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Articles 1 - 23 of 23

Full-Text Articles in Physics

Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Aug 2012

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

Chemical Physics Publications

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.


Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich Jul 2012

Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich

Chemical Physics Publications

Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twistK2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher thanK2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not ...


Lyotropic Chromonic Liquid Crystal Semiconductors For Water-Solution Processable Organic Electronics, V. G. Nazarenko, O. P. Boiko, M. I. Anisimov, A. K. Kadashchuk, Yuriy A. Nastishin, A. B. Golovin, Oleg Lavrentovich Dec 2010

Lyotropic Chromonic Liquid Crystal Semiconductors For Water-Solution Processable Organic Electronics, V. G. Nazarenko, O. P. Boiko, M. I. Anisimov, A. K. Kadashchuk, Yuriy A. Nastishin, A. B. Golovin, Oleg Lavrentovich

Chemical Physics Publications

We propose lyotropic chromonic liquid crystals (LCLCs) as a distinct class of materials for organic electronics. In water, the chromonic molecules stack on top of each other into elongated aggregates that form orientationally ordered phases. The aligned aggregated structure is preserved when the material is deposited onto a substrate and dried. The dried LCLC films show a strongly anisotropic electric conductivity of semiconductor type. The field-effect carrier mobility measured along the molecular aggregates in unoptimized films of LCLC V20 is 0.03 cm(2) V-1 s(-1). Easy processibility, low cost, and high mobility demonstrate the potential of LCLCs for ...


Second-Harmonic Generation In A Bent-Core Nematic Liquid Crystal, Seung Ho Hong, J. C. Williams, Robert J. Twieg, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt, Brett Ellman Oct 2010

Second-Harmonic Generation In A Bent-Core Nematic Liquid Crystal, Seung Ho Hong, J. C. Williams, Robert J. Twieg, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt, Brett Ellman

Chemical Physics Publications

Second-Second-harmonic generation (SHG) is studied in the magnetically aligned nematic phase of a bent-core liquid crystal (BCN) and compared to similar measurements made on a conventional rodlike (calamitic) nematic compound. The second-harmonic (SH) light detected from both materials is predominantly due to scattering and therefore incoherent. Results on the calamitic are consistent with a polarization induced by ordinary director fluctuations in the nematic phase. However, the SH scattering collected in the BCN exhibits a different temperature and angular dependence. We discuss how these differences could arise from the effects of short-range correlated, smectic-C-type molecular clusters, which have been detected in ...


Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar May 2010

Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at similar to 149 degrees C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of ...


Concentration, Temperature, And Ph Dependence Of Sunset-Yellow Aggregates In Aqueous Solutions: An X-Ray Investigation, Leela Joshi, Shin-Woong Kang, Dena Mae Agra-Kooijman, Satyendra Kumar Oct 2009

Concentration, Temperature, And Ph Dependence Of Sunset-Yellow Aggregates In Aqueous Solutions: An X-Ray Investigation, Leela Joshi, Shin-Woong Kang, Dena Mae Agra-Kooijman, Satyendra Kumar

Physics Publications

The dye sunset yellow (SY) forms columnar aggregates via π-π stacking in aqueous solutions. These aggregates develop orientational and translational order at elevated concentrations to exhibit the nematic (N) and columnar (C) mesophases. Positional-order correlation lengths of the aggregates in the directions parallel and perpendicular to the stacking direction were measured as functions of temperature, concentration, and ionic content of solutions with synchrotron x-ray scattering in magnetically aligned samples. Average length of aggregates (i.e., the number of SY molecules in an aggregate) grows monotonically with concentration while their effective transverse separation decreases. The scission energy, E, determined from ...


Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli Sep 2009

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

Chemical Physics Publications

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 ...


