THERMODYNAMIC ANALYSIS OF REACTION-INDUCED PHASE-SEPARATION IN EPOXY-BASED POLYMER-DISPERSED LIQUID-CRYSTALS (PDLC)

The Flory-Huggins theory for the free energy of mixing in isotropic ph ases, in conjunction with the Maier-Saupe theory for phase transition of a nematic liquid crystal, was applied to a diepoxide-diamine-liquid crystal blend in pre-and post-gel stages. The analysis was performed taking the distribution of polymeric species into account at any conve rsion level. In the post-gel stage, the elastic energy contribution wa s included in the free energy expression. Cloud-paint and shadow curve s, characteristic of isotropic-isotropic and nematic-isotropic equilib ria, were generated in temperature versus composition coordinates cove ring the whole conversion range. Experimental results for the isotropi c-nematic transition could be reproduced by numerical simulation, usin g an interaction parameter inversely proportional to temperature and d ecreasing with conversion. The thermodynamic analysis can be used to c ontrol the morphologies of polymer dispersed liquid crystals. (C) 1997 Elsevier Science Ltd.