A Calorimetric Study of Polymer-Dispersed Liquid Crystals: Cure Energetics and Kinetics

Publisher Website
Google Scholar
Abstract
Polymer-dispersed liquid crystal (PDLC) films are formed by the phase separation of liquid crystal (LC) microdroplets from a polymer matrix during cross-linking (cure) of the matrix. Thus, studics of the cure energetics and kinetics of PDLCs provide insights into the mechanisms of their formation. We have carried out such studies for PDLCs cured in two different ways. We have measured the heat released during cure (ΔQ cure) and the time constant for the cure process (T cure) as a function of cure temperature (T cure) for two thermally-cured and four UV-cured systems. The heat of cure for both types of systems exhibits similar behavior: ΔQ cure goes through a broad maximum at a value of T cure where the degree of matrix cure is greatest. On the other hand, the behavior of the cure time constant differs for the two systems: T cure for thermally-cured PDLCs decreases monotonically with temperature, whereas that for UV-cured PDLCs exhibits a minimum. Both quantities are of importance for optimization of PDLC elcctro-optic properties. ΔQ cure is proportional to the degree of matrix cure and therefore a measure of the extent of phase separation of LC from the matrix; T cure plays a role determining liquid crystal microdroplet size.