Membrane Organization And Ionization Behavior Of The Minor But Crucial Lipid Ceramide-1-Phosphate, Edgar Eduard Kooijman, Jesus Sot, L. Ruth Montes, Alicia Alonso, Arne Gericke, Ben De Kruijff, Satyendra Kumar, Felix M. Goni Jun 2008

Membrane Organization And Ionization Behavior Of The Minor But Crucial Lipid Ceramide-1-Phosphate, Edgar Eduard Kooijman, Jesus Sot, L. Ruth Montes, Alicia Alonso, Arne Gericke, Ben De Kruijff, Satyendra Kumar, Felix M. Goni

Biological Sciences Publications

Ceramide 1 phosphate (Cer 1 P), one of the simplest of all sphingophospholipids, occurs in minor amounts in biological membranes. Yet recent evidence suggests important roles of this lipid as a novel second messenger with crucial tasks in cell survival and inflammatory responses. We present a detailed description of the physical chemistry of this hitherto little explored membrane lipid. At full hydration Cer 1 P forms a highly organized subgel (crystalline) bilayer phase (L c) at low temperature, which transforms into a regular gel phase (L beta) at similar to 45 degrees C, with the gel to fluid phase transition ...


Membrane Organization And Ionization Behavior Of The Minor But Crucial Lipid Ceramide-1-Phosphate, Edgar E. Kooijman, Sot Jesus, L. -Ruth Montes, Alicia Alonso, Arne Gericke, Ben De Kruijff, Satyendra Kumar, Felix M. Goni Jun 2008

Membrane Organization And Ionization Behavior Of The Minor But Crucial Lipid Ceramide-1-Phosphate, Edgar E. Kooijman, Sot Jesus, L. -Ruth Montes, Alicia Alonso, Arne Gericke, Ben De Kruijff, Satyendra Kumar, Felix M. Goni

Biological Sciences Publications

Ceramide-1-phosphate (Cer-1-P), one of the simplest of all sphingophospholipids, occurs in minor amounts in biological membranes. Yet recent evidence suggests important roles of this lipid as a novel second messenger with crucial tasks in cell survival and inflammatory responses. We present a detailed description of the physical chemistry of this hitherto little explored membrane lipid. At full hydration Cer-1-P forms a highly organized subgel (crystalline) bilayer phase (L-c) at low temperature, which transforms into a regular gel phase (L-beta) at similar to 45 degrees C, with the gel to fluid phase transition (L-beta-L-alpha) occurring at similar to 65 degrees C ...


X-Ray Microscopy Study Of Chromonic Liquid Crystal Dry Film Texture, K. V. Kaznatcheev, P. Dudin, Oleg Lavrentovich, A. P. Hitchcock Dec 2007

X-Ray Microscopy Study Of Chromonic Liquid Crystal Dry Film Texture, K. V. Kaznatcheev, P. Dudin, Oleg Lavrentovich, A. P. Hitchcock

Chemical Physics Publications

Soft x-ray spectromicroscopy has been used to investigate the degree of the molecular alignment of sulfonated benzo[de]benzo[4.5]imidazo[2,1-a]isoquinoline[7,1], a lyotropic chromonic liquid crystal (LCLC). LCLC thin films cast from concentrated aqua solution (20 % wt.), aligned by shear flow and dried, show strong linear dichroism in their C-, N-, O-, S-K edge near edge x-ray spectra (NEXAFS). The carbon K edge has been used for quantitative evaluation of the orientational texture of the films at a submicron spatial scale. This has verified there is predominantly in-plane alignment of the LC director. To ...


Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, Institute Of Physics, Ukraine, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich Feb 2007

Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, Institute Of Physics, Ukraine, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich

Chemical Physics Publications

Glycerol droplets at a nematic-liquid-crystal–air interface form two different lattices—hexagonal and dense quasihexagonal—which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin.


