Abstract
We have measured the polarized infrared (IR) absorption spectra of polyimide films irradiated by linearly polarized ultraviolet (UV) light as a function of the irradiation energy. To analyze the anisotropic decomposition of the polyimide film, we employed an IR absorption band assigned to the C-O-C asymmetric stretching vibration of polyimide. It is polarized along the polymer chain. The IR dichroic difference increases up to 120 J/cm2, and decreases beyond this energy. The dichroic difference is defined by A⊥-A//' where A_⊥ and A//' are the absorbances for the IR light polarized perpendicular and parallel to the polarization direction of UV irradiation light, respectively. The liquid crystal (LC) molecules sandwiched by UV-irradiated polyimide films in the range from 60 to 120 J/cm^2 align homogeneously with the comparable quality to a LC cell made with rubbed polyimide films. We compared the sturface order parameter of polyimide chains in a polyimide film exposed to UV light of 120 J/cm2 with that in a rubbed film. We found that the anisotropy of the polyimide film induced bv UV light irradiation is much smaller than that induced by a rubbing treatment.
