2005 Volume 38 Issue 8 Pages 641-649
In order to predict the behavior of polyimides and to optimize their fabrication, it is important to understand the relationship between polyimide’s structure and their surface properties. The surface properties (water sorption and repellency, adhesion) are closely related to the surface tension of polymer solid. Critical surface tension γC and surface tension γS of a polymer solid have generally been estimated by the contact angle method. BPDA (3,3′,4,4′-biphenyltetracarboxylic dianhydride)–BAPE (1,2-di(4-aminophenoxy) ethane) polyimide was successfully synthesized. Testing liquids, e.g., dispersion, polar, hydrogen bonding liquids were used to measure the contact angle θ whose values were determined by a quantitative imaging system. Unlikely the existed contact angle measurements, our lab-made quantitative imaging system could provide accurate and reproducible values of the contact angles. The critical surface tensions γC were analyzed by a Zisman plot, a Young-Dupré-Good-Girifalco plot, and a log(1 + cos θ) vs log γL plot. The surface tension γS of BPDA-BAPE polyimide was calculated using the geometric mean equation and multiple regression analysis. The Zisman plot is essentially a downwardly convex curve with polar and hydrogen bonding liquids having γC << γL. The calculated values of γSd (a dispersion component), γSp (a polar component), γSh (a hydrogen bonding component), and γS are 29.69, 13.17, 0.25, and 43.11 mN·m–1, respectively. The γS of BPDA-BAPE polyimide is 43.11 mN·m–1 which is 1.05 and 1.14 times higher than those of Kapton® H films, respectively. The polarity of BPDA-BAPE polyimide is 0.311 whose value was located between 0.87 and 1.39 magnitudes of Kapton® H films’ polarity, respectively.
