Density functional approach to the theory of interfacial properties of nematic liquid crystals

Abstract

General expressions for the free energy of the nematic liquid crystal in the interfacial region are derived using the density functional approach. The anisotropic part of the surface tension and the coefficients of the Landau–de Gennes theory for the nematic free surface are expressed in terms of the direct correlation function and analytical results are obtained for a reference system composed of molecules with ellipsoidal equipotential surfaces. The assumption of perfect local orientational order is used to account for strong short‐range orientational correlations in the nematic liquid. It is shown that in such an idealized system the molecules can be aligned parallel or perpendicular to the free surface of the nematic, depending on the balance between attractive and repulsive forces. However, the condition of the stability of the nematic phase requires this alignment to be parallel. The possible role of specific intermolecular interactions, which can be very important in real liquid crystals, is also discussed.