Spreading and two-dimensional mobility of long-chain alkanes at solid/gas interfaces.

Long-chain n alkanes on solid surfaces can form partially wetting liquid alkane droplets coexisting with solid multilayer terraces. We propose a diffusivelike alkane flow between terrace edge and droplet perimeter through a molecularly thin "precursorlike" film. Depending on the (uniform!) sample temperature, either droplet or terrace edge are not in thermodynamic equilibrium. This leads to a chemical potential gradient, which drives the reversible alkane flow. The gradient can be adjusted and calculated independently from the phenomenological diffusion coefficient.