Atomic-force-microscope study of polymer lubricants on silicon surfaces

Atomic-force-microscope measurements of the forces on a sharp tungsten tip sliding across silicon substrates coated with perfluoropolyether polymers provide insight into how lubricants function at the molecular level. In particular, hydrodynamic lubrication is observed for tip-substrate separation distances as small as a few polymer chain diameters and a relatively small change in the composition of the polymer, namely, the addition of alcohol end groups, greatly increases the load required to compress and squeeze out the polymers from between the sliding surfaces.