The dynamics of reactive wetting on solid surfaces

Hydrodynamic instabilities driven by chemical reactions at the interface between two liquids have been observed long ago, but lead to very complex situations. We focus here on a relatively simpler case, where a liquid reacts with a solid substrate. When the reaction makes the substrate less wettable, running droplets show up: a drop tends to escape from its own trail. We discuss these experiments and related situations: one interesting future possibility is offered by a solid, porous, bead soaked with the reactive fluid: this should roll spontaneously with velocities 1 mm/s. Another sector of interest is stick-slip motions induced by a solid plate which is slowly plunging into a reactive fluid.