Temperature effect on spreading of perfluoropolyethers on amorphous carbon films

Abstract

The temperature effect on the spreading behavior of Fomblin Zdol and Z on amorphous carbon surfaces has been studied by scanning micro-ellipsometry. The temperature range explored in this study spans from 26 to 56 °C under 0% relative humidity. The results show that while temperature in general accelerates surface diffusion, it has little effect on the surface conformation of the lubricants. The diffusion coefficient versus film thickness maintains the same shape, only the overall amplitude increases with increasing temperature. The activation energy Ea is found to be relatively insensitive to the lubricant coverage up to one monolayer. The average activation energy is around 37 kJ/mol for Zdol (Mn=2500 g/mol), and around 21 kJ/mol for Z of the same molecular weight. With increasing molecular weight the activation energy increases but the rate of increase is very moderate. More interestingly, the activation energy versus molecular weight curves for Zdol and Z are nearly parallel to each other, suggesting that the interactions between the main-chain and the carbon surface are essentially independent of the interactions between the end-groups and the carbon surface.