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2013

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Articles 1291 - 1320 of 11462

Full-Text Articles in Physical Sciences and Mathematics

Tilted Photoalignment Of A Nematic Liquid Crystal Induced By A Magnetic Field, Denis Andrienko, Yuri Kurioz, Yuri Reznikov, Charles Rosenblatt, Rolfe Petschek, Oleg Lavrentovich, Darius Subacius Oct 2013

Tilted Photoalignment Of A Nematic Liquid Crystal Induced By A Magnetic Field, Denis Andrienko, Yuri Kurioz, Yuri Reznikov, Charles Rosenblatt, Rolfe Petschek, Oleg Lavrentovich, Darius Subacius

Oleg Lavrentovich

Nematic liquid crystal cells with polyvinyl cinnamate coated substrates were subjected to ultraviolet light. When this was done in the presence of an oblique magnetic field the photoalignment was found to be temporally and thermally robust, with a large pretilt angle and weak polar anchoring. Moreover, two easy axes with equal and opposite pretilt angle were obtained, such that a magnetic field could switch the director from one easy axis to the other. (C) 1998 American Institute of Physics.

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Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli Oct 2013

Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli

Oleg Lavrentovich

We present the first observations of dc electric-field-induced rotational motion of finite particles in liquid crystals. We show that the electrorotation is essentially identical to the well-known Quincke rotation, which in liquid crystals triggers an additional translational motion at higher fields. In the smectic phase the translational motion is confined to the two-dimensional geometry of smectic layers, in contrast to the isotropic and nematic phases, where the particles can move in all three dimensions. We demonstrate that by a proper analysis of the electrorotation, one can determine the in-plane viscosity of smectic liquid crystals. This method needs only a small …

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Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2013

Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich

Oleg Lavrentovich

We report on the optical properties of the nematic (N) phase formed by lyotropic chromonic liquid crystals (LCLCs) in well aligned planar samples. LCLCs belong to a broad class of materials formed by one-dimensional molecular self-assembly and are similar to other systems such as “living polymers” and “wormlike micelles.” We study three water soluble LCLC forming materials: disodium chromoglycate, a derivative of indanthrone called Blue 27, and a derivative of perylene called Violet 20. The individual molecules have a planklike shape and assemble into rodlike aggregates that form the N phase once the concentration exceeds about 0.1M. The uniform surface …

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Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2013

Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich

Oleg Lavrentovich

We study electric-field-induced dynamics of colloids in a nematic cell, experimentally and by computer simulations. Solid particles in the nematic bulk create director distortions of dipolar type. Elastic repulsion from the walls keeps the particles in the middle of cell. The ac electric field reorients the dipoles and lifts them to top or bottom, depending on dipole orientation. Once near the walls, the colloids are carried along two antiparallel horizontal directions by nematic backflow. Computer simulations of the backflow agree with the experiment.

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Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich Oct 2013

Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich

Oleg Lavrentovich

The surface alignment of lyotropic chromonic liquid crystals can not only be planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is discontinuous and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation.

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Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich Oct 2013

Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich

Oleg Lavrentovich

We describe director distortions in the nematic liquid crystal (LC) caused by a spherical particle with tangential surface orientation of the director and show that light transmittance through the distorted region is a steep function of the particle's size. The effect allows us to propose a real-time microbial sensor based on a nontoxic lyotropic chromonic LC (LCLC) that detects and amplifies the presence of immune complexes. A cassette is filled with LCLC, antibody, and antigen-bearing particles. Small and isolated particles cause no macroscopic distortions of the LCLC. Upon antibody-antigen binding, the growing immune complexes distort the director and cause detectable …

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Directed Vertical Alignment Liquid Crystal Display With Fast Switching, Mingxia Gu, Ivan I. Smalyukh, Oleg Lavrentovich Oct 2013

Directed Vertical Alignment Liquid Crystal Display With Fast Switching, Mingxia Gu, Ivan I. Smalyukh, Oleg Lavrentovich

Oleg Lavrentovich

We describe a directed vertical alignment (VA) display mode based on a nematic liquid crystal (LC) doped with a chiral dopant and confined between two substrates, one of which is pretreated, say, by unidirectional rubbing or photoalignment. The design allows one to eliminate umbilical defects that appear during switching of the conventional VA cells and thus to obtain better contrast. Switching is similar to 30% faster than for VA cells when optimized concentration of a chiral dopant is added and LC molecules at one of the substrates are slightly tilted from the cell normal due to the unidirectional surface treatment.

