Molecular theory of the isotropic-nematic interface: Hard spherocylinders.

Abstract

The statistical-mechanical theory of inhomogeneous systems is used to derive the grand-potential functional of coexisting isotropic and nematic phases. We employ this result to discuss the isotropic-nematic interface of hard spherocylinders in the square-gradient approximation. Our calculated surface tension is about 40% less than an upper bound derived from a previous, but drastically different, treatment of the interface. The interfacial region is rather narrow and the director of the nematic phase lies parallel to the interface. We compare the formalism to recent experimental studies of the director orientation of nCB's [4-cyano-4'-(n-alkyl)biphenyl], the phenomenological theory of the interface, and postulate the existence of an interfacial polar order parameter. The theory suggests that polar ordering in the interfacial region can cause the director to assume tilt angles between 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} even at the square-gradient level.