Experimental study of the replenishment of ultrathin liquid perfluoropolyether films on carbon surfaces

Abstract

An experimental study is performed on the spreading and replenishment of ultrathin liquid films of perfluoropolyether Zdol on the same carbon coated disk. Carbon coated disks are partially dip coated, producing a spreading edge of the lubricant film, using Zdol with molecular weights of 2000 and 4000 g/mol. Away from the spreading edge of the film on the same carbon coated disk, the film is scratched by a semispherical slider. An ellipsometer is then used to measure the spreading and replenishment profiles consecutively with time. Diffusion coefficients are calculated from the spreading profiles and then used to simulate the replenishment profiles from the scratched profiles by solving the diffusion equation. The results are compared with the experimentally measured replenishment profiles with time from the same initially scratched profiles. The scratch depths are 1–3 nm for the sample with an initial film thickness of 5–7 nm. The comparison shows that the replenishment of ultrathin liquid films on solid surfaces can be calculated using the diffusion coefficients extracted from their spreading profiles at least for the scratch depth of more than 0.5 nm.