Surface modification of stainless steel using a radio-frequency generated atmospheric pressure plasma

Atmospheric pressure plasma alters the surface properties of a material while leaving the bulk characteristics unchanged. The free radicals in the plasma cause an increase in the hydrophilicity of a material’s surface. This treatment has been shown to enhance adhesion of coatings. However, there is still a need to understand the mechanism. By utilizing an atmospheric pressure plasma on stainless steel surfaces, a change in surface energy was observed. The plasma was produced with a Surfx technologies reactor-A using a mixture of He and O2 gases. The longevity of the treatment, as well as the surface energy changes as oxygen flow rate changes between 0.1 L/min and 0.35 L/min, were measured using the contact angle technique.  The data shows that a 5-second plasma treatment at an oxygen flow rate of 0.20L/min results in the lowest contact angle. The longevity measurements show that 6 hours after a 1-minute treatment, the sample retains a 35% higher surface energy compared to the control. Emission spectra from the plasma were collected and show that more reactive species are present at lower oxygen flow rates. The results indicate the potential of plasma for stainless steel surface modification as well as demonstrate correlation between ROS concentration and the surface energy.