Introduction

Wetting and de-wetting of surfaces by a liquid are fascinating phenomena of great importance for scientific and technological problems including the self-protection of living organisms, the production of microstructures, as well as the integrity and uniformity of decorative, lubricating and protective coatings and the prevention of fogging. Wetting is influenced by short-range forces, such as hydrogen bonding and donor/acceptor interactions, and by long-range dispersion forces. Depending on the relative strength of these forces, one can observe de-wetting, complete wetting or partial wetting. In the first case, the liquid forms lenses co-existing with the bare surface. In the second case, any amount of liquid applied to the surface will spread out as an even layer with a thickness given by the volume of the applied liquid per area of the surface. In the last case, the competition between favourable short-range forces and unfavourable long-range forces gives rise to the formation of a wetting layer of limited thickness, which often is a monolayer but may in principle have any thickness, that co-exists with lenses formed by excess of the liquid. While most of us are familiar with the technological importance of wetting of solid surfaces, it is worth noting that the wetting of liquid surfaces is technologically important as well, e.g. for the production of thin uniform sheets of material in float cast processes or in the context of slowing down the evaporation of water from open reservoirs in arid regions.