, J. Rodriguez, J. P. Gollub, and T. C. Lubensky, Phys. Rev. Lett. 94, 214301 (2005). [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J9.00002: Linear aggregation and liquid-crystalline order: comparison of Monte Carlo simulation and analytic theory Tatiana Kuriabova, M.D. Betterton, Matthew A. Glaser Many soft-matter and biophysical systems are composed of monomers that reversibly assemble into rod-like aggregates. The aggregates can then order into liquid-crystal phases if the density is high enough, and liquid-crystal ordering promotes increased growth of aggregates. Systems that display coupled aggregation and liquid-crystal ordering include wormlike micelles, chromonic liquid crystals, DNA and RNA, and protein polymers and fibrils. Coarse-grained molecular models that capture key features of coupled aggregation and liquid-crystal ordering common to many different systems are lacking; in particular, the roles of monomer aspect ratio and aggregate flexibility are not well understood. We study a system of sticky cylinders that interact primarily by hard-core interactions but can stack and bind end to end. We use Monte Carlo simulations and analytic theory. We present results for several different cylinder aspect ratios and a range of end-to-end binding energies. The phase diagrams are qualitatively similar to those of chromonic liquid crystals, with an isotropic-nematic-columnar triple point. Our analytic theory shows improvement compared to previous theory in quantitatively predicting the I--N transition for relatively stiff aggregates, but requires a better treatment of aggregate flexibility. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J9.00003: Modeling the Kerr effect in polymer-disordered liquid crystals Lena M. Lopatina, Jonathan V. Selinger In the Kerr effect, an electric field applied to an optically isotropic material induces orientational order and hence induces optical birefringence. Recently, many investigators have used the Kerr effect to develop liquid-crystal displays and other electro-optic devices that can operate at high speed and with no need for aligning substrates. This application requires a large and fairly temperature-independent Kerr coefficient. One approach to achieve this goal is by using liquid-crystal blue phases, perhaps with polymer stabilization. As an alternative approach, D.-K. Yang has suggested using a nematic phase within a disordered polymer network. This structure would be disordered and optically isotropic in the absence of a field, but it would develop order and birefringence under an applied field. To assess this approach, we perform Monte Carlo simulations of a nematic liquid crystal in a disordered polymer network, and calculate the response to an applied field. We compare the results with analytic studies of liquid crystals under quenched disorder and with experiments. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:03PM |
J9.00004: A nonlocal model of inhomogeneous nematic liquid crystals Peter Palffy-Muhoray, Xiaoyu Zheng, Roland Ennis The free energy cost of spatial inhomogeneities in nematic liquid crystals is usually described in terms of gradients of the director field or of the order parameter tensor. The origins of such gradient expansions are not clear; they can also lead to ill-posedness of the variational problem of minimizing the free energy. We propose a simple nonlocal form of the single particle potential from which the free energy may be constructed. Our model reduces to the Maier-Saupe form for homogenous systems, but describes inhomogenous systems in general. We demonstrate the validity of the model by using it to describe the electric field induced Freedericksz transition. We discuss the connection between our non-local model and gradient expansions. [Preview Abstract] |
Tuesday, March 22, 2011 12:03PM - 12:15PM |
J9.00005: Freely Suspended Nematic Films Wilder Iglesias, Jeffrey Choi, Elizabeth K. Mann, Antal Jakli Using one of the most commonly studied synthetic molecule, 4-Cyano-4'-pentylbiphenyl (5CB), we were able to pull freely suspended membranes of different thicknesses into circular frames of up to 20mm diameter. Films pulled this way were distorted using a speaker, while a laser light was shone onto them for studying the far field reflection and learn about resonant frequency modes and subtract valuable information about the viscoelastic terms that hold the membrane stable. [Preview Abstract] |
Tuesday, March 22, 2011 12:15PM - 12:27PM |
