We have used an AFM technique to study the interaction forces between silica glass and polypropylene in aqueous NaCl solutions in order to investigate the existence and properties of any solvation forces which might be generated specifically by the combination of a hydrophilic and a hydrophobic surface. The forces observed were found to be well-described by DLVO theory and indicate that the interaction between these substrates does not generate any significant solvation effects. The low, pH dependent negative charge detected on the polypropylene surface was most likely due to the adsorption of bicarbonate ions from solution onto the low density of carbonyl groups formed by oxidation of the polymer surface.