Morphology of epoxy/acrylic polymer-dispersed liquid-crystal film in DICY thermal cure

A polymer-dispersed liquid-crystal (PDLC) film was prepared from UV-curable acrylic, thermally curable epoxy, and a liquid-crystal (LC) mixture with a fixed LC content of 40 wt %. The UV irradiation and heat treatments were i n sequential steps. At first, a phase diagram of a binary mixture of LC (E6 3) and epoxy [diglycidyl ether of polypropylene glycol (DER736)] was establ ished to understand their miscibility. Then, the phase-separation temperatu res and morphologies of pre-UV-cured films with different equivalent DER736 /dicyandiamide (DICY) molar ratios were observed. Finally, the polymerizati on-induced phase-separation behavior and morphology of the PDLC him were st udied by real-time observation while the film was maintained at 130 degrees C under the microscope. The results showed that the acrylic network would not affect the phase-separation behavior of the E63/DER736 mixture. In both thermally induced and polymerization-induced phase separations, the undiss olved DICY particles acted as nucleation agents and were capable of inducin g E63 to separate out early. (C) 2000 John Wiley & Sons, Inc.