Surface modification of polyimide composites by RF plasma and UV/ozone treatments

Graphite-reinforced polyimide composites are being considered for advanced turbine engine applications, which require that the composite be coated with a wear- and oxidation-resistant coating. For this study, the surface properties of PMR-15 and PMR-II-50 composites were examined and modification techniques investigated to improve coating adhesion. RF plasma and UV/ozone treatments were used to modify the surface chemistry of the polyimide composites, and were optimized to increase the surface energy of the polyimide composites, by etching and deposition of SiOx films. Chemical and physical changes of the composite surface were characterized by contact angle analysis and Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR). Both RF plasma and UV/ozone treatments effectively removed surface contaminants and modified surface chemistry as indicated by increased surface energy. PMR-II-50 and PMR-15 composites responded differently to argon plasma etching and UV/ozone etching because of their structures. Films deposited by plasma-enhanced chemical vapor deposition (PECVD), using tetramethoxysilane, were stoichiometrically closer to SiO2 than the films deposited by PECVD using tetraethoxysilane.