Influence of atmospheric pressure dielectric barrier discharge on wettability and drying of poly(ether-ether-ketone) foils

Wettability and water droplet drying dynamics on poly(ether-ether-ketone) (PEEK) foils treated by atmospheric pressure air dielectric barrier discharge (DBD) has been investigated. It has been found that plasma treatment causes significant increase of PEEK wettability that is predominantly connected with alterations of its chemical composition (oxidation) induced by DBD plasma. The hydrophilization of PEEK surface was not temporally stable and substantial increase of water contact angle up to 67° was observed with increasing storage time, which is consistent with loosening of polar groups as confirmed by means of XPS. Characteristic restoration time of the contact angle was 6.7 days. Furthermore, a large alteration of the dynamics of water droplets drying on PEEK after the plasma treatment was also observed: whereas for untreated PEEK three drying phases were clearly distinguishable, the phase of constant contact angle disappeared in the case of PEEK exposed to the atmospheric pressure air plasma. In spite of substantial decrease of PEEK wettability with storage time the constant angle phase didn't appear within 51 days after the plasma treatment. As a result of this plasma treated and aged PEEK exhibits much higher water contact hysteresis as compared to untreated PEEK. This effect may be explained by the formation of randomly distributed nanostructures on PEEK surface exposed to DBD plasma that increase the spatial heterogeneity of the PEEK surface and enhance droplet pinning during its drying.