Theory of liquid crystal anchoring at a porous surface

Abstract

Using classical density functional theory (DFT) the effect of bringing a liquid crystal (LC) into contact with a porous substrate or matrix is investigated. The DFT used is a combination of the Onsager approximation to evaluate the excess free energy of the LC fluid and quenched annealed DFT to evaluate the interaction between the fluid and the porous substrate. When the fluid alignment far from the substrate is held perpendicular to its surface there is a thin layer of fluid aligned parallel to the substrate surface for low matrix densities. For higher matrix densities this director deformation propagates into the bulk of the fluid. Consideration of a system without confining walls suggests that for low matrix densities normal alignment is metastable compared to parallel alignment, while for higher matrix densities it is unstable.