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Full-Text Articles in Physics

Fast Switching Dual-Frequency Liquid Crystal Optical Retarder, Driven By An Amplitude And Frequency Modulated Voltage, Andrii B. Golovin, Sergij V. Shiyanovskii, Oleg Lavrentovich Nov 2003

Fast Switching Dual-Frequency Liquid Crystal Optical Retarder, Driven By An Amplitude And Frequency Modulated Voltage, Andrii B. Golovin, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We demonstrate theoretically and experimentally a fast-switching nematic optical retarder capable to switch a few microns of optical retardation in less than 1 ms. For example, a nematic cell of thickness 14.5 mum switches 0.3 mum of retardation within 0.15 ms and 2.5 mum within 0.5 ms for single passage of beam. The corresponding figure of merit is two orders of magnitude higher than the one known for the best nematic materials synthesized so far. The fit is achieved by employing a dual-frequency nematic liquid crystal in high-pretilt angle cells and a special addressing scheme ...


Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar Nov 2003

Formation And Localization Of Internal Polymer Columnar Structures In Liquid Crystal Cells, Qingbing Wang, Liang-Chy Chien, Satyendra Kumar

Chemical Physics Publications

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.


Optical Studies Of The Nematic Phase Of An Oxazole-Derived Bent-Core Liquid Crystal, J. A. Olivares, S. Stojadinovic, T. Dingemans, Samuel N. Sprunt, Antal Jákli Oct 2003

Optical Studies Of The Nematic Phase Of An Oxazole-Derived Bent-Core Liquid Crystal, J. A. Olivares, S. Stojadinovic, T. Dingemans, Samuel N. Sprunt, Antal Jákli

Chemical Physics Publications

Various optical and dynamic light scattering studies have been conducted on the nematic phase of an oxazole-derived bent-core liquid crystal. At optical length scales and in the absence of applied fields, homogeneously aligned samples of this material, which has an oxazole heterocyclic ring in the central core, are found to behave more like a conventional straight-core nematic than a previously investigated ester-based class of bent-core molecules that have a benzene ring as the core linkage between the two arms of the bow-shaped molecule. In particular, the nematic refractive indices of the oxazole compound combine in the standard way [i.e ...


Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. V. Yaroshchuk, K. D. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau Jul 2003

Photoinduced Three-Dimensional Orientational Order In Side Chain Liquid Crystalline Azopolymers, O. V. Yaroshchuk, K. D. Kiselev, Yu. Zakrevskyy, T. Bidna, J. Kelly, Liang-Chy Chien, J. Lindau

Chemical Physics Publications

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 ...


Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair May 2003

Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair

Chemical Physics Publications

Although the liquid-crystal research is well established in science, there are newly emerging exciting systems, that deserve extensive basic studies. One of these areas is the research of the bent-shaped molecules (so-called "banana liquid crystals"), which have delicate chirality and polarity properties. In this paper we show that these materials also have very unusual rheological features, such as the formation of stable fluid fibers and bridges. Under electric fields, these objects present striking mechanical effects, such as horizontal and transversal vibrations. Studies indicate that the research of banana-liquid-crystal fibers may lead to new type of artificial muscle systems.


Fast Q-Tensor Method For Modeling The Dynamics Of Defects In A Liquid Crystal Director Field, Philip J. Bos, Gi-Dong Lee, Seon Hong Ahn, Kyeong Hyeon Kim Apr 2003

Fast Q-Tensor Method For Modeling The Dynamics Of Defects In A Liquid Crystal Director Field, Philip J. Bos, Gi-Dong Lee, Seon Hong Ahn, Kyeong Hyeon Kim

Chemical Physics Publications

A fast Q-tensor method, which can model the defect dynamics in a liquid crystal director field, is presented. Conceptually based on the Oseen-Frank approach, we have added temperature energy density terms in addition to the strain energy terms, and an improved normalization method for fast calculations. The method is more compact and allows a larger time step than previous methods. The method is used to model the defect dynamics occurring during the topological state change from a splay to bend director field configuration.


Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli Apr 2003

Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli

Chemical Physics Publications

The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C*(SmC*) to AF1 phase transition (around 103.0 °C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmCA*) and AF2 (SmCA*) phases very ...


Anchoring-Mediated Interaction Of Edge Dislocations With Bounding Surfaces In Confined Cholesteric Liquid Crystals, Ivan I. Smalyukh, Oleg Lavrentovich Feb 2003

Anchoring-Mediated Interaction Of Edge Dislocations With Bounding Surfaces In Confined Cholesteric Liquid Crystals, Ivan I. Smalyukh, Oleg Lavrentovich

Chemical Physics Publications

We employ the fluorescent confocal polarizing microscopy to image edge dislocations in cholesteric liquid crystals. Surface anchoring at the bounding plates determines the structure and behavior of defects. Two types of plates set in-plane director orientation but differ in the type of associated anchoring potentials. Plates with strong polar anchoring and nonzero azimuthal anchoring repel the dislocations, while plates with weak polar anchoring and no azimuthal anchoring allow the dislocations to escape through the boundary. To explain the results, we propose a coarse-grained model of cholesteric anchoring.