Spreading of perfluoropolyethers on FDTS-coated amorphous carbon surfaces

The spreading properties of mobile perfluoropolyethers (PFPEs) on amorphous carbon surfaces coated with 1 H, 1 H, 2 H, 2 H-perfluorodecyltrichlorosilane (FDTS) islands were investigated using a scanning ellipsometer. The average thicknesses of the FDTS layers varied from 0.5 to 1.4 nm and the film thickness of the mobile PFPEs was about 1.2 nm. We find that a sharp "spike" on the spreading profile occurs and the height of the spike decreases with the spreading time. After partial dip-coating, the initial film boundary of the PFPE on the FDTS islands having a low surface energy cannot spread and the moving film boundary on the bare carbon surface is obstructed by the FDTS island obstacles, which results in the spike formation (i.e., the lubricant buildup) and the retardation of molecular migration. This tendency is remarkable with the increasing average film thickness of the FDTS layer. The spreading is observed at the leading edge of the lubricant front originating from the migration of the lubricant molecules between the FDTS islands by diffusive processes.