Critical behavior in anchoring transitions of nematic liquid crystals

Abstract

The adsorption of water onto a crystal surface can result in a first-order transition in the orientation of the director of a nematic liquid crystal spread on top of the surface. Here, we show that coadsorption of two or three chemicals can lead to a phase diagram having first-order transition boundaries, critical lines, and critical points. A simple Landau theory accounts for most of the phenomena we observe. This experiment gives the first direct optical visualization of a two-dimensional system near its critical point.