FREE-RUNNING DROPLETS

We present a detailed study of an original spreading behavior observed with nonvolatile droplets containing surface-active agents: The dropl et 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 pr ecise information about the reaction mechanism that occurs at the surf ace. For large droplets, gravity intervenes and we observed an importa nt change in the profile of the droplets and different spreading regim es.