Morphology and electro-optic properties of polymer-dispersed liquid-crystal films

An attractive way of making polymer-dispersed liquid-crystal (PDLC) films is through photopolymerization-induced phase separation. The electro-optic properties of these films are determined in large part by the size, shape, and packing of the embedded liquid-crystal drops. We explore the relationships between the conditions of phase separation, morphology, and electro-optic properties. A strikingly strong dependence of electro-optic properties on the fraction of liquid crystal in the film is demonstrated and explained by consideration of the phase separation process. Also, confocal microscopy is shown to be a useful, noninvasive means of obtaining three-dimensional information on PDLC morphology. Not only does it provide very clear images of liquid crystalline drops in the film, but unexpected features were revealed. The drops exhibit a morphology much like a polyhedral foam in the films studied. Polymeric filaments inside the drops were observed as well as a drift in the average size of the drops with proximity to the film substrates. All of these features have important consequences for the electro-optic performance of PDLC films.