Surface characterization of atomic oxygen beam-exposed polyimide films using contact angle measurements

Polyimide surfaces exposed to simulated low Earth orbit space environment, i.e., under hyperthermal atomic oxygen bombardment, were characterized by u sing atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The surface analytical results showed that the roughne ss and the O/C ratio at the atomic oxygen-exposed polyimide surface increas ed with increasing atomic oxygen fluence. The advancing and receding contac t angles decreased with increasing O/C ratios at the polyimide surfaces. Th e Lifshitz-van der Waals component, the acid and base parameters of the sur face free energy of polyimide films were calculated from the contact angles . The base parameter increased with increasing O/C ratio, whereas the acid parameter and the Lifshitz-van der Waals component did not show a remarkabl e change. These analytical results agree with the in situ XPS data showing the formation of surface functional groups due to atomic oxygen exposure. I t was demonstrated in this study that the polyimide surface in a low Earth orbit space environment may become hydrophilic due to the bombardment by at omic oxygen.