Surface Morphology, Molecular Reorientation, and Liquid Crystal Alignment Properties of Rubbed Nanofilms of a Well-Defined Brush Polyimide with a Fully Rodlike Backbone

Nanoscaled films of poly{p-phenylene 3,6-bis[4-(n-butoxy)phenyloxy]pyromellitimide} (C4-PMDA-PDA PI), a well-defined brush polyimide (PI) composed of aromatic−aliphatic bristles set into a fully rodlike polymer backbone (two bristles per chemical repeat unit of the polymer backbone), were studied by atomic force microscopy, optical retardation, prism coupling, and linearly polarized IR spectroscopy before and after mechanical rubbing with velvet fabric, and their liquid crystal (LC) aligning abilities were investigated. Uniform, homogeneous LC alignment was achieved at the rubbed film surfaces of PIs with positively birefringent characteristics. Surprisingly, however, the LC alignment director for this PI is perpendicular to the rubbing direction as well as to the reorientation direction of the polymer main chains. This is the first time that LCs on a PI surface have been induced to align in the direction perpendicular to the rubbing direction, a significant departure from the LC alignment observed for al...