Novel plasma approach for the synthesis of highly fluorinated thin surface layers

SF6-RF-plasma environments were employed for the generation of SF6-oxygen-scavenger species, and used for the synthesis of thin highly fluorinated paper, poly(acrylic acid) (PAA), polyethylene (PE), plasma-oxidized polyethylene (OxPE), and poly(vinyl alcohol) (PVA) surface layers. The concentration of fluorine atoms in the SF6-plasma was monitored using actinometry. The relative surface atomic concentrations and the surface characteristics of the plasma-modified substrates were evaluated using electron spectroscopy for chemical analysis, contact angle goniometry, and atomic force microscopy. It was demonstrated that the plasma-produced SF,, species initiate simultaneous intense surface fluorination and oxygen extraction mechanisms, and that -C-O, -C=O, and -COOH functionalities are converted into -CF, -CF2, and -CF3 groups, respectively. Contact angle (CA) investigations indicate that longer plasma exposure times result in very high, stable contact angle values. It is suggested that the low stability in time of CA values for the paper samples can be related to the porous nature of the substrates and macromolecular motion. The results of these investigations open up novel ways for the plasma-enhanced synthesis of thin membrane structures with dissimilar surfaces, which might play a significant role in the area of membrane-assisted catalysis (e.g., Nafion-type structures). It is also suggested that preoxidized polymer surfaces might lead to more efficient and uniform surface fluorination processes under SF6-plasma environments in comparison to their non-oxidized counterparts. By selecting plasma-enhanced oxidation reaction mechanisms, which selectively result in the formation of -C=O and -COOH groups, novel routes open up for the synthesis of CF2- and CF(3-)bearing surface layers.