Electro-optical properties of low molecular weight liquid crystal/copolymer mixtures

Polymer dispersed liquid crystal (PDLC) films can be switched electrically from a light scattering off-state to a highly transparent on-state. Mixture s including different amounts of a high molecular weight copolymer and the eutectic nematic low molecular weight liquid crystal E7 were prepared in ac etone which acts as a common organic solvent. PDLC films were obtained by a solvent induced phase separation (SIPS) initiated by evaporation of the so lvent. The optical transmission properties of the obtained PDLC films were investigated as a function of composition, film thickness, and amplitude of the applied AC voltage. The electro-optical curves depend on the liquid cr ystal content and are highly reproducible. The particular properties of the copolymer allow to obtain a strong physical polymer network which in turn leads to well defined films compared to results obtained for other linear p olymer/E7 systems.