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ABSTRACT:The electro-optic performance characteristic of polymer-dispersed liquid crystal (PDLC) composite films out of poly(vinyl butyral) (PVB) and nematic liquid crystal (E7) have been studied for a wide range of PVB-E7 composite compositions (20 -70 wt % of E7). Composites were prepared by solvent casting from chloroform at room temperature. A scanning electron microscopy study showed that a E7 phase is continuously embedded in chink-like structure of PVB matrix. Optical transmittance of the composite films (of 60 and 70 wt % loading of E7) under an alternating current (ac) electric field (0-250, V p-p ) and frequency (50 Hz to 1 KHz) were measured employing HeONe laser ( ϭ 632.8 nm). The results indicate that the (PVB-E7) composite exhibits a memory effect. In the memory state, higher transmittance is preserved without applying voltage. The memory state can be erased and changed to the scattering Off-state by heating the film to the clearing temperature of the liquid crystal.

The isothermal crystallization kinetics, the morphology, and the melting behavior of melt‐processed composites of poly(phenylene sulfide) (PPS) with a thermotropic liquid crystalline copolyester, Vectra A950, (TLCP) were studied by differential scanning calorimetry (DSC) and optical microscopy. The crystallization behavior of PPS in PPS/TLCP composites is observed to be highly sensitive to Tc and immiscible TLCP content in the composites. The spherulite growth rate, the overall crystallization rate, and the activation energy of PPS in PPS/TLCP composites are markedly depressed by the presence of TLCP. The analysis of the Avrami kinetic parameters (n and k) indicates that blending of TLCP with PPS causes heterogeneous growth process and nucleation mechanisms. At low Tcs, the PPS crystallization rate is faster than that neat PPS with ≤30 wt% TLCP loading whereas at high Tcs it remains almost unchanged. The analysis of the melting behavior of these composites indicates that the stability of PPS crystals and their reorganization is influenced both by the Tcs and the composite compositions. The sizes and the number of spherulites change a great extent with composite composition with a drop of spherulite rapid growth rate, at constant Tc, with increasing content of TLCP in composites. The analysis based on the Lauritzen‐Hoffmann secondary nucleation theory, using present DSC data, indicates that present data predominantly follow a linear growth trend over a present range of Tcs and PPS crystallization in composites still occurs according to regime II kinetics, whereby multiple surface nuclei form on the substrate with multiple nucleation acts commencing before initially formed growth layer is completed. The fold surface free energy of PPS chains in composites is found higher than that of neat PPS, leading to an average higher work of chain folding and is ascribed to a general development of the PPS chain mobility in the composite melt. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers