Spatial Distribution of Wettability in Aluminum Surfaces Treated with an Atmospheric-Pressure Remote-Plasma

The use of atmospheric-pressure remote plasmas (postdischarge) sustained in argon and argon–nitrogen for the treatment of aluminum surfaces has been studied to better understand the underlying mechanisms responsible for cleaning and activating the surfaces. The effect of the gas composition, treatment distance, and speed on the hydrophilicity of commercial aluminum samples has been studied using the sessile drop method to build spatial profiles of the treated zones. In the case of argon–nitrogen postdischarges, neither the distance to the plasma end (2 < z < 6 cm) nor the treatment speed (2500 < v < 7500 m/s) had a significant impact in the spot radius of the treatment, remaining approximately constant around 6–7 mm. This result seems to indicate that the postdischarge experiments a little expansion at the exit of the tube in which the discharge was created but its action can be considered highly-directional. This fact is essential for the possible industrial implementation of the procedure described in this research. These results have been analyzed together with the composition of active species in the postdischarge by using optical emission spectroscopy, revealing that long lived nitrogen species are required to significantly increase the wettability of the aluminum surfaces.