The Interaction Forces between Silica and Plasma-Treated Polypropylene Surfaces in Aqueous Solutions.

The interaction forces between silica and plasma-treated polypropylene surfaces in aqueous NaCl solutions have been measured using a scanning force microscope. The measured interaction forces are well described by DLVO theory at large and moderate separation distances. However, at short range (<5 nm) an additional repulsive force is measured, presumably due to solvation of the surfaces. This additional force was not present when the interaction forces were measured between untreated polypropylene and silica under identical conditions. The presence of C-OH groups on the surface of the polypropylene is proposed to account for this additional repulsive force. In addition, the surface potential and charges fitted to the data were much higher than in the untreated polypropylene case. As no ionizable groups are present on either polypropylene surface, the adsorption of bicarbonate ion from solution is proposed to account for the surface charge.