Studying polymer-dispersed liquid-crystal formation by FTIR spectroscopy. 1. Monitoring curing reactions

W-induced matrix cross-linking is the method of choice to form polymer-dispersed liquid crystals (PDLCs). In this paper, real-time FTIR spectroscopy is applied to study the curing of a model system-a thiolene-chemistry-based prepolymer (NOA65) and its mixtures with liquid crystals. Curing reactions of NOA65 were examined as a function of the film thickness, temperature, and liquid-crystal content. While there was little dependence of the curing behavior on the thickness of the film, the effect of temperature was strong. Curing rates exhibit a maximum around 325 K, while conversions reach a plateau about 20 K higher. The effect of liquid-crystal addition reveals a depression in the conversion. However, compared to the neat matrix, the final conversion was found to be significantly lower only for phase-separating concentrations. The rate of reaction decreased, and the induction period for the onset of polymerizing reactions increased with increasing liquid-crystal concentration. Real-time FTIR spectroscopy is shown to be a viable tool to monitor PDLC formation to optimize curing conditions and characterize the chemical state of components. This provides a basis to allow the morphological structure to be related to observed properties of the film.