Molecular theory on liquid crystalline mixtures

The nematic-isotropic phase transitions in mixtures of rod-like and disc-like molecules are studied by a mean field theory. We consider both attraction and hard-core repulsion for the model molecules, thermotropic phase transitions are found from the isotropic to one of the two types of uniaxially symmetric nematic phases: optically positive N+ and negative N-. On the other hand, biaxially symmetric nematic phase is shown to be always less stable than the uniaxial phase. We predict that re-entrant phase transition occur for the lyotropic system.