Droplet-Based Self-Propelled Miniboat

Self-propelled autonomous devices have huge application prospects in the field of environmental protection and energy. Nonetheless, the requirement of special chemicals or external electric and thermal energy limits their practical application. Here, a green self-propelling method based on Laplace pressure originated from water droplets is reported. First, a triangle-shaped miniboat composed of a superhydrophobic plate with an inclined superhydrophilic pore is fabricated. Water droplets put on superhydrophilic pore pass through the pore and form a jellyfish-like jet, which further propels the miniboat to move spontaneously and directionally. The propelling distance, propelling time, and instantaneous propelling velocity of the miniboat is greatly affected by the pore size and the initial water droplet volume. Then, two types of devices are designed and installed on the miniboat to successively provide small water droplets from the reservoir or rain to realize the continuous and long-distance self-propelled motion. Moreover, a spindle-shaped miniboat with two or four symmetrical and inclined pores is designed. Under propelling by the torque, the spontaneous and continuous rotation motion is also achieved. This finding will open a new avenue for a wide range of applications ranging from a detecting minirobot on the water surface to a power generation device from rain.