Correlation between the surface chemistry, the surface free energy and the adhesion of metallic coatings onto plasma-treated Poly(ether ether ketone)

The effects of the surface modification of poly(ether ether ketone) (PEEK) by plasma treatment have been characterized by X-ray Photoelectron Spectroscopy and wettability measurement, while the adhesion of metallic thin films grown by PVD has been assessed by the pull-off test. To investigate the role of the modified surface chemistry on the practical adhesion stress of aluminium thin films, two different plasma technologies were considered: (i) atmospheric pressure plasma and (ii) low pressure microwave plasma. Though on different scales, both of these plasmas under oxidative conditions induced a significant increase of the surface concentration of C=O (ketones) and COO (esters and acidic) functional groups, while C-O-C (ether) groups remained constant. It is shown that after plasma functionalization, when the surface concentration of C=O and COO are above a critical value, a strong correlation appears between the concentration of these polar groups, the wettability and the adhesion potential.