COMPOSITIONAL CHANGES IN PLASMA-DEPOSITED FLUOROCARBON FILMS DURING AGING

Plasma polymer coatings were deposited from perfluoro-1,3-dimethylcycl ohexane (PFDMCH) and their composition and surface properties studied by XPS, grazing-angle Fourier transform infrared spectroscopy and cont act angle measurements as a function of time after fabrication as they were stored under ambient conditions for more than 2 years. The spont aneous ambient oxidation of PFDMCH plasma polymers was found to be a m ulti-step process. The rapid initial oxygen uptake, assigned to reacti on between carbon-centred radicals incorporated into the coating durin g deposition and in-diffusing atmospheric O-2, was similar to that of plasma polymers deposited from hydrocarbon-based monomers (alkanes, al kylamines, alcohols), suggesting that the density of radicals incorpor ated during deposition was similar. Subsequently, however, the extent of oxidation was much lower for PFDMCH coatings. This can be attribute d to the lack of availability of hydrogen abstraction reactions, which are important for radical propagation in hydrocarbon-based plasma pol ymers. While XPS recorded a continuous incorporation of oxygen for mor e than 2 years, the air/water contact angles decreased only during the first 2 months and on further storage remained stable. There appeared to be only a small extent of surface restructuring as assessed from t he small depth variations of compositions. The surface was enriched in CF3 groups at all times. (C) 1998 John Wiley & Sons, Ltd.