Polymer-dispersed liquid crystals (PDLCs) can be used in displays. They can be made by polymerizationinduced phase separation in a mixture of monomer and LC. Modification of a photo-d.s.c. with a laser and a photodiode enables the simultaneous measurement of heat Aux and turbidity during polymerization. The heat flux yields the rate and conversion of the polymerization process, whereas turbidity indicates the appearance of a nematic phase. In this way the influence of the LC structure and content, the rate and temperature of polymerization and the cross-linker concentration on the phase separation process have been established for a simple model system. Recording of transmission-temperature curves before and after polymerization reveals the position of cloud points or clearing points in the phase diagram. The use of special cells allows the measurement of transmission-voltage curves on the d.s.c. samples after polymerization.
The morphology, which is important with respect to electro-optical performance, strongly depends on the cross-link density at phase separation.
Secondary phase separation inside LC domains already separated by cooling has been observed with microscopy during fast polymerization, not during slow reaction.