Tailoring the working gas flow to improve the surface modification of plasma-treated polymers

The paper aims to comparatively investigate the plasma-induced effects − under different discharge regimes: stationary and flowing gas (He and He + 0.5%O2) − on the surface properties of four types of polymers, with a distinct structure, degree of oxidation, and functionality. A pulsed dielectric barrier discharge is used to produce homogenous non-thermal atmospheric-pressure plasma for uniform, efficient, reproducible chemical surface processing. The discharge characteristics, specific to each mode of operation, were analyzed in correlation with the changes in the surface characteristics found following plasma exposure. The plasma treatment increases the surface hydrophilization of all tested polymers, regardless of the discharge mode of operation. Nevertheless, the optimum discharge regime for surface functionalization is correlated with the polymer structure and discharge characteristics. Thus, polypropylene and polystyrene present the maximum wettability in trapping gas mode, while poly(methyl methacrylate) and polysulfone, in the flowing gas mixture. The experimental results demonstrate that working in trapping gas mode is advantageous due to enhanced (>15÷40%) incorporation onto the surface of functional groups related to both oxygen and nitrogen species.