Dielectric properties of a PMMA/E7 polymer‐dispersed liquid crystal

Abstract

AbstractDielectric measurement on a polymer‐dispersed liquid crystal (PDLC) has been carried out in the frequency range from 10 Hz to 1 MHz and over the temperature range from 100 to 330 K. The PDLC sample was prepared by thermally induced phase separation of a 50% mixture by weight of commercially available liquid crystal E7 with PMMA and was sandwiched between two indium tin oxide glass plates separated by 40 μm spacers to form a “window.” The dielectric spectrum at low temperature (220–250 K) shows two distinct relaxation processes. Which occur at about 5 K lower than those in pure E7 having Tg ≈ 209 K. From differential scanning calorimetry data, the nematic transition of LC droplets in the PDLC is at 258 K, about 6 K lower than that of pure E7. The Maxwell‐Wagner effect has been observed in the low‐frequency side as the temperature increases from 280 to 320 K. At room temperature, the loss peak associated with the Maxwell‐Wagner effect shows an amplitude dependence with excitation level but no frequency shift. The effect of different concentrations of E7 in PDLC samples at a given temperature shows the 50% mixture has the “fastest” relaxation frequency in such a dispersed heterogeneous system. © 1992 John Wiley & Sons, Inc.