Modification, Degradation, and Stability of Polymeric Surfaces Treated with Reactive Plasmas

Abstract

The degradation, modification, and stability of polymeric surfaces exposed to chemically reactive O2 and H2O-vapor plasmas were investigated. Specifically, the effects of these plasmas on etching rate, surface morphology, wetting instability, and fluid-holding capability were studied. Wetting instability is reflected by hydrophobic recovery and can be examined by the Wilhelmy balance method. Although hydrophobic recovery is usually attributed to surface configuration change, there are actually two types: reversible and permanent. Reversible hydrophobic recovery is caused by surface configuration change, whereas permanent hydrophobic recovery is caused by the creation of oxidized surface oligomers. This study distinguishes the two by identifying differences in the shapes of the corresponding Wilhelmy force loops and in the fluid-holding parameter. The presence of surface oligomers was most detrimental to wetting stability and fluid-holding capability but could be controlled via the type of reactive gas, the discharge conditions, and the polymer substrate. In general, polymers most susceptible to O2-plasma etching had the least surface oligomers and vice versa, whereas H2O-vapor plasma suppressed surface oligomers on polymers less susceptible to etching.