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Chemical Physics Publications

Transition

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Full-Text Articles in Physics

Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung Jan 2013

Simulation Study Of Seemingly Fickian But Heterogeneous Dynamics Of Two Dimensional Colloids, Jeongmin Kim, Chanjoong Kim, Bong June Sung

Chemical Physics Publications

A two-dimensional (2D) solid lacks long-range positional order and is diffusive by means of the cooperative motion of particles. We find from molecular dynamics simulations of hard discs that 2D colloids in solid and hexatic phases show seemingly Fickian but strongly heterogeneous dynamics. Beyond translational relaxation time, the mean-square displacement is linear with time, t, implying that discs would undergo Brownian diffusion and the self-part of the van Hove correlation function [G(s)(r, t)] might be Gaussian. But dynamics is still heterogeneous and G(s)(r, t) is exponential at large r and oscillatory with multiple peaks at intermediate ...


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 ...


Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar Jun 2012

Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar

Chemical Physics Publications

Deuteron nuclear magnetic resonance is used to study the phase segregation behavior of photoisomerizable liquid crystal diheptylazobenzene (7AB) confined into cylindrical pores of Anopore membranes. It is demonstrated that the concentration of both components in a binary trans-7AB and cis-7AB mixture can be controlled dynamically using UV-illumination stimulated trans-to-cisphotoisomerization and thermally induced cis-to-trans backisomerization. The so far elusive temperature-concentration phase diagram of such system is determined by comparative analysis of the behavior in bulk, thin-planar, and Anopore-confining geometry.


Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione Jun 2008

Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione

Chemical Physics Publications

An experimental study of the heat capacity, mass density, magnetic-field-induced optical birefringence, linewidth and intensity of scattered light, and the viscosities associated with nematic order parameter fluctuations and fluid flow has been performed on an achiral bent-core liquid crystal above its clearing point temperature. The measurements reveal a transition between two optically isotropic phases that is consistent with recent theoretical predictions of a "tetrahedratic" form of orientational order.


Smectic-A-Filled Birefringent Elements And Fast Switching Twisted Dual-Frequency Nematic Cells Used For Digital Light Deflection, Oleg Pishnyak, Andrii Golovin, Liubov Kreminska, John J. Pouch, Felix A. Miranda, Bruce K. Winker, Oleg Lavrentovich Apr 2006

Smectic-A-Filled Birefringent Elements And Fast Switching Twisted Dual-Frequency Nematic Cells Used For Digital Light Deflection, Oleg Pishnyak, Andrii Golovin, Liubov Kreminska, John J. Pouch, Felix A. Miranda, Bruce K. Winker, Oleg Lavrentovich

Chemical Physics Publications

We describe the application of smectic A (SmA) liquid crystals for beam deflection. SmA materials can be used in digital beam deflectors (DBDs) as fillers for passive birefringent prisms. SmA prisms have high birefringence and can be constructed in a variety of shapes, including single prisms and prismatic blazed gratings of different angles and profiles. We address the challenges of uniform alignment of SmA, such as elimination of focal conic domains. Fast rotation of the incident light polarization in DBDs is achieved by an electrically switched 90-deg twisted nematic (TN) cell.


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 Aug 2005

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

Chemical Physics Publications

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 ...


Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli Dec 2002

Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli

Chemical Physics Publications

The dielectric fluctuations in the uniaxial nematic phase of a bent-core liquid crystal have been studied by dynamic light scattering. Polarization selection of the scattering cross-section reveals one mode due to ordinary director fluctuations and, in the lower part of the nematic phase, a second mode attributable to fluctuations of the biaxial order parameter. The director fluctuations are similar to100 times slower than observed in typical nematics based on straight-core molecules, suggesting that the bent core nematogenic units may be microscopic smectic domains ("cybotactic" clusters).


Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich Oct 1999

Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich

Chemical Physics Publications

We analyze the high-electric-field technique designed by Yokoyama and van Sprang [J. Appl. Phys. 57, 4520 (1985)] to determine the polar anchoring coefficient W of a nematic liquid crystal-solid substrate. The technique implies simultaneous measurement of the optical phase retardation and capacitance as functions of the applied voltage well above the threshold of the Frederiks transition. We develop a generalized model that allows for the determination of W for tilted director orientation. Furthermore, the model results in a new high-field technique, (referred to as the RV technique), based on the measurement of retardation versus applied voltage. W is determined from ...


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.


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 ...


Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik Aug 1994

Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik

Chemical Physics Publications

To verify the status of the divergence K13 term in the elastic theory of liquid crystals we study submicron films placed onto an isotropic fluid substrate in the Langmuir trough (Langmuir liquid crystal, LLC). The upper and lower surfaces favor normal and tangential molecular orientation, respectively. The periodic domain phase is observed in a nematic LLC. The dependence of the periodicity L of the domains vs film thickness h can be explained only if the elastic energy is accompanied by divergence terms with nonzero constants K13 and K24. It is found that for 5CB K13 almost-equal-to -0.2K11.


Ordering And Self-Diffusion In The 1st Molecular Layer At A Liquid-Crystal Polymer Interface, G. P. Crawford, Deng-Ke Yang, S. Zumer, D. Finotello, J. William Doane Aug 1990

Ordering And Self-Diffusion In The 1st Molecular Layer At A Liquid-Crystal Polymer Interface, G. P. Crawford, Deng-Ke Yang, S. Zumer, D. Finotello, J. William Doane

Chemical Physics Publications

H-2 NMR of a liquid crystal confined to submicron cylindrical cavities, in a 17-K interval above the nematic-isotropic transition, reveals a weakly orientationally ordered molecular layer at the cavity wall governed by local interactions. The order (S0 = 0.02) is temperature independent so that a partial wetting is realized with no prewetting transition expected. A molecular exchange rate between the surface layer and the bulk is measured to be approximately 10(3) s-1. The coherence length measuring the order penetrating further into the cavity is described by alpha = 0.4 and xi-0 = 0.6 nm.