Unidirectional liquid-crystal(LC) alignment by a linearly polarized ultraviolet light(UV) exposure was examined using two types of polyimide (PI). PI with a fluorene unit incorporated in a side chain showed LC alignment perpendicular to those of conventional PIs, i.e., perpendicular to the rubbing direction and parallel to the exposure polarization of UV. The results of the dichroic ratio measurement of LCcells,UVabsorption spectra,birefringence, infrared absorption spectra, and PI conformation calculations using molecular mechanics suggest that the photodecomposition of PI by UV exposure produces anisotropic van der Waals forces, which align LC along its optical axis.
Applied Physics Letters
Copyright 1998 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Appl. Phys. Lett. 72, 2403 (1998) and may be found at http://dx.doi.org/10.1063/1.121390.
Nishikawa, M.; Taheri, Bahman; West, John L (1998). Mechanism of Unidirectional Liquid-Crystal Alignment on Polyimides with Linearly Polarized Ultraviolet Light Exposure. Applied Physics Letters 72(19) 2403-2405. doi: 10.1063/1.121390. Retrieved from https://oaks.kent.edu/cpippubs/91