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Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2013

Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich

Oleg Lavrentovich

We report on a thermodielectric bistability in dual frequency nematic liquid crystals (LCs) caused by the anisotropic nature of dielectric heating and director reorientation in an electric field. The bistability is a result of the positive feedback loop: director reorientation -> anisotropic dielectric heating -> dielectric anisotrophy -> director reorientation. We demonstrate both experimentally and theoretically that two states with different temperature and director orientation, namely, a cold planar state and a hot homeotropic state coexist in a LC cell for a certain frequency and amplitude range of the applied voltage.

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Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni Oct 2013

Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni

Oleg Lavrentovich

Monte Carlo (MC) simulations based exclusively on nearest-neighbor intermolecular interactions reveal the existence of stable long-range deformations and topological defects in a thin nematic film confined between two surfaces with antagonistic (normal and tangential) molecular orientations. Thus the MC technique allows one to describe a delicate balance of bulk elasticity and surface energy usually treated only with macroscopic theories.

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Polarization-Controlled Ohmic To Schottky Transition At A Metal/Ferroelectric Interface, Xiaohui Liu, Yong Wang, John D. Burton, Evgeny Y. Tsymbal Oct 2013

Polarization-Controlled Ohmic To Schottky Transition At A Metal/Ferroelectric Interface, Xiaohui Liu, Yong Wang, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

Ferroelectric polar displacements have recently been observed in conducting electron-doped BaTiO3 (n-BTO). The coexistence of a ferroelectric phase and conductivity opens the door to new functionalities that may provide a unique route for novel device applications. Using first-principles methods and electrostatic modeling, we explore the effect that the switchable polarization of n-BTO has on the electronic properties of the SrRuO3/n-BTO (001) interface. Ferroelectric polarization controls the accumulation or depletion of electron charge at the interface, and the associated bending of the n-BTO conduction band determines the transport regime across the interface. The …

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Contributions To Pion Decay From Lorentz Violation In The Weak Sector, Brett David Altschul Oct 2013

Contributions To Pion Decay From Lorentz Violation In The Weak Sector, Brett David Altschul

Faculty Publications

Lorentz violation in the weak sector would affect the β-decay lifetimes of pions. The decay amplitude may be rendered anisotropic, but only an isotropic violation of boost invariance can affect the net lifetime in the center-of-mass frame. However, since the rest frames of the pions that produce the NuMI neutrino beam at Fermilab vary with the rotation of the Earth, it is possible to constrain anisotropic Lorentz violation using prior analyses of sidereal variations in the event rate at the MINOS near detector. The resulting bounds on weak-sector Lorentz violation are at the 10−4 level, a substantial improvement over …

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Extending Positive Class Results Across Multiple Instructors And Multiple Classes Of Modeling Instruction, Eric Brewe, Adrienne Traxler, Jorge De La Garza, Laird Kramer Oct 2013

Extending Positive Class Results Across Multiple Instructors And Multiple Classes Of Modeling Instruction, Eric Brewe, Adrienne Traxler, Jorge De La Garza, Laird Kramer

Department of Physics

We report on a multiyear study of student attitudes measured with the Colorado Learning Attitudes about Science Survey in calculus-based introductory physics taught with the Modeling Instruction curriculum. We find that five of six instructors and eight of nine sections using Modeling Instruction showed significantly improved attitudes from pre- to postcourse. Cohen’s d effect sizes range from 0.08 to 0.95 for individual instructors. The average effect was d=0.45, with a 95% confidence interval of (0.26–0.64). These results build on previously published results showing positive shifts in attitudes from Modeling Instruction classes. We interpret these data in light of other published …

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Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli Oct 2013

Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli

Antal Jakli

Recently soft fiber mats electrospun from solutions of Barium Titanate (BT) ferroelectric ceramics particles and polylactic acid (PLA) were found to have large (d(33) similar to 1 nm/V) converse piezoelectric signals offering a myriad of applications ranging from active implants to smart textiles. Here, we report direct piezoelectric measurements (electric signals due to mechanical stress) of the BT/PLA composite fiber mats at several BT concentrations. A homemade testing apparatus provided AC stresses in the 50 Hz-1.5 kHz-frequency range. The piezoelectric constant d(33) similar to 0.5 nC/N and the compression modulus Y similar to 10(4)-10(5) Pa found are in agreement with …

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Glass Forming Banana-Shaped Compounds: Vitrified Liquid Crystal States, S. Rauch, C. Selbmann, P. Bault, Hans Sawade, G. Heppke, O. Morales-Saavedra, M. Y. M. Huang, Antal Jákli Oct 2013

Glass Forming Banana-Shaped Compounds: Vitrified Liquid Crystal States, S. Rauch, C. Selbmann, P. Bault, Hans Sawade, G. Heppke, O. Morales-Saavedra, M. Y. M. Huang, Antal Jákli

