Studying Polymer-Dispersed Liquid-Crystal Formation by FTIR Spectroscopy. 2. Phase Separation and Ordering

Polymerization-induced phase separation to form polymer-dispersed liquid crystals (PDLCs) is a complex process involving simultaneous curing and phase separation to form nematic microdomains. Real-time FTIR spectroscopy has been used to simultaneously observe and quantify the curing process using a model systema fast photocurable matrix (NOA65) and a liquid crystal (E7). While the role of FTIR spectroscopy in monitoring chemical changes is well recognized and reinforced for PDLCs, it is demonstrated in this paper that it is also a powerful tool to monitor physical changes (phase separation and nematic ordering). Phase separation was detected during the curing process by a scattering-induced change in the absorbance spectrum of the sample. Nematic ordering could be observed and quantified based on a change in a characteristic band of the liquid crystal. Moreover, the phase separation and the onset of nematic ordering are temporally resolved. The conversion at phase separation decreases strongly with an inc...