FREE-RUNNING DROPLETS

We present a detailed study of an original spreading behavior observed with nonvolatile droplets containing surface-active agents: The droplet moves spontaneously on the surface with velocities on the order of a few centimeters per second. For small droplets, this self-supported motion may be interpreted in terms of capillary models, which gives precise information about the reaction mechanism that occurs at the surface. For large droplets, gravity intervenes and we observed an important change in the profile of the droplets and different spreading regimes.