Infinite self-propulsion of circularly on/dis-charged high-speed droplets

Abstract Self-propulsion of droplets in a controlled and long path at a high-speed is crucial for electrochemical water oxidation, sub-millisecond organic synthesis and programable lab-on-a-chip. To date, extensive efforts have been made to achieve droplet self-propulsion by asymmetric gradient, yet, existing structural, chemical, or thermal gradient cannot last forever. It is equivalent to stating that a long gradient path also cannot sustain the high gradient density to realize the rapid droplet transport. Here, we demonstrate a circularly on/dis-charged mechanism for droplets to achieve the infinite self-propulsion with ultrahigh velocity of meters per second on a superhydrophobic film with positive and negative alternate potential. Two motion styles of the droplets on superhydrophobic films with different potential are proposed. By permutation and combination of these motion styles, droplet can overcome the trade-off between transport velocity and distance. Moreover, the droplets or even filaments can self-propel along the complicated pathways – such as roller coaster (anti-gravity transport), liquid diode, liquid logic gate as well as any patterned trajectory. Being assembled into a microfluidic chip, our strategy would be applied in the field of cell culture, chemical reaction, and diagnostic kit.