Influence of Ar/O$_{\mathrm{2}}$/H$_{\mathrm{2}}$O Feedgas AND N$_{\mathrm{2}}$/O$_{\mathrm{2}}$/H$_{\mathrm{2}}$O Environment on the Interaction of Time Modulated MHz Atmospheric Pressure Plasma Jet (APPJ) with Model Polymers

An Ar/O$_{\mathrm{2}}$/H$_{\mathrm{2}}$O fed time modulated MHz atmospheric pressure plasma jet (APPJ) in a sealed chamber was used to study plasma interaction with model polymers (polystyrene, poly-methyl methacrylate, etc.). The amount of H$_{\mathrm{2}}$O in the feed gas and/or present in the N$_{\mathrm{2}}$, O$_{\mathrm{2}}$, or N$_{\mathrm{2}}$/O$_{\mathrm{2}}$ environment was controlled. Short lived species such as O atoms and OH radicals play a crucial role in polymer etching and surface modifications (obtained from X-ray photoelectron spectroscopy of treated polymers without additional atmospheric exposure). Polymer etching depth for Ar/air fed APPJ mirrors the decay of gas phase O atoms with distance from the APPJ nozzle in air and is consistent with the estimated O atom flux at the polymer surface. Furthermore, whereas separate O$_{\mathrm{2}}$ or H$_{\mathrm{2}}$O admixture to Ar enhances polymer etching, simultaneous addition of O$_{\mathrm{2}}$ and H$_{\mathrm{2}}$O to Ar quenches polymer etching. This can be explained by the mutual quenching of O with OH, H and HO$_{\mathrm{2}}$ in the gas phase. Results where O$_{\mathrm{2}}$ and/or H$_{\mathrm{2}}$O in the environment were varied are consistent with these mechanisms. All results will be compared with measured and simulated species densities reported in the literature.