Application of RF Argon Plasma to Enhance Hydrophobic Properties of Fluoropolymer Pre-deposited Paper

Abstract

Tetrafluoroethane (TFE) pre-deposited paper substrates were exposed to an inert gas (argon) plasma environment in order to convert the hydrophilic to hydrophobic surfaces via grafting and/or cross-linking of the fluorinated layer on the surface of paper, while also improving coating uniformity. The XPS spectrum indicates changes in the nature and relative ratios of the surface functionalities. The application of 300 W RF-power argon plasma (at 10 min and 300 mTorr) created a very highly hydrophobic character (water contact angle, = 120°). A typical high resolution (HR) C1s XPS spectrum of argon-plasma treated TFE pre-deposited paper contains four distinct peaks at 285 (C–C), 285.7 (C–CF), 286.7 (C–O and C–CF2) and 291 eV (CF2–C) binding energies. The C1s region indicates narrowing of the spectrum and complete removal of the CF3–CF (292.5 eV) peak. This change in the shape of HR C1s spectrum also indicates loss of fluorine from the TFE pre-deposited paper with argon exposure compared to only TFE pre-deposited paper. The high-energy argon ions appear to etch the uppermost region, leading to micro-roughening of the paper surface. AFM micrographs reveal re-arrangement of the paper surface with argon plasma exposure. The water absorption of paper coated with TFE alone only decreased by 1.3%. However, after argonplasma treatment of the TFE pre-deposited paper, the water absorption was reduced aproximately by 22% compared to virgin paper.