Hydrophilic stability of plastic surfaces treated in low- and atmospheric-pressure radio-frequency plasmas

An atmospheric-pressure radio-frequency (RF) corona torch plasma and a low-pressure parallel-plate RF plasma are employed to increase hydrophilicity of polycarbonate and acrylonitrile butadiene styrene surfaces. The contact angle of water for the plastic surfaces is decreased by Ar plasma treatment in any condition, while the surface roughness is decreased, too, unexpectedly. The rate of decrease in contact angle versus treatment time in the atmospheric pressure plasma is about an order of magnitude higher than that in the low-pressure plasma. During postexposure of the plastic surfaces to ambient air, the contact angle is recovered gradually and saturated at a certain value depending on plasma treatment time. A longer plasma treatment time causes less recovery in contact angle. The results indicate that surface roughening as well as surface functionalization is responsible for improving the recovery characteristic and, hence, the hydrophilic stability.