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Full-Text Articles in Physics

Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. V. Yaroshchuk, L G. Cada, M. Sonpatki, Liang-Chy Chien Jul 2001

Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. V. Yaroshchuk, L G. Cada, M. Sonpatki, Liang-Chy Chien

Chemical Physics Publications

A liquid-crystal (LC) photoalignment method, based on the use of low-molecular-weight photo-cross-linkable (LMWPC) composites is proposed. The basic idea of this method is that cross linking or both cross linking and polymerization of LMWPC composites are realized immediately on the substrate simultaneously with the photoalignment or as a stage of the backing process. Providing the advantages of a conventional photoalignment method, the use of LMWPC composites simplifies the synthesis and alignment procedure, makes possible wide range control of pretilt angles, and enhances the thermal stability of the LC alignment. The abilities of this method are demonstrated using a series of ...


Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke Jun 2001

Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke

Chemical Physics Publications

The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-C-G phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C-1 symmetry). The observations suggest that the phase tentatively labeled as B-7 is identical with the Sm-C-G phase.


Switchable Diffraction Gratings Based On Inversion Of The Dielectric Anisotropy In Nematic Liquid Crystals, S. W. Kang, Samuel N. Sprunt, Liang-Chy Chien Jun 2001

Switchable Diffraction Gratings Based On Inversion Of The Dielectric Anisotropy In Nematic Liquid Crystals, S. W. Kang, Samuel N. Sprunt, Liang-Chy Chien

Chemical Physics Publications

A switchable liquid crystal diffraction grating, responsive to both the frequency and magnitude of an applied voltage, is demonstrated. The grating is based on polymer stabilization of modulated states of the liquid crystal optic axis induced at frequencies near a sign inversion of the dielectric anisotropy. In a particular case of frequency-based switching, 70% of the transmitted intensity of a 633 nm laser beam can be shifted into or out of a +/-12 degrees forward are by changing the frequency of an applied voltage between 10 and 16 kHz at a fixed amplitude of 27 V. (C) 2001 American Institute ...


Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien Jun 2001

Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien

Chemical Physics Publications

The transfer of chirality from nonchiral polymer networks to the racemic B2 phase of nonchiral banana-shaped molecules is demonstrated. This corresponds to the transfer of chirality from an achiral material to another achiral material. There are two levels of chirality transfers. (a) On a microscopic level the presence of a polymer network (chiral or nonchiral) favors a chiral state over a thermodynamically stable racemic state due to the inversion symmetry breaking at the polymer-liquid crystal interfaces. (b) A macroscopically chiral (enantimerically enriched) sample can be produced if the polymer network has a helical structure, and/or contains chemically chiral groups ...


Optical Studies Of The Liquid Crystal B2 Phase Formed By Banana-Shaped Molecules, D. A. Olson, M. Veum, A. Cady, M. V. D'Agostino, P. M. Johnson, H. T. Nguyen, Liang-Chy Chien, C. C. Huang Apr 2001

Optical Studies Of The Liquid Crystal B2 Phase Formed By Banana-Shaped Molecules, D. A. Olson, M. Veum, A. Cady, M. V. D'Agostino, P. M. Johnson, H. T. Nguyen, Liang-Chy Chien, C. C. Huang

Chemical Physics Publications

Null-transmission ellipsometry and depolarized light microscopy have been performed on free-standing films of three achiral banana-shaped compounds in the B2 phase. Our results support a two-layer unit cell previously proposed to explain the observed antiferroelectricity in thin films and bulk samples. We have studied thicker films than previously reported and have found no deviations in the film structure from the earlier findings. Moreover, we can determine the layer spacing, the molecular tilt from the layer normal, and the three principal indices of refraction in the molecular reference frame.


Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. N. Lee, J. Kelly, Liang-Chy Chien Mar 2001

Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. N. Lee, J. Kelly, Liang-Chy Chien

Chemical Physics Publications

We applied ellipsometry to study the distribution of azobenzene fragments in the films of two types of comblike polymers with azobenzene moieties in the side chains before and after ultraviolet ~UV! light irradiation. The polymer with an alkyl chain at the end of the azobenzene fragment forms structures with preferred homeotropic alignment of the fragments. Irradiation of this polymer with nonpolarized UV light at normal incidence induces a homeotropic alignment of azobenzene fragments. Oblique irradiation induces tilted structures. Polarized UV light irradiation at normal beam incidence induces biaxial structures with a fanlike distribution of azobenzene fragments and preferably out-of-plane alignment ...


Undulations In A Confined Lamellar System With Surface Anchoring, T. Ishikawa, Oleg Lavrentovich Feb 2001

Undulations In A Confined Lamellar System With Surface Anchoring, T. Ishikawa, Oleg Lavrentovich

Chemical Physics Publications

We visualize undulations in layered systems using a cholesteric stripe phase with a macroscopic supramicron periodicity. The wave vector of stripe pattern is in the cell's plane. The-undulation is induced by an in-plane magnetic field normal to the stripes. The observed displacement of layers is much larger than the value predicted by the Helfrich-Hurault classic theory. We propose a model of undulations that explains the data by finite surface anchoring of layers.


Design Optimized Bistable Twisted Nematic Liquid Crystal Display, Bin Wang, Philip J. Bos Jan 2001

Design Optimized Bistable Twisted Nematic Liquid Crystal Display, Bin Wang, Philip J. Bos

Chemical Physics Publications

The difference between the equilibrium and switching d/p ratio of a bistable twisted nematic (BTN) liquid crystal display is shown by computer simulation. It is clearly indicated that the optimized d/p ratio has to be determined by the switching rather than equilibrium d/p ratio. It is also shown that the switching d/p ratio is related not only to the pre-tilt angle, but also to liquid crystal viscosities, which indirectly indicates how temperature will affect the BTN device, and that there exists an optimized delay time for the device-driving waveform which will narrow the selection pulse and ...


How To Achieve Zigzag Free Sm-C * State With A Low Pretilt Angle: A Numerical Calculation, Chenhui Wang, Ryuji Kurihara, Philip J. Bos, Shunsuke Kobayashi Jan 2001

How To Achieve Zigzag Free Sm-C * State With A Low Pretilt Angle: A Numerical Calculation, Chenhui Wang, Ryuji Kurihara, Philip J. Bos, Shunsuke Kobayashi

Chemical Physics Publications

One of the most notorious problems with ferroelectric liquid crystal is obtaining zigzag free bistable devices. By investigating the balance between surface azimuthal anchoring energy and bulk elastic energy within the confined chevron layer geometry of C1 and C2, we propose that it is possible to get a zigzag free C1 state by low azimuthal anchoring alignment at a low pretilt angle. The critical azimuthal anchoring coefficient for the defect free C1 state is calculated. Its relationships with elastic constant, chevron angle, as well as surface topography effect are also discussed. (C) 2001 American Institute of Physics.


Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray Jan 2001

Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray

Chemical Physics Publications

We study theoretically the Saffman-Taylor instability of an air bubble expanding into a non-Newtonian fluid in a Hele-Shaw cell, with the motivation of understanding suppression of tip-splitting and the formation of dendritic structures observed in the flow of complex fluids, such as polymeric liquids or liquid crystals. A standard visco-elastic flow model is simplified in the case of flow in a thin gap, and it is found that there is a distinguished limit where shear thinning and normal stress differences are apparent, but elastic response is negligible. This observation allows formulation of a generalized Darcy's law, where the pressure ...