CONTACT ELECTRIFICATION OF CHEMICALLY MODIFIED SURFACES

We have studied charge transfer from a variety of metals to solution-cast samples of polyvinyl-alcohol chemically treated to introduce superficial halogens (F, Cl, Br and I). Even though surface analysis shows that only a fraction of the hydroxyl groups are converted to halogen we find that the chemical treatments change the sign of the charge transfer from positive to negative; moreover, the charge transfer becomes much less dependent on metal work function as a result of the chemical treatment. Just such changes are expected if it is supposed that the Cl treatment (for example) converts the surface of the polymer from polyvinylalcohol to polyvinylchloride, and our experiments thus provide striking support for the opinion, expressed by many workers, that the contact electrification of polymers is intimately connected with their chemical composition. Chemical modification of a thin surface layer may provide a controlled means of adjusting the contact charging properties of a polymer with minimum disturbance of desirable bulk properties.