Fluorination of silylated nanosilicas using c-C4F8 radiofrequency plasma

Abstract

The structure of surface layer of octafluorocyclobutane radiofrequency plasma (c-C4F8 rf-plasma) treated fumed silica—pristine and chemically modified with triethoxy-, vinyltriethoxy-, or vinyltrichlorosilane—has been studied by means of FTIR- and X-ray photoelectron spectroscopy as well as temperature-programmed desorption mass spectrometry. The surface layer structure of the silylated nanosilicas after plasma fluorination was found to be defined by the reactivity of the pre-grafted groups. It was revealed that for hydride- and vinyl-silylated silicas at facile (about 15 min) treatment the single fragments with C:F ratio close to 1:1 are attached to surface (as in the case of pristine silica fluorination), whereas a long term (about 60 min) plasma treatment leads to formation of polymeric structures at the surface. Both the nature of pre-grafted groups, capable to be involved in polymerization reaction, and their concentration effect on these polymeric structures. Thus, at surface groups concentration of about 0.5 mmol/g fluorine-enriched polymeric chains are formed, while at twice as little concentration the chains with unsaturated bonds are generated.