Optical anisotropy of flexible polyimide thin films
- PDF / 142,477 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 293 Views
MATERIALS RESEARCH
Welcome
Comments
Help
Optical anisotropy of flexible polyimide thin films Baozhong Li, Tianbai He,a) and Mengxian Ding Polymer Physics Laboratory, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China
Ping Zhang, Fubin Gao, and Feng Jing Changchun Institute of Physics, Chinese Academy of Sciences, Changchun 130022, People’s Republic of China (Received 9 June 1997; accepted 5 November 1997)
Optical anisotropy of thin films of an organo-soluble flexible polyimide based on 1,4bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2-dimethyl-4,40 -methylene dianiline (DMMDA) was detected by a prism-coupler technique. A mechanism is proposed, based on the model of gel film collapse. The degrees of optical anisotropy of the thin films were evaluated via the level of negative birefringence. The residual solvent in the films lessens the levels of negative birefringence so that the residual solvent must be evacuated. The levels of negative birefringence are independent on the solid content of the initial solution, but dependent on the thickness of the films. For a film of 16 mm thick, zero birefringence was achieved, postulated from the dependence of negative birefringence on the thickness of thin films. The relationship between the optical anisotropy and solution properties shows that the degrees of optical anisotropy of thin films on the same scale of thickness depend on macromolecular sizes in their dilute solutions.
I. INTRODUCTION
Polyimides have been widely used in industry owing to their high mechanical, chemical, and optical performance.1 Optical anisotropy of polyimide thin films has been reported.2–4 Chain stiffness contributes to negative birefringence of polyimide thin films mainly.5,6 Stress in polyimide thin films also induces negative birefringence.7 Recently, Coburn and Pottiger8 have given a review about the thermal curing of polyimide films and coatings. They concluded that negative birefringence of polyimide thin films was attributed to molecular alignment in the plane of the coating, resulting from gel film collapse. In the formation of gel film, anisotropic structure is fixed, because of the evaporation of the solvent and the frozen molecular aggregation. In this paper, thin films of an organo-soluble flexible polyimide were studied by the prism coupler technique, and a model is presented to explain the optical anisotropy of thin films of a flexible amorphous polyimide. II. EXPERIMENTAL A. Materials
The organo-soluble polyimide in this work was synthesized by stirring equivalents of dianhydride and diamine in the solvent of N,N-dimethyl acetamide (DMAc), at room temperature with nitrogen atmosphere, until a slight yellow color polyamic acid solution was
fulfilled. In this case, the dianhydride is not soluble in DMAc, and as long as there is no solid left in the solution, it is regarded that polyamic acid solution is obtained. It takes 24 h for triethylamine and acetic anhydride to undertake chemical imidizati
Data Loading...
