Time-dependent changes of surface properties of polyether ether ketone caused by air plasma treatment

Physicochemical and spectroscopic measurements are used to explore the PEEK surface after air plasma treatment. Disappearance of the plasma effect with time is also investigated. The results indicate that significant changes in chemistry of the treated surface occur. The initially obtained modifications gradually fade with time, but the original properties of the untreated surface are not recovered. The effect of air plasma treatment on wetting and energy properties, surface composition and morphology of polyether ether ketone (PEEK) was investigated. The influence of the storage time on the surface properties of plasma‐treated polymer plate was also examined. The properties were determined by advancing and receding contact angle measurements, Fourier transform infrared spectroscopy supported by theoretical spectrum modelling, X‐ray photoelectron spectroscopy and optical profilometry. Three theoretical approaches were used in the determination of the apparent surface free energy of the untreated and plasma‐treated PEEK samples from the measured contact angles of probe liquids (water, formamide, diiodomethane): the contact angle hysteresis method, the Owens and Wendt approach and the Lifsthitz − van der Waals acid–base approach. It was found that air plasma treatment of PEEK causes significant chemical and morphological changes of the polymer surface, which are reflected in the decrease of contact angles from 83.4° to 11.7° for water after 180 s plasma treatment. This is due to the formation of polar functional groups resulting in the increase of the surface hydrophilicity. After plasma treatment the apolar component of the surface free energy practically does not change, while the polar component increases significantly, especially for plates treated for 180 s, from 0 to 19.6 mJ m−2. In addition, the modified PEEK surface is not stable during storage and it acquires more hydrophobic character. © 2016 Society of Chemical Industry