Selective adsorption of fluorocarbons and its effects on the adhesion of plasma polymer protective coatings

Cathodic DC plasma deposited films have shown promise as intermediate adhes ion and barrier layers for use in the interface engineering of corrosion pr otection systems on various materials. The surface treatment of plasma depo sited trimethylsilane (TMS) films with various post-deposition plasma treat ments can improve the adhesion of various paints to these films, which are usually strongly adhered to underlying substrates. Research into the applic ation of these systems for corrosion protection of aluminum alloys included post-deposition treatments of the TMS films with hexafluoroethane (HFE) pl asmas, which was seen to significantly improve the adhesion of primers. Oxy gen plasma cleaning of the alloy surfaces, prior to deposition of the TMS f ilm, is normally employed to remove organic contaminants. During testing of sample aluminum panels, one batch was processed without the oxygen plasma treatment and exhibited extensive adhesion failures. The investigation of t hese results shows that low levels of fluorocarbon contaminants readily rea ct with the alloy surface and deposit a fluorine containing carbonaceous la yer, which dramatically interferes with the adhesion of the plasma polymer to the alloys, but the adhesion with primer coatings remains tenacious. X-r ay photoelectron spectroscopy (XPS) studies also show that the presence of even low levels of these contaminants in the chamber, during the oxygen cle aning process, is sufficient to induce the conversion of the surface from o xide to a mixture of oxide and fluoride. This conversion is considered detr imental to the corrosion resistance of these systems. (C) 2000 Elsevier Sci ence B.V. All rights reserved.