J9.00006: Fluctuation Modes of a Bent-Core Nematic Liquid Crystal Madhabi Majumdar, S. Chakraborty, B. Senyuk, O.D. Lavrentovich, James T. Gleeson, Antal Jakli, Samuel Sprunt We present a dynamic light scattering study of the bent-core nematic liquid crystal compound \textit{DT6Py6E6. }We utilize a ``dark'' scattering geometry, which allows us to search for fluctuation modes that are not purely associated with the uniaxial director. Indeed, we observe two modes (hydrodynamic and non-hydrodynamic) in addition to the expected twist-bend director mode. We present a model for the additional modes based on fluctuations of the biaxial order parameter, which leads to an estimate of 10-100 nm for the correlation length associated with these fluctuations. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J9.00007: Three dielectric constants and orientation order parameters in nematic mesophases Hyung Guen Yoon, Seung Yeon Jeong, Satyendra Kumar, Min Sang Park, Jung Ok Park, M. Srinivasarao, Sung Tae Shin Temperature dependence of the three components $\varepsilon _{1}$, $\varepsilon _{2}$, and $\varepsilon _{3}$ of dielectric constant and orientation order parameters in the nematic phase of mesogens with rod, banana, and zero-order dendritic shape were measured using the in-plane and vertical switching geometries, and micro-Raman technique. Results on the well-known uniaxial (N$_{u})$ nematogens, E7 and 5CB, revealed two components $\varepsilon _{1~}$=~$\varepsilon _{\vert \vert }$ and $\varepsilon _{2~}$=~$\varepsilon _{3~}$=~$\varepsilon _{\bot }$, as expected. The three dielectric constants were different for two azo substituted (A131 and A103) and an oxadiazole based (ODBP-Ph-C12) bent core mesogens, and a Ge core tetrapode. In some cases, two of the components became the same indicating a loss of biaxiality at temperatures coinciding with the previously reported N$_{u}$ to biaxial nematic transition. This interpretation is substantiated by micro-Raman measurements of the uniaxial and biaxial nematic order parameters. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J9.00008: The interplay between fluctuations in physical structure and power consumption in electroconvecting liquid crystals John Cressman, Zrinka Greguric, Tyrus Berry, Timothy Sauer We will present results from experiments performed on the nematic liquid crystal MBBA. We have made simultaneous measurements of the optical patterns formed in the weakly-driven electroconvective state, as well as the electrical power consumed by the sample. By performing a dimensionality reduction on the optical data we identify the dominant modes in the system and go on to elucidate the role of these modes in the measured power fluctuations. We will conclude by discussing these results in the context of the free energy derived by de Gennes for nematic liquid crystals. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J9.00009: Magneto-optical technique for detecting biaxial nematic phase Tanya Ostapenko, J.T. Gleeson, S.N. Sprunt, A. Jakli There have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase. There have been findings of biaxial order in bent-core nematic liquid crystals; however, there are recent reports that call this into question. One reason for this discrepancy is the difficulty in unambiguously identifying the biaxiality. Based on a previously described electro-optical technique, we have developed a technique that uses magnetic field, thus widening its application to any bent-core nematic material. The field orients the uniaxial director along the optical path length, and we search for birefringence perpendicular to this direction. We expect one of two situations to occur: if the material is uniaxial, the induced phase difference will decrease asymptotically to zero as the field increases. However, if the material is biaxial, the induced phase will extrapolate to a non-zero value. Results on one calamitic liquid crystal show that this method yields the expected result, namely the lack of biaxial nematic phase. We also tested several bent-core nematic liquid crystals and found that none of these materials exhibits a biaxial nematic phase. [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:15PM |
J9.00010: Nonlinear electrophoresis in nematics: Flows and effects of salts Israel Lazo-Martinez, Oleg D. Lavrentovich Electrophoresis (EP) in a nematic liquid crystal (LC) is dramatically different from its isotropic counterpart, as the EP velocity has a component that is quadratic in the applied electric field [1]. Unlike the regular EP velocity that is linear in the field, this component does not vanish in an ac field with a zero time average, which makes the LC EP attractive for applications where the steady flows are needed. EP propulsion is caused by distortion of the LC orientation around the particles that break the fore-aft (or left-right) symmetry, leading towards an imbalance of field-induced flows around the particles. We visualize the flows and measure the EP velocity by recording 3D trajectories of passive tracers suspended in the LC under the fluorescent confocal polarizing microscope. We demonstrate that doping the LC with organic salts increases the EP velocities. The work was supported by NSF DMR 0906751. \\[4pt] [1] O. D. Lavrentovich, I. Lazo, O. P. Pishnyak, Nature 467, 947-950 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 1:15PM - 1:27PM |
