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Title:        Influence of thiol caped Silver nanoparticles on Orientatational Order Parameter of Liquid Crystalline material- Optical studies
Authors:   RKNR Manepalli, K. Sivaram, G. Giridhar, P. V. Dattaprasad, P. Pardhasaradhi, V.G.K.M.Pisipati
Abstract:   Liquid Crystals(LCs) are playing a vital role in many fields such as displays, optical switches, Digital Medical imaging etc., because they exhibit isotropic nature like fluid and crystal nature like solid. Especially the molecules of LCs exhibit long range orientation order in Nematic phase which are quiet useful for display purposes. In order to increase the Birefringence anisotropy (δn) and orientation order of molecules of LCs, the author has dispersed different various types metal nanoparticles in low weight concentrations. Because LCs act as tunable solvent for the dispersion of nanomaterials and they are being anisotropic media, provide a very good support for the self assembly of nanomaterials into large organized structures into multiple dimensions. Nanoparticles which are dispersed in LCs can trap ions, which decrease the ion concentration and improve the electro-optical response of LCs. The author has synthesized various metal nanoparticles such as citrate capped/thiol capped Ag and Au nanoparticles from chemical reduction method, ZnO nanoparticles from AutoClave method. These nanoparticles are dispersed in LCs using magnetic stirrer and ultrasonic bath. The synthesized LC nanocomposites are characterized by spectroscopic techniques like X-Ray Diffraction Spectrometric Studies (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopic Studies (SEM), Ultra-Violet Visible (UV-Vis) Spectroscopy etc. The textural determinations of the LC nanocompsites are recorded by using Polarising Optical Microscope (POM) connected with hot stage and camera. These transition temperatures obtained at various phases of these compounds are verified by Differential Scanning Calorimeter (DSC) technique. The transition temperatures obtained from POM are in good agreement with those obtained from DSC. The transition temperatures of nematic and smectic-c phases have reduced with the dispersion of metal nanoparticles. Further in most of the cases the nematic thermal ranges of LCs increased with the dispersion of metal nanoparticles. The intensity of the textures obtained from POM are enhanced by Homomorphic Filtering Technique, Histogram Equalization Techniques etc. The Birefringence anisotropy (δn) values with respect to temperature are determined by using Modified Spectrometer and the values obtained are verified with Digital Birefringence Spectrometer. The order parameter is estimated from the birefringence data without considering any internal field model to liquid crystalline molecule and with the dispersion of various metal nanoparticles. The author found that the birefringence anisotropy as well as orientational order parameter of LC nanocomposites increased by 2-25% which will be very much useful for different display techniques.

Pages:       003-003

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