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.
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