Theoretical Studies of the Isotropic-Nematic Interface

We discuss phenomenological and molecular theoretical approaches to the thermodynamics of isotropicnematic interfaces. Traditional square-gradient theories are inconsistent with the observed anisotropy of the isotropic-nematic surface tension unless the liquid crystal molecules possess up-down symmetry which they manifest as interfacial polar order. Using the Onsager functional for the nonideal free energy of hard spherocylinders, we show that for short spherocylinders, the fourth and higher-order terms in the gradient expansion of the order parameter profiles may also account for the anisotropy of the surface tension. However, these terms have a negligible effect on the isotropic-nematic interfaces of very long spherocylinders to which the Onsager approximation applies asymptotically.