Phase separations and orientational ordering of polymers in liquid crystalsolvents

A mean-field theory is introduced to describe nematic-isotropic phase trans itions and phase separations in binary mixtures of a liquid-crystal molecul e and a semiflexible polymer chain. On the basis of the Onsager model for e xcluded volume interactions, the Maier-Saupe model for orientational-depend ent attractive interactions, and the Flory-Huggins theory for isotropic mix ings, we derive the free energy of the binary mixtures. We examine the co-o ccurrences of the partial orientational ordering of the polymer chains in t he liquid-crystal solvents and the phase separations, depending on the stif fness of the polymer chain and the strength of anisotropic interactions. Th e new phase behaviors, such as nematic unstable regions, nematic metastable regions, a critical solution point in a nematic phase, azeotrope points, a nd triple points, are examined on the temperature-concentration plane. [S10 63-651X(99)06501-0].