Liquid crystals align liquid crystals

Abstract

We have investigated the molecular orientation of a liquid crystal (LC), pentylcyanobiphenyl (5CB), evaporated on a rubbed polymer by means of polarized ultraviolet absorption spectroscopy and surface second-harmonic generation. The results unambiguously reveal that the in-plane anisotropy is diminishingly small before the molecules form a monolayer, although films thicker than one monolayer have a finite in-plane anisotropy. This drastic change indicates that LC molecules on rubbed surfaces do not align well without the influence of the intermolecular interaction of LCs. Actually we confirmed that nonliquid-crystalline butylcyanobipheny (4CB) exhibits no orientation on the rubbed polymer surface regardless of thickness.