Morphological Control In Polymer-Dispersed Liquid Crystal Film Matrices

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Abstract
Polymer-dispersed liquid crystal (PDLC) films are derived from the polymerization of solutions of liquid crystals (LCs) in monomers. Upon polymerization:a phase separation occurs causing the liquid crystal to separate into discrete droplets. The liquid crystal material within these droplets still retains the electro-optic properties of bulk material. We describe the preparation of PDLC films in which the polymer is derived from a number of photopolymerizable acrylate-based monomers and the liquid crystal is a commercially available mixture with a positive dielectric anisotropy. It was found that the morphology of the resulting PDLC film can be controlled by the composition and concentration of the monomer/liquid crystal solution, the type of photoinitiator, and the rate of polymerization. Two distinct morphologies were observed: (1) A "polymer ball" morphology, in which the liquid crystal droplets were large and irregularly shaped, and (2) a "Swiss cheese" morphology, in which the liquid crystal droplets were small and nearly spherical. Modification of the polymerization mechanism from a chain polymerization to a stepwise polymerization had a dramatic effect on the resulting morphology.

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