Electric Field Dependence Of The Electric Conductivity In Liquid Crystals Made Of Bent-Core Molecules, O. G. Martins, G. Barbero, A. M. Pedreira, Antal Jakli, H. Sawade, A. M. F. Neto May 2006

Electric Field Dependence Of The Electric Conductivity In Liquid Crystals Made Of Bent-Core Molecules, O. G. Martins, G. Barbero, A. M. Pedreira, Antal Jakli, H. Sawade, A. M. F. Neto

Chemical Physics Publications

We investigate the influence of the electric field on the conductivity of an antiferroelectric liquid crystal formed by bananalike molecules. Our experimental analysis shows that large deviations of the current from a pure Ohmic behavior are observed for applied voltage of the order of the ones used for the determination of the spontaneous polarization in these types of materials. The measurements are performed in the isotropic and B-2 phases. In the isotropic phase these deviations are interpreted in terms of the model proposed by Onsager, according to which, for weak electrolyte, the conductivity depends on the actual electric field present ...


Nonlocal Model For Nematic Liquid-Crystal Elastomers, R. Ennis, L. C. Malacarne, Peter Palffy-Muhoray, M. Shelley Jan 2006

Nonlocal Model For Nematic Liquid-Crystal Elastomers, R. Ennis, L. C. Malacarne, Peter Palffy-Muhoray, M. Shelley

Chemical Physics Publications

We have developed a fully nonlocal model to describe the dynamic behavior of nematic liquid-crystal elastomers. The free energy, incorporating both elastic and nematic contributions, is a function of the material displacement vector and the orientational order parameter tensor. The free energy cost of spatial variations of these order parameters is taken into account through nonlocal interactions rather than through the use of gradient expansions. We also give an expression for the Rayleigh dissipation function. The equations of motion for displacement and orientational order are obtained from the free energy and the dissipation function by the use of a Lagrangian ...


Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Hwa Kim, Liang-Chy Chien Apr 2005

Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Hwa Kim, Liang-Chy Chien

Chemical Physics Publications

We have developed a method for stabilization of the uniform lying helix (ULH) texture of short pitch cholesterics in an electro-optical device, based on the flexoelectro-optic effect in such a texture. By using a small concentration of photoreactive liquid crystal monomer (less than 5 wt. %) and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk (localized essentially at both substrate surfaces) which stabilized efficiently the amplitude and the phase modulation modes of the device. Most importantly, the effect of the residual birefringence of the polymeric network in the field-unwound state of ...


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 Feb 2005

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

Chemical Physics Publications

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 ...


Ordered Droplet Structures At The Liquid Crystal Surface And Elastic-Capillary Colloidal Interactions, Ivan I. Smalyukh, S. Chernyshuk, B. I. Lev, A. B. Nych, U. Ognysta, V. G. Nazarenko, Oleg Lavrentovich Sep 2004

Ordered Droplet Structures At The Liquid Crystal Surface And Elastic-Capillary Colloidal Interactions, Ivan I. Smalyukh, S. Chernyshuk, B. I. Lev, A. B. Nych, U. Ognysta, V. G. Nazarenko, Oleg Lavrentovich

Chemical Physics Publications

We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.


Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni Sep 2002

Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni

Chemical Physics Publications

Monte Carlo and theoretical studies of thin 3D films of biaxial and uniaxial nematics with tangential boundary conditions show distinct differences in structure and evolution of topological defects. In the uniaxial films, defects of strength k=+/-1 are point defects that bear no bulk singularity and disappear by annihilation with each other. In the biaxial films, k=+/-1 defects are true singular bulk disclinations that split into pairs of k=+/-1/2 lines; the latter disappear by annihilation processes of the type +1/2-1/2=0. These observed differences are of relevance for the current debate on the existence of ...


Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni Dec 1997

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

Chemical Physics Publications

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.


Bilayer Smectic Order In A Mixture Of Polyphilic Liquid-Crystals, Yushan Shi, Francois G. Tournilhac, Satyendra Kumar Apr 1997

Bilayer Smectic Order In A Mixture Of Polyphilic Liquid-Crystals, Yushan Shi, Francois G. Tournilhac, Satyendra Kumar

Physics Publications

Polyphilic compounds were previously reported [F. G. Tournilhac, L. M. Blinov, J. Simon, and S. V. Yablonski, Nature 359, 621 (1992)] to form a longitudinal ferroelectric liquid crystal phase in the mixture M70 (70% compound 1, 30% compound II). The ferroelectric nature was confirmed by measurements of acoustically induced piezoelectric response and hysteretic behavior in the smectic-X' phase. We carefully examined the structure of the smectic-X' phase with high-resolution x-ray diffraction in an aligned sample and discovered bilayer structure, suggesting that molecules actually adopt antiferroelectric arrangement.


