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Chemical Physics Publications

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Full-Text Articles in Physics

Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger May 2013

Statistical Mechanics Of Bend Flexoelectricity And The Twist-Bend Phase In Bent-Core Liquid Crystals, Shaikh M. Shamid, Subas Dhakal, Jonathan V. Selinger

Chemical Physics Publications

We develop a Landau theory for bend flexoelectricity in liquid crystals of bent-core molecules. In the nematic phase of the model, the bend flexoelectric coefficient increases as we reduce the temperature toward the nematic to polar phase transition. At this critical point, there is a second-order transition from high-temperature uniform nematic phase to low-temperature nonuniform polar phase composed of twist-bend or splay-bend deformations. To test the predictions of Landau theory, we perform Monte Carlo simulations to find the director and polarization configurations as functions of temperature, applied electric field, and interaction parameters.


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 ...


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 ...


Surface Alignment, Anchoring Transitions, Optical Properties, And Topological Defects In The Nematic Phase Of Thermotropic Bent-Core Liquid Crystal A131, B. Senyuk, H. Wonderly, M. Mathews, Q. Li, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2010

Surface Alignment, Anchoring Transitions, Optical Properties, And Topological Defects In The Nematic Phase Of Thermotropic Bent-Core Liquid Crystal A131, B. Senyuk, H. Wonderly, M. Mathews, Q. Li, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study optical, structural, and surface anchoring properties of thermotropic nematic bent-core material A131. The focus is on the features associated with orientational order as the material has been reported to exhibit not only the usual uniaxial nematic but also the biaxial nematic phase. We demonstrate that A131 experiences a surface anchoring transition from a perpendicular to tilted alignment when the temperature decreases. The features of the tilted state are consistent with surface-induced birefringence associated with smectic layering near the surface and a molecular tilt that changes along the normal to the substrates. The surface-induced birefringence is reduced to zero ...


Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray Jun 2007

Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray

Chemical Physics Publications

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic expression ...


Distance Of Closest Approach Of Two Arbitrary Hard Ellipsoids, Xiaoyu Zheng, Wilder Iglesias, Peter Palffy-Muhoray Jun 2007

Distance Of Closest Approach Of Two Arbitrary Hard Ellipsoids, Xiaoyu Zheng, Wilder Iglesias, Peter Palffy-Muhoray

Chemical Physics Publications

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic expression ...


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 ...


Deuteron Nmr Investigation Of A Photomechanical Effect In A Smectic-A Liquid Crystal, Boštjan Zalar, Oleg Lavrentovich, Huairen Zeng, Daniele Finotello Aug 2000

Deuteron Nmr Investigation Of A Photomechanical Effect In A Smectic-A Liquid Crystal, Boštjan Zalar, Oleg Lavrentovich, Huairen Zeng, Daniele Finotello

Chemical Physics Publications

Deuteron quadrupole-perturbed NMR is used to study the perturbation of orientational order in a smectic-A liquid crystal (octylcyanobiphenyl or 8CB) caused by photoinduced trans-to-cis isomerization of a photosensitive dopant (diheptylazobenzene or 7AB). The time and temperature dependences of the orientational order were independently studied for 8CB, 7AB, and their mixtures. Upon UV irradiation that causes trans-to-cis isomerization of 7AB, the orientational order parameter of the smectic-A phase is reduced. Relaxation in the dark exponentially restores the equilibrium value of the order parameter. The characteristic time for this process closely matches the lifetimes of the 7AB excited state. While ...