From X-ray diffraction experiments, it is observed that on-substrate cured polyimide films are so oriented that the imide chains are preferentially aligned in the plane direction of the films. For films with rigid-rod polyimide, film orientation is especially prominent and decreases significantly as the film thickness increases. The effect of coating thickness on the orientation and ordering of polyimide films is most pronounced in pure pyromellitic dianhydride-p-phenylenediamine (PMDA-PDA) films, slightly less in films with 50% pyromellitic dianhydride-4,4'-oxydianiline (PMDA-ODA) and 50% PMDA-PDA, and relatively insignificant in those with 100% PMDA-ODA. According to the C=O and C-N stretching absorption bands from Fourier-transform infra-red-attenuated total reflectance spectroscopic experiments, imide molecules located near the centre of the film exhibit poorer structure ordering than those near the surface. This reveals why the average film orientation decreases and the corresponding thermal expansion coefficient increases with increase of film thickness.
Посилання на статтю:
Coating thickness effect on the orientation and thermal expansion coefficient of polyimide films / Jwo-Huei Jou*, Peir-Teh Huang, Hui-Chu Chen and Cheng-Neng Liao // Polymer. – 1992. – Vol 33. – P. 967-974.