J9.00011: Anisotropic Stokes Drag and Dynamic Lift on Cylindrical Colloids in a Nematic Liquid Crystal Joel Rovner, Clayton Lapointe, Daniel Reich, Robert Leheny Unlike isotropic fluids, nematic liquid crystals exhibit a complex assortment of hydrodynamic properties that can strongly depend on the director field and local boundary conditions set by inclusions. To understand further these characteristics, measurements were taken of the Stokes drag on magnetic nanowires suspended in nematic 4-cyano-4'-pentylbiphenyl (5CB). Effective drag viscosities for wires moving perpendicular and parallel to the nematic director were measured and were found to differ by factors of approximately 0.88 to 2.4, depending on the wire orientation and surface anchoring. Additionally, a lift force was observed when wires were forced at an oblique angle to the director resulting in motion divergent from the line of force. The lift was greater for wires with homeotropic anchoring and smaller for wires with longitudinal anchoring, suggesting that the lift force can act as a mechanism for sorting colloidal particles according to their surface chemistry. [Preview Abstract] |
Tuesday, March 22, 2011 1:27PM - 1:39PM |
J9.00012: Morphology and Rheology of the Liquid Crystal-Colloid Composites Lu Zou, Chanjoong Kim Liquid crystal (LC)-colloid composites form aggregates and are arrested in various network structures. We study viscoelastic properties and three-dimensional structure of nematic LC-colloid composites using fluorescence confocal polarized rheoscope and fluorescence microscope. We observe various morphological transformations of the composites when we cool them down below $T_{NI}$ from the high temperature isotropic phase. We find that colloidal particles are self-organized to ferny structures, and that the morphological characteristics of the ferny structures depend on the applied shear rates, the cooling rate, the particle volume fraction and the particle size. This study may offer a new route to form novel colloidal structures using anisotopic fluid, which could not be obtained from isotropic suspensions. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J9.00013: Structural Reorganization of Liquid Crystals Revealled by Fast Scanning Calorimeter Dongshan Zhou, Jing Jiang, Xiaoliang Wang, Gi Xue Liquid crystal glass of 4-Cyano-4'-octylbiphenyl is obtained by rapid cooling with rates over 2000 Kelvin per second (K/s) on the chip calorimeter. The glass can crystallize easily upon heated above its glass transition temperature. Depending on the prior cooling rate and annealing history thereafter, melting-structural reorganization-remelting behavior similar to that of semicrystalline polymer can be observed during subsequent heating. The complex melting behavior is attributed to the transformation of metastable crystal forms formed during annealing or heating induced cold crystallization. Increasing the heating rate ($>$15000 K/s) can suppress the transformation and, additionally, enables us to capture the multiple N-I transition. This implies the coexistence of two different types of nematic states. To avoid above complex structural reorganization, one can anneal the sample at 260K for 2 seconds to get the stable crystal form. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J9.00014: Parity breaking in nematic tactoids of lyotropic chromonic liquid crystals Luana Tortora, Oleg D. Lavrentovich In many colloidal systems, an orientationally ordered nematic phase emerges from the isotropic melt in the form of spindle-like birefringent tactoids. In cases studied so far, the tactoids always reveal a mirror-symmetric non-chiral structure, even when the building units are chiral, as in the case of tobacco mosaic virus [1] and fd virus [2]. We report on parity breaking in the nematic tactoids formed in molecularly non-chiral polymer-crowded solutions of lyotropic chromonic liquid crystals. The effect is manifested by twist of the director and optical activity. Fluorescent confocal polarizing microscopy reveals that the tactoids nucleate at boundaries of cells. We explain the chirality induction by the effect of geometrical anchoring [3] and by increase of the splay elastic constant in condensed nematic regions of crowded solutions.\\[4pt] [1] J. D. Bernal and I. Fankuchen, J. Gen. Physiol. \textbf{25}, 111 (1941);\\[0pt] [2] Z. Dogic, Phys. Rev. Lett. \textbf{91}, 165701 (2003);\\[0pt] [3] O.D. Lavrentovich, Phys. Rev. A15 \textbf{46}, R722 (1992) [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J9.00015: Orientational order and defect structures on curved surfaces Subas Dhakal, Francisco J. Solis, Monica Olvera de la Cruz We study the topological defects in a nematic liquid crystal confined to a surface. Using Monte Carlo simulations, we investigate how the position and number of defects depend on the interaction strength, the shape of the surface and other physical parameters. On a spherical surface, we find that the interaction changes the location of four +1/2 defects initially sitting on a great circle of the sphere to the vertices of a tetrahedron. In deformed spheres, we observe the coalescence of defects into two single +1 defects. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700