Molecular interactions and interface properties of nematic liquid crystals

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Abstract
Molecular perturbation methods are used to derive an approximate free-energy functional for nonuniform nematic liquids with anisotropic repulsive and attractive intermolecular forces. The free energy is simplified to a Landau–de Gennes form, providing expressions for the elastic constants and surface fields of the latter in terms of microscopic interactions. These expressions are evaluated using the Gay–Berne model potential (GB) between rigid rod-like molecules. Short-range attractive and repulsive components of that potential are found to give similar contributions to the Landau–de Gennes parameters, but these are strongly counterbalanced by long-range attractive contributions. The theory is applied to orientational alignment and nematic wetting at the free liquid–vapor interface. The preferred nematic alignment is predicted to be perpendicular to the interface, due to a weak dominance by repulsive and short-range attractive forces. It is found that wetting by the nematic phase changes from complete to incomplete as the molecular elongation increases.