Equilibrium phase behavior of polymer and liquid crystal blends

A theoretical framework describing the equilibrium phase behavior of polyme rs and liquid crystals is presented. Linear and crosslinked polymers are co nsidered, and complexities found in the phase properties of systems involvi ng crosslinked networks are highlighted. Effects of the rubber elasticity p arameters in the elastic free energy are found to induce substantial distor tions in: the phase diagram. The Flory-Huggins interaction parameter which governs the miscibility of the mixture in the isotropic state is assumed to be independent of the polymer architecture and modeled either by using a f unction of temperature only or temperature and composition. The thermodynam ic description of the ordered domains is made according to the Maier-Saupe theory for nematic order and its extension to include other ordering proper ties. In particular, the smectic-A order is described according to the gene ralization of the Maier-Saupe theory proposed by McMillan. III the presence of nematogens, the coupling leads to quite different phase properties. In the strong coupling limit, a wide single nematic phase is found. In the wea k coupling, the miscibility gap is much wider. These mixtures are described with mean-field theories of nematogen first developed by Brochard et al. a nd later extended by Kyu et al. This theoretic formalism has been applied s uccessfully to analyze data obtained on several systems including linear an d crosslinked polymer networks, smectic and nematic low molecular eight liq uid crystals (LMWLC), and nematogen mixtures.