KINETIC-THEORY OF PHASE-SEPARATION INDUCED BY NONUNIFORM PHOTOPOLYMERIZATION

A kinetic model is developed to study the process of phase separation that occurs when a polymer-dispersed liquid-crystal diffraction gratin g is produced by a process of photopolymerization. We find that the ty pe of system produced depends sensitively on the rate of polymerizatio n and on whether the spatially periodic illumination used to produce t he grating is followed by a period of uniform illumination. While the average liquid-crystal concentration is always increased in the region of least irradiation, in some cases small inclusions of liquid-crysta l form by spinodal decomposition at the minima in the irradiating inte nsity, while in others they form at the maxima. The simplest version o f the theory combines the Flory-Huggins and Hillert models of phase se paration. In some circumstances it must be augmented by including the effects of interdiffusion of polymer molecules having different degree s of polymerization. (C) 1996 American Institute of Physics.