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Srinivasarao, Mohan

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Author: Kumar, Satyendra ×

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    Homeotropically aligning phase separated columnar structures for fabrication of flexible electrooptical devices
    (Georgia Institute of Technology, 2011-11) Acharya, Bharat R. ; Choi, Hyunchul ; Srinivasarao, Mohan ; Kumar, Satyendra
    A method of achieving homeotropic alignment of liquid crystals (LCs) by ultraviolet light induced phase separation of LC from its mixture with photo-curable pre-polymer is reported. Vertical polymer columns and micro-fibrils developed during the phase separation promote homeotropic alignment of the LC director (i.e., alignment perpendicular to the LC-substrate interface), suitable for devices based on LCs possessing negative dielectric anisotropy. These vertical structures extend between two substrates and permit the fabrication of highly flexible electro-optical devices with high contrast coupled with fast response times. This simple single-step technique eliminates the need for the traditional polymer alignment layer pre-deposited on substrates. (C) 2011 American Institute of Physics. [doi:10.1063/1.3663966]
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    Raman Scattering Study of Phase Biaxiality in a Thermotropic Bent-Core Nematic Liquid Crystal
    (Georgia Institute of Technology, 2010-07) Park, Min Sang ; Yoon, Beom-Jin ; Park, Jung Ok ; Prasad, Veena ; Kumar, Satyendra ; Srinivasarao, Mohan
    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 < P-200 > and < P-400 >, and biaxial order parameters < P-220 >, < P-420 >, and < P-400 >, 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 < P-220 > increasing to similar to 0.22 before a first order transition to the smectic-C phase, upon cooling.
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    Nematic biaxiality in a bent-core material
    (Georgia Institute of Technology, 2010-05) Yoon, Hyung Guen ; Kang, Shin-Woong ; Dong, Ronald Y. ; Marini, Alberto ; Suresh, Kattera A. ; Srinivasarao, Mohan ; Kumar, Satyendra
    The results of a recent investigation of the nematic biaxiality in a bent-core mesogen _A131_ are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at _149 °C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on 13C chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149 °C. Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le et al. _Phys. Rev. E 79, 030701 _2009__.