Nematic Ordering of Rod-Like Molecules Interacting via Anisotropic Dispersion Forces as well as Rigid-Body Repulsions

A theory of nematic ordering in liquid crystals has been developed. The method of symmetry-breaking potential and a first-order cluster expansion technique for the partition function are employed. The obtained results agree with those of the Onsager-Isihara (for hard rods) and of the Meiar-Saupe (for dispersion forces) theories in respective limiting cases. The nematic order parameter is calculated as a function of temperature and density of liquids; the calculated values agree very well with the experimental ones on nematic para-azoxyanisole for the pressure range from 1 to 640 ber. The nematic-isotropic transition temperature T c is calculated as a function of the density and shape of molecules (length, breadth and their ratio). The theory provides good explanations, at least qualitatively, of behavior of T c for various homologous series of nematic liquid crystals.