ISOTROPIC-NEMATIC TRANSITION: LANDAU-DE GENNES VS MOLECULAR THEORY.

Landau-de Gennes and molecular mean-field descriptions of the isotropic-nematic transition are compared using two methods to calculate the order parameter correlation function and showing that corrections due to cubic and quartic terms in the Landau expansion are non-negligible. A comparison of the results with experiment indicates only qualitative agreement. It is also found that the supercooling temperature T* is different from T xi , the temperature at which the correlation length diverges. The fact that the corrections are not small and that the results obtained by the two different methods are inconsistent cast grave doubt on the quantitative validity of the Landau-de Gennes approach in its present form. A numerical way is proposed to establish contact between the meanfield theory and the Landau-de Gennes theory. Results indicate that the two approaches are irreconcilable.