Influence of molecular mass on the liquid crystal alignment of photosensitive fluorinated polyester films

Abstract

Photosensitive fluorinated polyesters (polymer‐n) of varying molecular mass M _n (number‐average molecular mass) were synthesized. The thin films formed from polymer‐n samples could induce liquid crystal (LC) alignment after irradiation by linearly polarized ultraviolet light. The LC alignment direction on the irradiated films was investigated in detail by linearly polarized infrared spectroscopy and polarizing optical microscopy. It was found that LC alignment behaviour changed with change in the molecular mass of polymer‐n: irradiated films with lower or higher M _n induced homeotropic or homogenous alignment, respectively. There was no clear morphological anisotropy in these aligned films, as observed by atomic force microscopy. The surface energies of the irradiated films were also measured using the indirect contact angle method, where both surface energy and its polar component increased with increasing M _n. The variation in M _n could be considered as a main reason for varying alignment behaviour.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 60277033, No. 50473040) and the Science Foundation of Jilin Province (No. 20020603, 20050520).