Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly(methyl methacrylate)

Abstract

Polymer dispersed liquid crystal composite films were prepared from poly(methyl methacrylate) and nematic liquid crystal E44 by solvent induced phase separation method. In the present investigation we report effect of liquid crystal concentration on the electro-optical and dielectric properties of the composite films. The results were interpreted in terms of phase separation of liquid crystal and polymer, shape and size of liquid crystal droplet, interfacial charge layer effect, liquid crystal loading and miscibility of liquid crystal in the polymer matrix. The miscibility between two phases at interface was investigated by employing Fourier‐Transform Infrared Spectroscopy and differential scanning calorimetry. Morphological study showed that liquid crystal phase is embedded in a spongy poly(methyl methacrylate) matrix and homogeneous distribution increased with increasing E44 content. Electro optical behavior of these composite films under the condition of an externally applied AC electric field (0–200 Vp-p, 50–1000Hz) and wide range of temperature was determined using He–Ne laser (wave length 632.8nm) as a light source. It was found that Poly(methyl methacrylate)/E44 (30/70)wt.% composite has more significant properties than the other concentrations. The performance of all composites showed variations with respect to applied voltage as well as temperatures. Dielectric measurement of polymer dispersed liquid crystals has been carried out in the frequency range from 20Hz to 20MHz and over the temperature range from 24°C to 100°C. The Maxwell–Wagner effect due to interfacial charge accumulation between boundaries of liquid crystal droplets and surrounding of polymer matrix has been observed.