Mechanical Theory for Nematic Thin Films

Abstract

A mechanical model that describes the stability and structure of thin nematic liquid crystal films between two different isotropic fluids is presented. The model provides expressions for the structural disjoining pressure and the generalized Young−Laplace equation and is used to analyze the film as a single membrane and as two separate interfaces (microscopic model). The model is used to find expressions for the film tension (membrane model), the two film surface tensions (microscopic model), the contact angles of the film with the meniscus, and the film spreading coefficient. Asymmetric single-component nematic liquid crystal films are found to be stable because orientation gradients generate positive disjoining pressures. The disjoining pressure in nematic films scales with the inverse of the film thickness square, and this scaling produces an ordering of the surface tensions, such that the single-membrane film tension is greater than the two interface film tensions (microscopic model), which in turn ar...