Moving droplets on asymmetrically structured surfaces

It is shown theoretically and experimentally that a liquid droplet can move on a surface structured with a locally asymmetric pattern when a breathing of the drop is induced by external means. Two different situations can be envisioned: a drop whose volume is modulated and a drop whose equilibrium c ontact angle is switched between two extreme values. This last case was exp erimentally investigated using electric fields acting on water droplets in castor oil. The main trends of the theory are verified although a quantitat ive analysis would necessitate either a simpler experimental geometry or a more elaborate model. The results are discussed with a miniaturization of t he setup in mind which would have important potential applications in the f ield of integrated analysis systems. [S1063-651X(99)08009-5].