Investigation of the photopolymerization-induced phase separation process in polymer dispersed liquid crystal

A novel experimental method involving simultaneous resistivity and transmittance measurements was used to examine the polymerization-induced phase separation process. Measuring the resistivity and transmittance of a polymer dispersed liquid crystal (PDLC) cell allows the polymerization and phase separation to be monitored during the PDLC formation process. To verify the utility of this method, resistivity data were compared with conversion data obtained by photo differential scanning calorimetry (DSC) and FTIR analysis using NOA65 and an NOA65-E7 mixture. The resistivity data of NOA65 (a neat prepolymer without liquid crystals) were identical to the conversion data obtained by photo-DSC and FTIR analysis. However, the resistivity data of the NOA65-E7 mixture (a prepolymer with liquid crystals) differed from the conversion data because the resistivity of the NOA65-E7 mixture was affected by the degree of liquid crystal phase separation and monomer conversion. The photopolymerization was slower and the degree of conversion was higher for the NOA65-E7 mixture than for the neat prepolymer due to dilution and plasticization effects, respectively.