Mechanism analysis of PI/PEEK interface bonding properties enhanced by atmospheric plasma treatment: Experiment and DFT calculation

Due to the increase of service temperature, the bond strength of polyimide composite film will decrease significantly, the continuity of the lapped structure is broken. Therefore, this study proposed a double-layer structure consisting of a polyimide (PI) substrate and Polyetheretherketone (PEEK) coating. The PI/PEEK interface adhesion was improved by using atmospheric plasma treatment. The surface wettability, surface chemical structure, surface element analysis, surface morphology and surface roughness of PI films were studied, respectively. The Materials Studio (MS) was used to model the active groups' grafting mechanism after plasma treatment. The results shown that the surface free energy increased obviously from 27.65 mJ/m(2) to 66.93 mJ/m(2). Reactive groups containing oxygen, such as C = O, C-O, were generated on the surface of PI film due to etching and addition reactions during the plasma process. The mechanical properties of PI films had little change after plasma treatment. The inorganic particles on the surface of the PI film were exposed by plasma etching, which would increase the adhesion between the PI film and the PEEK coating. MS simulated the sequence, relative energy change, and energy barrier of the three functional groups, revealing that the reactivity sequence of the three groups was: -OH > -COOH > -CO-.