Can liquids slide? Linking stability and dynamics of thin liquid films to microscopic material properties

Abstract

Whether a lubricant or a coating wets a surface or not is of great technical importance. Theoretically, it is possible to predict the stability of a thin liquid film on a surface, since it is governed by the effective interface potential. In practice, however, a prediction can be quite cumbersome, since liquids as well as surfaces often consist of numerous components which all influence the effective interface potential. A molecular layer on a substrate's surface like a self-assembled monolayer mainly changes the short-range potential whereas the composition of the substrate below the surface determines the long-range interactions such as the van der Waals potential. The interplay of short- and long-range interactions, including the dielectric properties of all layers in the case of van der Waals interactions, governs the stability of a liquid film. If the film is not stable, distinct rupture mechanisms can be observed causing characteristic film morphologies: spinodal dewetting and dewetting by nucleation of holes, which both entail liquid flow and reveal new routes to study microscopic parameters such as the hydrodynamic boundary condition at the solid/liquid interface. A rather old question turns out to become very important again: Can liquids slide? The article links stability and dynamics of thin liquid films to microscopic material properties and, moreover, describes their experimental access.