R. Bhargava et al., Studying polymer-dispersed liquid-crystal formation by FTIR spectroscopy. 1. Monitoring curing reactions, MACROMOLEC, 32(26), 1999, pp. 8982-8988
W-induced matrix cross-linking is the method of choice to form polymer-disp
ersed liquid crystals (PDLCs). In this paper, real-time FTIR spectroscopy i
s 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, an
d liquid-crystal content. While there was little dependence of the curing b
ehavior on the thickness of the film, the effect of temperature was strong.
Curing rates exhibit a maximum around 325 K, while conversions reach a pla
teau about 20 K higher. The effect of liquid-crystal addition reveals a dep
ression in the conversion. However, compared to the neat matrix, the final
conversion was found to be significantly lower only for phase-separating co
ncentrations. The rate of reaction decreased, and the induction period for
the onset of polymerizing reactions increased with increasing liquid-crysta
l concentration. Real-time FTIR spectroscopy is shown to be a viable tool t
o monitor PDLC formation to optimize curing conditions and characterize the
chemical state of components. This provides a basis to allow the morpholog
ical structure to be related to observed properties of the film.