Onset And Evolution Of The Tilted Smectic Antiphase In A Polar Liquid-Crystal Binary Mixture, Yushan Shi, George Nounesis, Satyendra Kumar Aug 1996

Onset And Evolution Of The Tilted Smectic Antiphase In A Polar Liquid-Crystal Binary Mixture, Yushan Shi, George Nounesis, Satyendra Kumar

Physics Publications

High-resolution x-ray diffraction studies of a binary mixture of the n = 8 and n = 10 homologs of alkoxyphenyl nitrobenzoyloxy benzoate DBnONO2 (52.6 mole % DB10ONO2) have been performed at the onset of the tilted smectic antiphase (Sm-C) upon cooling from the smectic-A(1) phase. Fluctuations of the two competing smectic orders are found to be related to monolayer and partial bilayer ordering. With decreasing temperature, the period of the antiphase in-plane modulation increases while the smectic layer normal tilts at an angle of +/-7 degrees with respect to the director. This tilt partially recovers upon the transition to the smectic-A ...


Magnetic-Field Effect On Periodic Stripe Domains In Nematic Liquid-Crystals, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi Jan 1995

Magnetic-Field Effect On Periodic Stripe Domains In Nematic Liquid-Crystals, A. Sparavigna, Oleg Lavrentovich, A. Strigazzi

Chemical Physics Publications

Hybrid aligned nematic films placed onto an isotropic fluid substrate exhibit an unusual periodic stripe domain structure that appears only when the thickness of the film is smaller than a few tenths of a micrometer. We investigated the effect of a magnetic field on the threshold between the periodic stripe domains and the aperiodic deformed structure of the director. As experimentally observed, a magnetic field applied along the stripe domains favors a nonperiodic state with the director undistorted in the horizontal plane. The experimental findings are confirmed by a theory that takes into account not only the usual type of ...


Field-Driven 1st-Order Structural Transition In The Restricted Geometry Of A Smectic-A Cell, Oleg Lavrentovich, M. Kléman Jul 1993

Field-Driven 1st-Order Structural Transition In The Restricted Geometry Of A Smectic-A Cell, Oleg Lavrentovich, M. Kléman

Chemical Physics Publications

An external field gives rise to a first-order transition in a smectic-A cell; the transition occurs by nucleation of focal conic domains. The physical mechanisms that govern the behavior of the new domain phase are different for small (ρ≪1) and large (ρ≫1) values of the order parameters ρ [ρ=(domain radius)/(cell thickness)]. The nucleation (ρ≪1) is governed by the elastic and field energies and is facilitated by bulk or surface irregularities, while the expansion (ρ≫1) is determined by the balance of the field and anisotropic surface energy.


Confinement Effects Induced By A Solubilized Polymer On The Micellar Nematic-Lamellar Transition, Satyendra Kumar, M. R. Kuzma, W. Wedler, A. Saupe, S. Shin Jun 1992

Confinement Effects Induced By A Solubilized Polymer On The Micellar Nematic-Lamellar Transition, Satyendra Kumar, M. R. Kuzma, W. Wedler, A. Saupe, S. Shin

Physics Publications

We studied the effect of polyethylene-oxide (PEO, molecular weight from 10(5) to 4 x 10(6)) dissolved in the micellar nematic (N) and lamellar (L) phases of the surfactant system cesium perfluoro-octanoate (CsPFO)/water by microscopy and calorimetry. Replacement of water by PEO suppresses the lamellar phase above a critical concentration (w(c)) which depends on the molecular weight of the polymer by a power law. In a limited range below w(c) a reentrant nematic is observed. The N-L transitions become less sharp with increasing concentration. The observed effects are due to the disruption of the lamellar order ...