Effect of nematic liquid crystals on optical properties of solvent induced phase separated PDLC composite films

Abstract

In the present article the effect of two different types of nematic liquid crystals on electro-optical and thermo-optical properties of polymer dispersed liquid crystal films are discussed. Composite films composed of polymer poly(methyl methacrylate) and two different nematic liquid crystals E7 and E8 were prepared by solvent induced phase separation technique. Scanning electron microscopy and polarizing optical microscopic results showed that liquid crystal phase is continuously embedded in a sponge-like polymer matrix. The domains of E7 were found slightly larger and more elongated than E8 under the same conditions of preparation. Variation of optical transmission properties of the composite films under the conditions of an externally applied alternating electric field (0-300 Vp-p, 50-1000 Hz) over a wide temperature range was studied using He-Ne laser (wavelength 632.8 nm) as a light source. The experimental results showed that the E7-polymer film has better electro-optical as well as thermo-optical properties as compared to the E8-polymer system. The performances of both the composites improved significantly with increasing temperature. It was found that the physical properties such as viscosity, refractive index and transition temperature of liquid crystals play a major role on the properties and behavior of the polymer dispersed liquid crystal composite films.