Evolution of electro-optical properties of polymer dispersed liquid crystal materials during processing

Polymer dispersed liquid crystal (PDLC) films are interesting materials par ticulary for optical devices. The initial mixture was composed of diglycidy l ether of bisphenol A (DGEBA), polypropylene oxide diamine (Jeffamine D-40 0), and the nematic low molecular weight liquid crystal E7. PDLC films were obtained by combined thermally and polymerization induced phase separation processes initiated by the temperature controlled polycondensation reactio n of DGEBA and Jeffamine D-400. The electro-optical curves of the obtained films strongly depend on the monomer conversion. It was found that both the transmission in the off-state as well as in the on-state decrease with the extent of cure. In addition, threshold and saturation voltages increase fo r PDLC films characterized by higher monomer conversion values. The electro -optical curves obtained for a conversion of approximately 80% exhibit an u nusual behavior. At monomer conversions approaching 100% the transmission v ersus voltage curves show the expected normal mode.