Director orientation at the nematic-phase–isotropic-phase interface for the model of hard spherocylinders

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Abstract
A fluid of hard spherocylinders is studied in the Onsager model adapted to a nonuniform system. The interfacial properties at nematic-phase–isotropic-phase coexistence are considered. It is found that the angle between the director and the normal to the interface is approximately 60° and does not depend on the length-to-width ratio L/D of the spherocylinder. The nematic-phase–isotropic-phase surface tension, however, tends linearly to zero as D/L→0. It is also argued that the anisotropic hard-core repulsion favors the perpendicular alignment at the nematic free surface. The results concerning the tilt angle are in good agreement with experimental studies for nCB (n=5,6,7,8) [(4-n-alkyl-4’-cyano)biphenyl].