The effect of ambient air plasma generated by coplanar and volume dielectric barrier discharge on the surface characteristics of polyamide foils

This study targeted wettability and adhesion enhancement of polyamide (PA) foil surface by plasma treatment at atmospheric pressure. Volume dielectric barrier discharge (VDBD) and diffuse coplanar surface barrier discharge (DCSBD) were applied in ambient air using exposure times 0.25–2 s. Water contact angle (WCA) measurements proved that both plasma sources achieved significant wettability improvement of PA 6 foil surface immediately after treatment. However, the durability of this hydrophilic effect was much more pronounced with the DCSBD, compared to the VDBD. The lowest registered drop of WCA after DCSBD treatment was from the initial 65° to 28°, which even after one month of storage recovered only to 44°. In contrast, the VDBD treatment at similar parameters resulted in the WCA increase from 45° to 54° already after the first day of ageing. The XPS analysis of oxygen-based polar functional groups incorporated onto the treated PA 6 surface proved higher efficiency of DCSBD plasma. Moreover, the degree of surface oxidation was raised by increasing DCSBD's input power. Tape peel test revealed adhesion improvement achieved only with DCSBD, which had a growing tendency with increasing exposure time and input power. SEM did not show any noticeable damage of surface after the applied plasma treatments.