FTIR imaging studies of a new two-step process to produce polymer dispersed liquid crystals

Polymerization-induced phase separation (PIPS) to produce PDLCs is usually carried out in the one-phase regime to obtain the final dispersion. This PIPS process results in significant residual liquid crystal solubility in the matrix. We investigate a new method to reduce liquid crystal solubility by cooling a homogeneous liquid crystal/precursor mixture into the two-phase regime followed by fast matrix polymerization. The proposed procedure is tested by using a well-studied PDLC system-NOA65 and E7. Liquid crystal remaining dissolved in the matrix is sharply reduced by this method. Residual solubility of the matrix material in liquid crystal domains is also decreased. While maintaining the same phase composition, the method also allows tailoring dispersion size according to needs as opposed to the invariable correlation between droplet size, solubility, and polymerization rate inherent in the classical PIPS methods. This general methodology could be usefully applied to other systems. FTIR imaging, combined with statistical methods, is shown to be an extremely valuable tool for determining phase composition in multiphase systems.