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Full-Text Articles in Physics

Cholesteric Gratings With Field-Controlled Period, Darius Subacius, Sergij V. Shiyanovskii, Philip J. Bos, Oleg Lavrentovich Dec 1997

Cholesteric Gratings With Field-Controlled Period, Darius Subacius, Sergij V. Shiyanovskii, Philip J. Bos, Oleg Lavrentovich

Chemical Physics Publications

Diffractive gratings with period varied by an electric field are developed using a cholesteric liquid crystal confined between two transparent electrodes with unidirectionally treated alignment layers. In the initial state (zero field), the cholesteric layers are parallel to the cell planes. The electric field creates an in-plane modulated structure of variable period. Diffraction regimes of both Raman-Nath and Bragg types are demonstrated. (C) 1997 American Institute of Physics.


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.


Efficient, Polarization-Independent, Reflective Liquid Crystal Phase Grating, C. M. Titus, Philip J. Bos Oct 1997

Efficient, Polarization-Independent, Reflective Liquid Crystal Phase Grating, C. M. Titus, Philip J. Bos

Chemical Physics Publications

A reflective liquid crystal diffraction grating is proposed which makes use of the maximum available surface area. The structure consists of alternating stripes, each a twisted-nematic domain with surface orientation perpendicular to that of its neighbors. All domains have the same twist sense. This device yields, in principle, 100% diffraction efficiency independent of incident polarization. (C) 1997 American Institute of Physics.


Switchable Diffractive Cholesteric Gratings, Darius Subacius, Philip J. Bos, Oleg Lavrentovich Sep 1997

Switchable Diffractive Cholesteric Gratings, Darius Subacius, Philip J. Bos, Oleg Lavrentovich

Chemical Physics Publications

Electrically switchable diffractive gratings based on cholesteric liquid crystals are suggested. An electric field switches the cholesteric cell between three states: two with a uniform in-plane director and one with a periodic in-plane director modulation. The modulated state produces a Raman-Nath diffractive effect. Characteristic time of switching is of the order of 10 ms. Diffractive properties depend on the polarization of the incident beam and the direction of surface orientation. (C) 1997 American Institute of Physics.


Electro-Optical Study Of Nematic Elastomer Gels, C.C. Chang, Liang-Chy Chien, R. B. Meyer Jul 1997

Electro-Optical Study Of Nematic Elastomer Gels, C.C. Chang, Liang-Chy Chien, R. B. Meyer

Chemical Physics Publications

We report on an electro-optical study of a liquid-crystal-polymer composite system. This system is made by dissolving a small amount of acrylate monomers (8%) plus crosslinkers in a nematic liquid crystal, and then photopolymerizing the homogeneous mixture. These nematic gels show properties different from those of ordinary nematics or polymer stabilized liquid crystals. By studying the electric field induced Frederiks transition, some basic propel-ties of the nematic gels can be deduced. We compare the experimental results to a simple phenomenological model of the nematic gel, involving a characteristic length scale of order 1 mu m, which is also visible as ...


Dual Frequency Cholesteric Light Shutters, Ming Xu, Deng-Ke Yang Feb 1997

Dual Frequency Cholesteric Light Shutters, Ming Xu, Deng-Ke Yang

Chemical Physics Publications

We developed a dual frequency cholesteric light shutter which utilizes a cholesteric liquid crystal; the dielectricanisotropy of the material changes from positive to negative when the frequency of applied voltage is increased. The shutters are switched to the transparent homeotropic texture by low frequency voltages, and switched to the reflecting planar texture by high frequency voltages. We designed a waveform which reduced the transition time from the homeotropic texture to the planar texture to less than 100 ms.


Pretransitional Nematic Ordering In Liquid Crystals With Dispersed Polymer Networks, Y. K. Fung, A. Borstnik, S. Zumer, Deng-Ke Yang, J. William Doane Feb 1997

Pretransitional Nematic Ordering In Liquid Crystals With Dispersed Polymer Networks, Y. K. Fung, A. Borstnik, S. Zumer, Deng-Ke Yang, J. William Doane

Chemical Physics Publications

The birefringence induced by partially ordered polymer networks dispersed in an isotropic phase of liquid crystals is studied. Polymer networks were formed by the polymerization of 1-4 % mixtures of prepolymer in the nematic phase of liquid crystals. The partial nematic (paranematic) ordering is analyzed in terms of the Landau-de Gennes approach using a simple model of an array of thin fibrils, which can, on a large scale, form bundles of polymer-rich material. The comparison of the theory and birefringence data clearly shows that the main building bloc of the network is a few nanometers thick fibril. The average thickness of ...


Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. B. Meyer Jan 1997

Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. B. Meyer

Chemical Physics Publications

We report a piezolectric effect in cholesteric liquid crystalline elastomer gels. When we apply a shear stress to a cholesteric elastomer gel in the direction perpendicular to its helical axis, a polarization can be induced in the direction perpendicular to both the stress and the helix. This experimental observation agrees with the theory proposed by Pelcovits and Meyer [J. Phys. II France 5, 877 (1995)].