Effect of oxygen on the discharge characteristics of argon doped ethanol plasma jet and its application in surface modification of polyimide films

Abstract Doping a small amount of ethanol gas (EtOH) in argon can change the argon plasma jet from filamentary discharge mode to diffuse discharge mode, and further doping of trace oxygen can significantly enhance the composition and content of oxygen-containing active particles in the argon plasma. Based on this, the discharge characteristics of Ar + EtOH plasma jet under different concentrations of oxygen doping and its effect on the surface modification effect of polyimide (PI) films were investigated in this paper. It was found that the discharge characteristics of Ar + EtOH + O 2 plasma jet deteriorate with the increase of oxygen doping concentration, but the oxygen doping concentration of 0–4000 ppm can still be stable, diffuse and the gas temperature is close to room temperature. Through the water contact angle (WCA) measurement and peel strength test, it was found that when the oxygen doping concentration was 800 ppm, the Ar + EtOH + O 2 plasma jet treatment for 180 s had the best effect on the improvement of surface wettability and adhesion of the PI films, and the WCA was reduced from ∼71.9° to ∼17.6°. At the same time, the peel strength was increased from 122 N m −1 to 418 N m −1 , which is an increase of ∼243%. Combined with the material characterization analysis, it was found that the surface roughness of the PI films was enhanced and more C–O and C=O bonds were grafted on the surface after the Ar + EtOH + O 2 plasma jet treatment. Finally, through the two-dimensional axisymmetric argon-doped ethanol plasma jet hydrodynamic simulation analysis, it was found that when the working gas Ar + EtOH was doped with 800 ppm O 2 , the number density of OH did not change much, but the number density of O 2 − was about 6 orders of magnitude higher than that of the non-doped O 2 . The mechanism that Ar + EtOH + O 2 plasma jet could improve more wettability and bonding of PI films in a shorter treatment time was revealed.