Polymerization-induced phase separation. 2. Morphology of polymer-dispersed liquid crystal thin films

Phase separation in a polymerizing diacrylate/LC mixture is shown to be driven by liquid−gel demixing rather than by liquid−liquid demixing. The structure of the gel strongly influences the initial morphology:  “early” phase separation (at low conversion) produces spherical domains, whereas “late” phase separation (at high conversion) produces nonspherical domains. The higher the conversion at phase separation, the smaller the domains. A new method, simultaneous photo DSC/turbidity measurement, provides the conversion at the appearance of a nematic phase, and optical microscopy shows the development of morphology. A nonspherical droplet shape reflects the inhomogeneous structure of the polymer network. The dependence of the initial morphology on the LC content, temperature of the reaction, and cross-linker content can be explained using conversion−phase diagrams obtained from the Flory−Huggins−Dusek theory.1 The observable part of the demixing process in a model system composed of 4-n-pentyl-4‘-cyanobiphe...