Theoretical simulation of thermally induced phase separation in a main-chain liquid-crystalline polymer solution

Phase diagrams of main-chain liquid-crystalline polymer (MCLCP) solutions have been calculated self-consistently on the basis of a simple addition of the Flory-Huggins free energy for isotropic mixing, the Maier-Saupe free energy for nematic ordering, and the Flory free energy for chain rigidity of the MCLCP backbone. The calculated phase diagram is an upper critical solution type overlapping with the nematic-isotropic transition. The phase diagram consists of liquid-liquid, liquid-nematic, and pure nematic regions. Subsequently, the dynamics of thermally induced phase separation and morphology development have been investigated by the incorporation of the combined free energy density into the coupled time-dependent Ginzburg-Landau (model C) equations, which involve conserved compositional and nonconserved orientational. order parameters. The numerical calculations reveal a variety of the morphological patterns arising from the competition between liquid-liquid phase separation and nematic ordering of the liquid-crystalline polymer. Of particular interest is the observation of an inflection in the growth dynamic curve, which may be attributed to the nematic ordering of the MCLCP component, which leads to the breakdown of the interconnected domains. (C) 2003 Wiley Periodicals, Inc.