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 in sequential steps. At first, a phase diagram of a binary mixture of LC (E63) and epoxy [diglycidyl ether of polypropylene glycol (DER736)] was established to understand their miscibility. Then, the phase-separation temperatures and morphologies of pre-UV-cured films with different equivalent DER736/dicyandiamide (DICY) molar ratios were observed. Finally, the polymerization-induced phase-separation behavior and morphology of the PDLC film were studied by real-time observation while the film was maintained at 130 °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 undissolved DICY particles acted as nucleation agents and were capable of inducing E63 to separate out early.