Antal Jakli

The synthesis and physical properties, in particular electro-optic switching behavior, of 3-chloro-biphenyl-3('),4-bis{4-[4-(3,7-dimethyloctyloxy)-phenyliminomethyl]} benzoate are reported. The compound exhibits an antiferroelectric tilted smectic liquid crystalline phase (Sm-CP) in a broad temperature range. Below 20 degreesC the sample goes over to a glassy state and no crystallization appeares down to -50 degreesC. It is observed that below the glass transition temperature both achiral and chiral structures of the Sm-CP phase can be frozen. Each of them can have three polarization states (two ferroelectric and one antiferroelectric), thus giving six different vitrified textures. This enables atomic force microscopy studies of the different liquid …

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Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. R. Kim, Liang-Chy Chien, A. Saupe Oct 2013

Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. R. Kim, Liang-Chy Chien, A. Saupe

Antal Jakli

Polymer dispersions were made by photoinduced polymerization of 4,4'-bisacryloyl-biphenyl in liquid crystal 4-4'-cyano pentyl biphenyl as nematic solvent. Samples were prepared with 0.5, 1, and 1.5 wt % monomer. The polymerization was done in the isotropic phase. The rotational viscosities of the two lower concentration samples increased only moderately after UV curing (3 mW/cm2, 25 min). The 1.5 wt % sample gave under the same condition a nematic with a fairly rigid anisotropic network that did not realign in magnetic field up to 20 kG. We estimate that the mesh size of the network was in the order of 1 …

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Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Oct 2013

Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson

Antal Jakli

We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.

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Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli Oct 2013

Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli

Antal Jakli

We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial …

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Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli Oct 2013

Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli

Antal Jakli

We demonstrate optical waveguiding in recently discovered free-standing bent-core liquid-crystal filaments. The bent-core liquid-crystal molecules in air self-assemble into a cylindrical geometry that is "solidlike" along the radial direction of the filament and liquid in the axial direction of the filament. These filaments are unique not only because they are fluids, but also because they are anisotropic. For this reason, their waveguiding properties not predictable need to be characterized. The light power transmitted through the filament was found to be independent of temperature from 180 degrees C to near room temperature. Initial defects of newly pulled filaments were found to …

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Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli Oct 2013

Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli

Antal Jakli

We found that the optically isotropic (I-M) mesophase observed recently below the nematic phase of the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy)benzoate] shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the I-M phase is composed of interconnected orthoconic racemic smectic (Sm-CaPF) nanodomains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass-in particular, we observed that the relaxation back to the nonpoled structure follows a similar, inverse logarithmic …

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Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli Oct 2013

Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli

Antal Jakli

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C*(SmC*) to AF1 phase transition (around 103.0 °C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmCA*) and AF2 (Sm …

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Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien Oct 2013

Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien

Antal Jakli

The transfer of chirality from nonchiral polymer networks to the racemic B2 phase of nonchiral banana-shaped molecules is demonstrated. This corresponds to the transfer of chirality from an achiral material to another achiral material. There are two levels of chirality transfers. (a) On a microscopic level the presence of a polymer network (chiral or nonchiral) favors a chiral state over a thermodynamically stable racemic state due to the inversion symmetry breaking at the polymer-liquid crystal interfaces. (b) A macroscopically chiral (enantimerically enriched) sample can be produced if the polymer network has a helical structure, and/or contains chemically chiral groups. The …

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Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli Oct 2013

Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli

Antal Jakli

Electro-optical, calorimetric, x-ray, and dielectric measurements are reported on a mixture containing a bent-core liquid crystal 4-chloro-1,3-phenylinebis [4-(4-n-tetradecyloxyphenyliminomethyl) benzoate] mixed with the nonpolar solvent n-hexadecane (HEX). It is observed that the addition of HEX depresses the isotropic-to-smectic phase transition temperature, but the crystallization temperature does not change considerably. Instead, the texture of the crystalline phase changes and, at sufficiently high concentrations of HEX (>20 wt %), an optically isotropic phase appears. Above 40 wt % HEX concentrations, the mesophase completely disappears and a direct isotropic solid-to-isotropic liquid transition takes place. At increasing HEX concentration, the transition enthalpies, the layer …

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Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Oct 2013

Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Antal Jakli

Flexoelectricity is a unique property of liquid crystals; it is a linear coupling between electric polarizations and bend and/or splay distortions of the direction of average molecular orientation. Recently it was shown [J. Harden et al., Phys. Rev. Lett. 97, 157802 (2006)] that the bend flexoelectric coefficient in bent-core nematic liquid crystals can be three orders of magnitude higher than the effect with calamitic (rod-shaped) molecular shape. Here we report the converse of the flexoelectric effect: An electric field applied across a bent-core liquid crystal sandwiched between thin flexible substrates produces a director distortion which is manifested as a polarity-dependent …

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Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair Oct 2013

Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair

Antal Jakli

Although the liquid-crystal research is well established in science, there are newly emerging exciting systems, that deserve extensive basic studies. One of these areas is the research of the bent-shaped molecules (so-called "banana liquid crystals"), which have delicate chirality and polarity properties. In this paper we show that these materials also have very unusual rheological features, such as the formation of stable fluid fibers and bridges. Under electric fields, these objects present striking mechanical effects, such as horizontal and transversal vibrations. Studies indicate that the research of banana-liquid-crystal fibers may lead to new type of artificial muscle systems.

