Plasma-Surface Interactions at Atmospheric Pressure: Polystyrene Etching and Surface Modification by a Plasma Jet

In this work we studied the interaction of a well-characterized radio frequency (RF) atmospheric pressure plasma jet (APPJ) with polystyrene (PS) as a model polymer. A number of plasma processing parameters, such as treatment distance and angle, feed and environment gas compositions, were investigated by evaluating both polymer thickness and surface chemical composition change after treatment. The effect of different plasma species on polymer surface was compared. We found that for both Ar/O$_{\mathrm{2}}$ and Ar/H$_{\mathrm{2}}$O plasma the etch rate of PS decayed exponentially with treatment distance, whereas surface oxidation increased to a maximum and then decreased. Both the exponential decay constant and oxidation maximum varied with gas composition due to changes in the gas phase species. A surface reaction model based on Langmuir adsorption can explain the observed difference in trends. The reaction rate between incident atomic O or OH radical flux and etched C flux was estimated. Besides, the apparent activation energy (E$_{\mathrm{a}})$ of etching reactions was measured by varying substrate temperature.