Structural Critical Point at the Free Surface of a Nematic Liquid Crystal

Abstract

I discuss simple Landau theory of the free surface of a nematic, including possible polar ordering effects near the surface. It is found that polar surface order favors a perpendicular alignment of molecules at the surface and this may compete with the usual quadrupolar order which favors parallel alignment. At a critical point, the surface symmetry changes from uniaxial to biaxial and there are large pretransitional fluctuations of the tilt angle of the molecules. The possibility of a soft mode associated with the transition is pointed out.