Liquid microstructures at solid interfaces

Abstract

The propensity of liquid films to bead off poorly wettable substrates leads to a wide variety of liquid structures via mechanisms which are far from being fully understood. In particular, dewetting via unstable surface waves may be driven at least by dispersion forces, electrostatic forces, or by Marangoni-type transport. A hierarchy of dynamical instabilities finally transforms the initial homogeneous film into the final state, consisting of an ensemble of individual, isolated droplets. While these processes of self-organized structure formation are interesting in themselves, it may also be desirable to generate liquid structures in a more well-defined and predictable way. We have therefore investigated experimentally the behaviour of various liquids on substrates, the wettability of which has been laterally structured. The resulting artificial liquid objects display several remarkable properties, both statically and dynamically. Aside from potential applications as `liquid microchips', it is shown how fundamental quantities can be extracted from the shapes of the liquid surfaces, as determined by scanning force microscopy. The three-phase contact line tensions obtained in this way are in fair agreement with theoretical predictions and might help to resolve long-standing debates on the role of wetting forces on the nanometre scale.