Surface modification of plasma-pretreated poly(tetrafluoroethylene) films by graft copolymerization

Abstract

Surface modification of poly(tetrafluoroethylene) (PTFE) films by radio-frequency argon plasma treatment as well as by graft copolymerization of the plasma-pretreated films with acrylamide (AAm) has been carried out. X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical composition and structure of the modified film surfaces. XPS results show that mild plasma treatment is sufficient to cause substantial surface defluorination and oxidation. The oxygen functionalities incorporated greatly facilitate subsequent graft copolymerization in the presence of near-UV radiation. Strong plasma treatment, on the contrary, results in considerable cross-linking of polymers on the surface and thus has an adverse effect on the graft copolymerization. In the course of the present preliminary investigation, it was also found that other water-soluble polymers such as polymers of acrylic acid (AAc), the sodium salt of 4-styrenesulfonic acid (NaSS), N,N-dimethylacrylamide (DMAA), and (N,N-dimethylamino)ethyl methacrylate (DMAEMA) are equally susceptible to grafting onto the mildly plasma-pretreated PTFE surface. In all the cases investigated, the results of XPS angle-resolved measurements suggest that the grafted polymer penetrates and becomes submerged or partially submerged beneath a thin surface layer. Contact angle measurements reveal that the hydrophilicity of the PTFE film is considerably enhanced by the surface plasma treatment and that it can be much further improved with graft copolymerization. © 1993 American Chemical Society.