Effect of Host Polymer Matrices on Electro Optical and Dielectric Behaviour of Polymer Dispersed Liquid Crystal System

Abstract

The effect on the electrical characteristics of poly (methyl methacrylate) (PMMA) and poly (methyl methacrylate – co – butyl acrylate) (PMMABA) containing liquid crystal (E8) as dispersed material, is investigated in terms of electro optical and dielectric relaxation spectroscopy (DRS) technique. This polymer dispersed liquid crystal (PDLC) composite film is sandwiched between two glass slides with a transparent conductive substrate such as indium tin oxide (ITO). The resulting assembly forms an electro-sensitive material that can be switched from a OFF state to a ON state by the application of an external electric field or thermal ramp. In the present investigation PMMA / E8, PMMABA / E8 and PMMA+PMMABA / E8 composite films of 30/70 wt / wt % were prepared by Solution Induced Phase Separation (SIPS) method. Morphological study showed that homogeneous LC phase is embedded in a spongy – like polymer matrix. Electro optical behavior was determined under the condition of an externally applied AC electric field (0-200Vp-p, 50-1000Hz). DRS has been carried out in the frequency range from 20 Hz to 20 MHz and over the temperature range from 24°C to 75°C.The interfacial charge layer effect and qualitative evaluation of distribution of relaxation time is characterized by Cole-Cole model.