PHASE-BEHAVIOR OF BLENDS OF POLYMERS AND SMECTIC-A LIQUID-CRYSTALS

The phase behavior of blends of polymers and smectic-A liquid crystals (LCs) is investigated using Flory-Huggins and Maier-Saupe-McMillan th eories. Various examples are considered to depict the effects of the a rchitecture and the size of the polymer together with the nature of an isotropic ordering forces on the phase diagram. The strength of these forces is characterized by a parameter a which is directly related to the temperature of the smectic-nematic transition. Three cases are con sidered depending on the value of ct, and the corresponding phase diag rams are constructed. Substantial differences are observed in these di agrams, and the reasons for these differences are discussed. A compara tive study is performed between mixtures of polymers and LCs, where th e polymer is made of linear and crosslinked chains. The LC consists ei ther of molecules with nematic ordering only or of molecules presentin g both nematic and smectic-A ordering. Blends where polymer matrices a re crosslinked networks are also examined. Remarkable properties are f ound in the nature of the phase diagrams for such mixtures. In general , it is observed that the ordering forces favor unmixing with a strong er effect for the higher smectic-A ordering. Spinodal curves are also reported for these mixtures. The effects of fluctuations near the tran sition temperatures are briefly discussed.