Chemical reactivity between Teflon surfaces subjected to argon plasma treatment and atmospheric oxygen

Abstract

Surface modification of two Teflon polymers, PFA (tetrafluoroethylene and perfluoroalkoxyvinyl ether copolymer) and PTFE (polytetrafluoroethylene), induced by argon plasma treatment using a radio frequency generator and subsequent air exposure has been investigated by x-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Chemical species assigned to peroxy radicals were produced with the development of a heavily cross-linked or branched structure at the surfaces. The dependence of the XPS and ESR spectra on the plasma treatment conditions (treatment time and power) indicated that the formation of the peroxy radicals was closely parallel to the incorporation of oxygen at the surfaces. The analysis of the XPS and ESR spectra suggested that the peroxy radicals can be attributed to two types of oxygen: one bonded to carbon in the multiply cross-linked structures, and the other bonded to carbon arising from the scission of the main chain of the polymer. The former is the most abundant radical and localized near the surface, but the latter in the bulk region. The relative contribution of the two peroxy radicals for PFA differed from that for PTFE, while the surface chemical structures of both polymers were almost the same. The oxygen of the peroxy radicals was eliminated by UV irradiation in vacuum. For PFA UV irradiated in air for a certain time the chain scission peroxy radical was produced without a change in the surface chemical structure.