DIELECTRIC-PROPERTIES OF A PMMA/E7 POLYMER-DISPERSED LIQUID-CRYSTAL

Dielectric 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 mum 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 T(g) almost-equal-to 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.