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Full-Text Articles in Physics

One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray Mar 2011

One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray

Chemical Physics Publications

In this paper, we present a simple one tensor mean field model of biaxial nematic liquid crystals. The salient feature of our approach is that material parameters appear explicitly in the order parameter tensor. We construct the free energy from a mean field potential based on anisotropic dispersion interactions, identify the order parameter tensor and its elements, and obtain self-consistent equations, which are then solved numerically. The results are illustrated in a 3D ternary phase diagram. The phase behavior can be simply related to molecular parameters. The results may be useful for designing molecules that show a thermotropic biaxial phase.


Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal, Min Sang Park, Beom-Kin Yoon, Jung Ok Park, Veena Prasad, Satyendra Kumar, Mohan Srinivasarao Jul 2010

Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal, Min Sang Park, Beom-Kin Yoon, Jung Ok Park, Veena Prasad, Satyendra Kumar, Mohan Srinivasarao

Physics Publications

Polarized Raman spectroscopy was used to investigate the development of orientational order and the degree of phase biaxiality in a bent-core mesogenic system. The values of the uniaxial order parameters ⟨P200⟩ and ⟨P400⟩, and biaxial order parameters ⟨P220⟩, ⟨P420⟩, and ⟨P440⟩, and their evolution with temperature were determined. The temperature dependence of almost all order parameters reveals a second order transition from the uniaxial to biaxial nematic phase with ⟨P220⟩ increasing to ∼0.22 before a first order transition to the smectic-C phase, upon cooling.


Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan Selinger May 2009

Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan Selinger

Chemical Physics Publications

Recent experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals-increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. To understand these effects, we develop a theory for the statistical mechanics of ferroelectric nanoparticles in liquid crystals. This theory predicts the enhancements of liquid-crystal properties, in good agreement with experiments. These predictions apply even when electrostatic interactions are partially screened by moderate concentrations of ions.


Landau-De Gennes Theory Of Biaxial Nematics Reexamined, David W. Allender, Lech Longa Jul 2008

Landau-De Gennes Theory Of Biaxial Nematics Reexamined, David W. Allender, Lech Longa

Physics Publications

Recent experiments report that the long-looked-for thermotropic biaxial nematic phase has been finally detected in some thermotropic liquid crystalline systems. Inspired by these experimental observations, we concentrate on some elementary theoretical issues concerned with the classical sixth-order Landau-de Gennes free energy expansion in terms of the symmetric and traceless tensor order parameter Q(alpha beta). In particular, we fully explore the stability of the biaxial nematic phase giving analytical solutions for all distinct classes of the phase diagrams that theory allows. This includes diagrams with triple, critical, and tricritical points and with multiple (reentrant) biaxial and uniaxial phase transitions. A ...


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.


Orientational Coupling Amplification In Ferroelectric Nematic Colloids, Fenghua Li, Oleksandr Buchnev, Chae Il Cheon, Anatoliy Glushchenko, Victor Reshetnyak, Yuri Reznikov, Timothy J. Sluckin, John L. West Oct 2006

Orientational Coupling Amplification In Ferroelectric Nematic Colloids, Fenghua Li, Oleksandr Buchnev, Chae Il Cheon, Anatoliy Glushchenko, Victor Reshetnyak, Yuri Reznikov, Timothy J. Sluckin, John L. West

Chemistry & Biochemistry Publications

We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy, and capacitance studies. The resulting homogeneous colloids possess a significantly amplified nematic orientational coupling. We find that the nematic orientation coupling increases by similar to 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases by up to 40 degrees C compared to the pure liquid crystal host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square ...


Elasticity-Mediated Self-Organization And Colloidal Interactions Of Solid Spheres With Tangential Anchoring In A Nematic Liquid Crystal, Ivan I. Smalyukh, Oleg Lavrentovich, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad Oct 2005

Elasticity-Mediated Self-Organization And Colloidal Interactions Of Solid Spheres With Tangential Anchoring In A Nematic Liquid Crystal, Ivan I. Smalyukh, Oleg Lavrentovich, A. N. Kuzmin, A. V. Kachynski, P. N. Prasad

Chemical Physics Publications

Using laser tweezers, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with tangential surface anchoring. The interactions overcome the Brownian motion when the interparticle separation r ->(p) is less than 3 particle diameters. The particles attract when the angle theta between r ->(p) and the uniform far-field director n(0) is between 0 degrees and approximate to 70 degrees and repel when 75 degrees less than or similar to theta(0) and, at higher concentrations, form complex kinetically trapped structures.