GENERALIZED LANDAU-DE-GENNES THEORY OF UNIAXIAL AND BIAXIAL NEMATIC LIQUID-CRYSTALS

The generalized Landau-de Gennes theory for uniaxial and biaxial nemat ic liquid crystals is analyzed using tensor analysis. In this way all terms allowed by symmetry appear in the free-energy expression. This i mproves the quantitative shortcomings of the commonly used theory. It appears that uniaxial nematic liquid crystals are described by 12 inde pendent generalized elastic terms and that biaxial nematic liquid crys tals are described by 48 independent generalized elastic terms. For pr actical purposes, several approximations based on symmetry arguments a re discussed. The theory is applied to describe the variation in order and orientation near a surface. The relevance of the theory to the de bate on the surface elastic constant K-13 is pointed out.