Mechanical theory of structural disjoining pressure in liquid crystal films

Abstract

A mechanical theory of structural disjoining pressure in nematic liquid crystal films is developed based on Laplace's interfacial stress balance equation. Identification of the interfacial stresses in nematic liquid crystal interfaces leads to two contributions to the structural disjoining pressure. It is shown that tensor order parameter gradients across the film give rise to bulk Ericksen stresses, whose normal component results in a disjoining pressure that tends to stabilize the film. In addition, tangential gradients in the tensor order parameter give rise to gradients in interfacial bending stresses whose normal component results in a film pressure that may be disjoining or conjoining. Phenomenological expressions for the two structural disjoining pressures are obtained using the classical equations of liquid crystal bulk and surface elasticity.