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 Cdouble bondO (ketones) and COO (esters and acidic) functional groups, while Csingle bondOsingle bondC (ether) groups remained constant. It is shown that after plasma functionalization, when the surface concentration of Cdouble bondO and COO are above a critical value, a strong correlation appears between the concentration of these polar groups, the wettability and the adhesion potential.