POLYMERIZATION-INDUCED PHASE-SEPARATION .2. MORPHOLOGY OF POLYMER-DISPERSED LIQUID-CRYSTAL THIN-FILMS

Phase separation in a polymerizing diacrylate/LC mixture is shown to b e 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 doma ins, whereas ''late'' phase separation (at high conversion) produces n onspherical domains. The higher the conversion at phase separation, th e smaller the domains. Anew method, simultaneous photo DSC/turbidity m easurement, provides the conversion at the appearance of a nematic pha se, and optical microscopy shows the development of morphology. A nons pherical droplet shape reflects the inhomogeneous structure of the pol ymer network. The dependence of the initial morphology on the LC conte nt, temperature of the reaction, and cross-linker content can be expla ined using conversion-phase diagrams obtained from the Flory-Huggins-D usek theory.(1) The observable part of the demixing process in a model system composed of 4-n-pentyl-4'-cyanobiphenyl (K15) and tetraethylen e glycol diacrylate (TEGDA) probably proceeds through nucleation and g rowth rather than through spinodal decomposition. The phase diagram of the unpolymerized monomer/LC mixture is also reported.