Contact Angles and Alignment of Liquid Crystals on Lecithin Monolayers

Abstract

The mechanism of aligning liquid crystals by surface action of solid substrates was explained in the literature by a thermodynamical model. This model uses the difference of surface energies of the solid substrate and the liquid crystal to determine the orientation of the liquid crystal. In this letter, contact angle measurements found with 2 different nematics on different lecithin monolayer-coated substrates are reported. Decreasing the area/molecule of the lecithin monolayer from 0.8 nm2 to 0.4 nm2 resulted in an increase of contact angle and simultaneously in a loss of homeotropic orientation, which is in contradiction to the proposed thermodynamical arguments.