Infrared spectroscopic studies of the thermal stability of alignment layers of polarized UV-exposed polyimide films for liquid crystal alignment

Polarized Fourier transform infrared (FTIR) and optical microscopy with crossed polarizer were used to investigate the thermal stability of the alignment layers formed by rubbing and polarized UV (PUV) irradiation on the polyimide (PI) films. The thermal stability of the PUV irradiated PI alignment layer is lower than that of the rubbed PI layer due to the fragmentation reaction of me PI by PUV. We also investigated the alignment of the liquid crystal by rubbing or PUV irradiation. Liquid crystal (LC) molecules align parallel to the predominant orientation of the PI and perpendicular to the PUV irradiation direction.