Self-Propulsion of Liquid Marbles: Leidenfrost-like Levitation Driven by Marangoni Flow

Self-propulsion of liquid marbles filled with aqueous alcohol solutions and placed on a water surface is reported. The characteristic velocity of the marbles is ca. 0.1 m/s. The phenomenon of self-propulsion is related to the Marangoni solutocapillary flow caused by the condensation of alcohol, evaporated from the liquid marble, on a water surface. The Marangoni flow in turn enhances the evaporation of alcohol from the marbles. Addition of alcohol to the water supporting the marbles suppresses the self-propulsion. The propulsion of liquid marbles is mainly stopped by water drag. The velocity of the center of mass of the marbles increases with an increase in the concentration of alcohol within the marble. The self-propulsion velocity of marbles is independent of their volume. Self-propulsion was not observed when marbles were placed on a glycerol surface.