Surface modifications of polymers with fluorine‐containing plasmas: Deposition versus replacement reactions

Abstract

Abstract Surfaces of polyethylene; poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), cellulose acetate butyrate, and polyoxymethylene were modified in various cold plasma reactions; feed gases to the plasma reactor were trifluoromethane, hexafluoroethane, and tetrafluoromethane. Using X‐ray photoelectron spectroscopy (ESCA) to characterize the surfaces, it was established that the plasma reactions lead to fluorinated surfaces containing CF 3 , CF 2 , and CF groups, All of these fluorinated surfaces exhibit advancing contact angles (with water) larger than 900. However, differences in the ESCA spectra, weight‐gain/‐loss measurements and scanning‐electron‐microscopy (SEM) photographs reveal that the mechanisms of fluorination in the various plasma environments are markedly different. The CF 3 H gas polymerizes in the gas phase of the plasma and deposits a smooth, fluorinated film on polymers and other substrates. The C 2 F 6 plasma simultaneously etches polymers and polymerizes onto polymer surfaces. The CF 4 plasma etches and reacts with the polymer surface but does not polymerize. For polyoxymethylene, the combined roughening (by etching) and fluorination of the surfaces lead to completely non‐wettable surfaces (water contact angle approximately 180°). The highly non‐wettable surfaces of these two polymers are believed to result from the physical etching and roughening at a very fine scale (approximately five micrometers) while the outermost surfaces are reacting to become highly fluorinated.