Surface modification of poly(tetrafluoroethylene) films by low energy Ar + ion-beam activation and UV-induced graft copolymerization

Abstract

Surface modification of poly(tetrafluoroethylene) (PTFE) films by Ar + ion-beam irradiation with varying ion energy and ion dose was carried out. The changes in surface composition of the irradiated PTFE films were characterized, both in situ and after exposure to air, by X-ray photoelectron spectroscopy (XPS). The possible mechanisms of chemical reaction induced by the incident ion beam on the surface of PTFE film included defluorination, chain scission and cross-linking, as indicated by the presence of the characteristic peak components associated with the CF 3,CF, and C(CF 2) 4 species in the C 1s core-level spectra, the decrease in surface [F]/[C] ratio, and the increase in surface micro-hardness of the Ar + ion-beam-treated PTFE films. Furthermore, the free radicals generated by the ion-beam could react with oxygen in the air to give rise to oxidized carbon species, such as the peroxides, on the PTFE surface. Thus, after exposure to air, the Ar + ion-beam-pretreated PTFE films were susceptible to further surface modification by UV-induced graft copolymerization with a vinyl monomer, such as acrylamide (AAm). The graft concentrations were deduced from the XPS-derived surface stoichiometries. The Ar + ion energy and the ion dose affected not only the surface composition of the treated films but also the graft copolymerization efficiency of the corresponding pretreated films.