jrups

Journal of Research Updates in Polymer Science

Peculiarities of The Orientational State of Liquid-Crystal Completely Aromatic Thermotropic Copolymer
Pages 39-44
V.A. Ryzhov

DOI: http://dx.doi.org/10.6000/1929-5995.2017.06.02.2

Published: 16 June 2017


Abstract: Polarization far-IR spectroscopy has been used to carry out a comparative study of the spectra of granules and fibers of completely aromatic thermotropic liquid-crystal copolymer Vectra A950. The analysis of terahertz polarization IR spectra Vectra A950 showed that in contrast to the mid-IR, dichroic ratio of the absorption bands in the spectra of fibers and granules, substantially different. It is shown that the difference between the value and the orientation order parameter in the samples is determined by and correlated with the intensity of the local dynamics of polymer chains, such as the librational mobility of phenylene and naphthalene rings of the copolymer mesogens. The results suggest the possibility carrying out an independent evaluation of the spectroscopic parameters reflecting the properties of intermolecular interactions in oriented the liquid-crystalline polymers for their low-frequency spectra.

Keywords: Liquid-crystal polymers, far-infrared spectroscopy, local dynamics, orientation order.

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Journal of Research Updates in Polymer Science

Morphological, Thermal and Electrical Properties of (PEO/PVP)/Au Nanocomposite Before and After Gamma-Irradiation
Pages 45-54
E.M. Abdelrazek, A.M. Abdelghany, S.I. Badr and M.A. Morsi

DOI: http://dx.doi.org/10.6000/1929-5995.2017.06.02.3

Published: 16 June 2017


Abstract: Gold nanoparticles (Au NPs) have been successfully biosynthesized by Chenopodium murale (C. murale) leaf extract. Au NPs were incorporated within polyethylene oxide (PEO)/polyvinyl pyrrolidone (PVP) polymer blend by casting method. Scanning electron microscope (SEM), Differential scanning calorimetry (DSC), and DC electrical resistivity were used to investigate the morphological, thermal, and electrical properties of blend/Au nanocomposite before and after gamma-irradiation at different doses (1, 2, 3, 4 and 5 MR).SEM micrographs confirmed the dispersion of Au NPs within the polymeric matrix due to effect of irradiation process. DSC analysis showed that the thermal stability for irradiated samples was improved as compared with pure blend and its nanocomposite. DC measurements revealed nonlinear behavior for electrical resistivity versus temperature. The electrical resistivity values for blend/Au nanocopmosite and its high irradiated samples were less compared to pure blend.

Keywords: Gamma-irradiation, Au NPs, SEM, DSC, electrical resistivity.

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Journal of Research Updates in Polymer Science

Anisotropy Enhanced Phase Separation in Polymer Dispersed Liquid Crystals
Pages 55-67
Farida Benmouna and Mustapha Benmouna

DOI: http://dx.doi.org/10.6000/1929-5995.2017.06.02.4

Published: 16 June 2017


Abstract: Phase separated blends of polymers and low molecular weight liquid crystals, commonly known as polymer dispersed liquid crystals in short PDLCs, are investigated. These materials offer a realm of applications in modern technologies, including sensors, commutable windows, display devices and telecommunication systems. A particular attention is given to the effects of anisotropy of the liquid crystal on the phase behavior under equilibrium and non equilibrium conditions. The theoretical formalism used is based on the lattice model of isotropic mixing, combined with standards theories of nematic and smectic-A orders. Considering the equilibrium phase behavior, we find that the nematic order enhances the polymer / solvent phase separation, and that the osmotic pressure shows substantial changes for relatively small polymer volume fractions. We find that the anisotropy enhanced phase separation is more pronounced for a smectic-A liquid crystal, and the miscibility gap is widened. The kinetics of swelling by nematic LCs is examined using a linear solvent diffusion process, with a rate of swelling directly related to the derivative of the osmotic pressure. An abrupt swelling / de-swelling transition is found, due to overwhelming effects of the anisotropic interaction beyond the threshold LC concentration. Anisotropy enhanced phase separation is also investigated in the method of synthesis based on the polymerization induced phase separation mechanism. We find that the kinetics of separation during early stages of polymerization is faster, due to the anisotropic interaction of the low molecular weight solvent. The kinetics speed up is favored by the long range viscous flow effects due to hydrodynamic interactions. A limited selection of experimental data in the literature is chosen to validate some theoretical predictions obtained from the present formalisms.

Keywords: PDLCs, anisotropy, nematic, phase separation, swelling, kinetics, PIPS.

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Journal of Research Updates in Polymer Science

Editorial: Natural Fiber Reinforced Composites
Pages 1

Sérgio Roberto Montoro


Published: 06 April 2017

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