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Full-Text Articles in Physics
Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. Lee, J. Kelly, Liang-Chy Chien
Light Induced Structures In Liquid Crystalline Side-Chain Polymers With Azobenzene Functional Groups, O. Yaroschuk, Tatiana Sergan, J. Lindau, S. Lee, J. Kelly, Liang-Chy Chien
Liang-Chy Chien
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. …
Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Kim, Liang-Chy Chien
Short Pitch Cholesteric Electro-Optical Device Stabilized By Nonuniform Polymer Network, Sang Kim, Liang-Chy Chien
Liang-Chy Chien
We have developed a method for stabilization of the uniform lying helix (ULH) texture of short pitch cholesterics in an electro-optical device, based on the flexoelectro-optic effect in such a texture. By using a small concentration of photoreactive liquid crystal monomer (less than 5 wt. %) and selecting the illumination conditions, we were able to create a nonuniform polymeric network in the liquid crystal bulk (localized essentially at both substrate surfaces) which stabilized efficiently the amplitude and the phase modulation modes of the device. Most importantly, the effect of the residual birefringence of the polymeric network in the field-unwound state …
Structure And Morphology Of Polymer-Stabilized Cholesteric Diffraction Gratings, Shin-Woong Kang, Samuel Sprunt, Liang-Chy Chien
Structure And Morphology Of Polymer-Stabilized Cholesteric Diffraction Gratings, Shin-Woong Kang, Samuel Sprunt, Liang-Chy Chien
Liang-Chy Chien
We report a study of polymer network morphology in planar diffraction gratings formed from polymer-stabilized cholesteric liquid crystals. Photopolymerizing a mesogenic monomer yields a regular sawtooth morphology, composed of polymer sheets running at an acute angle between thick, uniformly aligned bundles which reside on the opposing substrates. To explain this morphology and evidence of two grating vectors in the diffraction pattern, we propose a model for the liquid-crystal director where out-of-phase twists at the surfaces gear into an interior twist, which has half the period of the surface twist, via splay distortions running between the substrates. The morphology also changes …
Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John West, Liang-Chy Chien, J. Doane
Control Of Reflectivity And Bistability In Displays Using Cholesteric Liquid-Crystals, Deng-Ke Yang, John West, Liang-Chy Chien, J. Doane
Liang-Chy Chien
It is demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Dispersing a polymer in the liquid crystal or using a cell with an inhomogeneous surface anchoring creates permanent defects which result in long-term bistability, high contrast at large viewing angles, and gray scale. The wide-angle, reflective feature makes cholesteric materials suitable for displays without backlights and bistability provides flicker-free operation.
Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien
Field-Induced And Polymer-Stabilized Two-Dimensional Cholesteric Liquid Crystal Gratings, Shin-Woong Kang, Liang-Chy Chien
Liang-Chy Chien
The authors experimentally demonstrate an electrically switchable gratings based on polymer-stabilized, field-induced two-dimensional square-lattice pattern of a cholesteric liquid crystal. A dependence of the two-dimensional diffraction patterns with the magnitude of applied voltage is observed for before and after the polymer stabilization. The diffraction efficiency reaches 84% calculated for the zero order light intensity at the applied voltage of 0.23 V/mu m for a 10 mu m thick sample.
Dynamical Studies Of Gratings Formed In Polymer-Dispersed Liquid Crystal Films, Andy Fuh, T. Ko, M. Tsai, C. Huang, Liang-Chy Chien
Dynamical Studies Of Gratings Formed In Polymer-Dispersed Liquid Crystal Films, Andy Fuh, T. Ko, M. Tsai, C. Huang, Liang-Chy Chien
Liang-Chy Chien
The use of polymer-dispersed liquid crystal films to fabricate gratings was demonstrated. The written gratings are permanent, but are electrically switchable. In this article, we report the results obtained from the dynamical studies of gratings formed in polymer-dispersed liquid crystal films having various liquid crystal-polymer mixing ratios. The results showed that during the initial phases of formation, a thermal grating effect dominated. Later, it was offset or quenched by the photopolymerization effect which eventually dominated and determined the characteristics of the final grating.
Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. Yaroshchuk, K. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau
Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. Yaroshchuk, K. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau
Liang-Chy Chien
We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced three-dimensional (3D) orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, respectively. Using irradiation with the polarized light of two different wavelengths, we find that the kinetics of photoinduced anisotropy can be dominated by …
Nematic Director Orientation In A Liquid-Crystal-Dispersed Polymer - A Deuterium Nmr Approach, Ralf Stannarius, G. Crawford, Liang-Chy Chien, J. Doane
Nematic Director Orientation In A Liquid-Crystal-Dispersed Polymer - A Deuterium Nmr Approach, Ralf Stannarius, G. Crawford, Liang-Chy Chien, J. Doane
Liang-Chy Chien
The nuclear-magnetic-resonance (NMR) technique is employed to liquid-crystal-dispersed-polymer (LCDP) systems. Deuterium NMR is used to determine director distributions in LCDP cells in the presence of a magnetic field. The samples consist of a nematic liquid crystal mixed with small percentages of a monomer that is polymerized under different conditions after dissolving it in the liquid crystal. NMR spectra of the deuterated liquid-crystal molecules give information on orientation and order in such systems. The orientation of the polymer skeleton formed during the polymerization is found to be stable. It determines the orientation of the nematic director even in the presence of …
Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. Meyer
Piezoelectric Effects In Cholesteric Elastomer Gels, C. C. Chang, Liang-Chy Chien, R. Meyer
Liang-Chy Chien
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)].
Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar
Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar
Liang-Chy Chien
Internal polymer columnar structures in liquid crystal (LC) cells have been produced using the method of thermally-induced phase separation of LC/prepolymer solution and solidified by photopolymerization. These polymer columns adhere to both substrates and enhance control of the LC cell spacing and mechanical stability. The existence and profile of the polymer columns were investigated by optical and scanning electron microscopy techniques. Supertwisted nematic LC cells with polymer columnar structures have been constructed using this method and their electro-optical characteristics measured.
Double Twist In Helical Polymer "Soft" Crystals, Christopher Li, Stephen Cheng, Jason Ge, Feng Bai, John Zhang, Ian Mann, Frank Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
Double Twist In Helical Polymer "Soft" Crystals, Christopher Li, Stephen Cheng, Jason Ge, Feng Bai, John Zhang, Ian Mann, Frank Harris, Liang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz
Liang-Chy Chien
In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first …
Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. Yaroshchuk, L Cada, M. Sonpatki, Liang-Chy Chien
Liquid-Crystal Photoalignment Using Low-Molecular-Weight Photo-Cross-Linkable Composites, O. Yaroshchuk, L Cada, M. Sonpatki, Liang-Chy Chien
Liang-Chy Chien
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 …
Cholesteric Liquid-Crystal Polymer Dispersion For Haze-Free Light Shutters, Deng-Ke Yang, Liang-Chy Chien, J. Donae
Cholesteric Liquid-Crystal Polymer Dispersion For Haze-Free Light Shutters, Deng-Ke Yang, Liang-Chy Chien, J. Donae
Liang-Chy Chien
A new dispersion involving a polymer in low concentration with a cholesteric liquid crystal is reported. Two types of light modulators from these materials are described as a normal mode shutter which is opaque (light scattering) in the field-OFF state and transparent in the field-ON state and a reverse-mode shutter with the opposite field conditions. The transparent state of both cells is haze-free for all viewing angles making the material attractive for window applications and direct view displays.
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. Kim, Liang-Chy Chien, A. Saupe
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. Kim, Liang-Chy Chien, A. Saupe
Liang-Chy Chien
Polymer dispersions were made by photoinduced polymerization of 4,4'-bisacryloyl-biphenyl in liquid crystal 4-4'-cyano pentyl biphenyl as nematic solvent. Samples were prepared with 0.5, 1, and 1.5 wt % monomer. The polymerization was done in the isotropic phase. The rotational viscosities of the two lower concentration samples increased only moderately after UV curing (3 mW/cm2, 25 min). The 1.5 wt % sample gave under the same condition a nematic with a fairly rigid anisotropic network that did not realign in magnetic field up to 20 kG. We estimate that the mesh size of the network was in the order of 1 …