Squeezing molecularly thin alkane lubrication films: Layering transistions and wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C(3)H(8); C(4)H(10); C(8)H(18); C(9)H(20); C(10)H(22); C(12)H(26), and C(14)H(30) confined between smooth gold surfaces.

We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length.

We obtain good correlation between our theoretical results and wear experiments.