18.4L: Late-News Paper: Microscopic Molecular Reorientation of Alignment-Layer Polymer Surface Induced by Rubbing and Its Effects on Pretilt Angle

摘要

While the macroscopic molecular orientation induced by rubbing has been extensively studied by many different groups, the microscopic molecular orientation has not been investigated. The microscopic orientation, which deals with repeat units of a polymer, functional groups and side chains at the surface, was explored using contact angle measurements, x-ray photoelectron spectroscopy, top-of-flight secondary ion mass spectroscopy, and infrared spectroscopy. In this work, we have discovered that rubbing induces microscopic molecular re-orientation such that polar or dipole functional groups at the surface are oriented out-of-the-plane of the surface and non-polar aliphatic chains are partially oriented toward the bulk of the film. The polar surface induced by rubbing provided a relatively small LC pretilt angle in the case that an alignment layer polymer does not have long alkyl side chains. It is also proposed that LC pretilt angles at a certain rubbing strength are determined by three major factors which are anchoring, electronic and steric interactions between LC molecules and the polyimide alignment layer surface.