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Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy Oct 2013

Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy

Antal Jakli

We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (similar to 1 mW/mm(2)) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis isomer. The …

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Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Oct 2013

Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Antal Jakli

We have found that bent-core liquid crystalline materials show exceptionally large intrinsic flow birefringence in their isotropic liquid phase. This effect is more than 100 times larger than typical values measured for low molecular weight liquid crystals. The specific flow birefringence (i.e., normalized by the flow viscosity) is an order of magnitude larger than in both side-chain polymeric as well as low molecular weight liquid crystals. We propose that this large enhancement for bent-core compounds may be attributed to nanoscale smecticlike clusters that persist above the nematic-isotropic transition temperature, and shear align under shear flow; however, this mechanism has not …

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Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke Oct 2013

Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke

Antal Jakli

The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-C-G phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C-1 symmetry). The observations suggest that the phase tentatively labeled as B-7 is identical with the Sm-C-G phase.

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Imprinting The Quasi Bookshelf Texture Of A Ferroelectric Liquid Crystal Into Nano-Scaled Polymer Fibrils, S. H. Kim, S. Suresh, Liang-Chy Chien Oct 2013

Imprinting The Quasi Bookshelf Texture Of A Ferroelectric Liquid Crystal Into Nano-Scaled Polymer Fibrils, S. H. Kim, S. Suresh, Liang-Chy Chien

Liang-Chy Chien

Polymer-stabilized ferroelectric liquid crystals (PSFLCs) are made by photopolymerizing 3% reactive mesogenic monomer on a quasi bookshelf texture of a ferroelectric liquid crystal (FLC). We observe the formation of nano-scaled polymer fibrils templated by the two dimensionally ordered host. The polymer fibrils capture the orientation of the host with thin polymer fibrils interweaving the smectic layers. The SEM study highlights the difference in morphology of the polymer fibrils depending on polymerization conditions; that is, polymerizing with or without the presence of an electric field. The polymer networks suppress the cone of rotation of FLC and thus, facilitate the switching and …

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Three-Dimensional Orientational Order In The Bulk And On The Surface Of Polymer Films And Its Effect On Liquid-Crystal Alignment, O. V. Yaroshchuk, Yu. Zakrevskyy, Satyendra Kumar, J. Kelly, Liang-Chy Chien, J. Lindau Oct 2013

Three-Dimensional Orientational Order In The Bulk And On The Surface Of Polymer Films And Its Effect On Liquid-Crystal Alignment, O. V. Yaroshchuk, Yu. Zakrevskyy, Satyendra Kumar, J. Kelly, Liang-Chy Chien, J. Lindau

Liang-Chy Chien

The correlation between orientation ordering of polymer chains in the bulk of polymer film and at the polymer-liquid-crystal (LC) interface has been studied to determine it's role in LC alignment. The bulk and surface ordering of polymer were investigated by null ellipsometry and x-ray reflectivity, respectively. Two kinds of liquid-crystalline polymers were used; side-chain azopolymers with azochromophores containing hydrophobic OC(4)H(9) alkyl chain (P1) and strongly polar NO(2) group (P2) as the end substituents. The uniaxial tilt orientation of azochromophores in the films of both polymers was induced by the oblique irradiation with unpolarized UV light. The two polymers exhibit similar …

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Optical Studies Of The Liquid Crystal B2 Phase Formed By Banana-Shaped Molecules, D. A. Olson, M. Veum, A. Cady, M. V. D'Agostino, P. M. Johnson, H. T. Nguyen, Liang-Chy Chien, C. C. Huang Oct 2013

Optical Studies Of The Liquid Crystal B2 Phase Formed By Banana-Shaped Molecules, D. A. Olson, M. Veum, A. Cady, M. V. D'Agostino, P. M. Johnson, H. T. Nguyen, Liang-Chy Chien, C. C. Huang

Liang-Chy Chien

Null-transmission ellipsometry and depolarized light microscopy have been performed on free-standing films of three achiral banana-shaped compounds in the B2 phase. Our results support a two-layer unit cell previously proposed to explain the observed antiferroelectricity in thin films and bulk samples. We have studied thicker films than previously reported and have found no deviations in the film structure from the earlier findings. Moreover, we can determine the layer spacing, the molecular tilt from the layer normal, and the three principal indices of refraction in the molecular reference frame.

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