Interfacial Origin of Liquid Crystal Anchorage

Abstract

We have tried to find criteria for liquid crystal orientation by solid surfaces physico-chemical concepts. The solid surface is glass with a soap or polysoap monolayer on it or without such a monolayer. We consider the liquid/solid interaction anisotropies mainly for polar and dispersion forces, and steric interactions. INTRO DU CTlON The orientation of ordinary liquid molecules at interfaces is hardly detectable. The use of liquid crystals allows an easy detection of this orientation. In a first paper,' results have been reported using a nematic liquid crystal with negative dielectric anisotropy. In this paper, we compare qualitively liquid crystals with positive and negative dielectric anisotropies oriented by macromolecules. EX P E R I M E NTA L We deposit a soap monolayer on a solid surface and determine the liquidsolid interaction energy. The orientation was determined by enclosing liquid crystal within cells made of two parallel glass slides, and observing them with a microscope between crossed polarisers. Used systems We have been using two liquid crystals, MBBA and 5CB shown i