THEORY OF NEMATIC LIQUID-CRYSTALS

Theories of nematic liquid crystals are briefly reviewed, and the generalized van der Waals (GVDW) theory is analyzed in some detail. In the latter approach, the short-range repulsion is approximated by hard volume exclusion, and the long-range attraction by dispersion interaction, mean-field averaged. It is shown that if the full London dispersion potential is used the anisotropy in the attractive dispersion potential substantially modifies the mean-field potential anisotropy caused by volume exclusion and affects the nematic-isotropic phase transition temperature and the slope of the coexistence curve, statements can be found in the literature to the contrary. Overall the agreement between theory and experiment, however, is poor. A rigorous formulation is presented of the configurational free energy functions in terms of one-particle distribution functions and correlation functions, applicable to any ordered system at arbitrary density, and practical means for improving the GVDW approach to nematic liquid theory are suggested. © 1990.