A Droplet-Driven Micro-Surfboard with Dual Gradients for Programmable Motion

Self-propelled autonomous devices have great significance in energy, environment, and biomedical engineering, and thus vast achievements have been made in recent years. However, conventional propulsion often requires special chemicals or external energy, which restricts their practical applications due to environmental pollution and energy waste. In this work, inspired by the fast movement of a water strider on the water surface, a novel type of droplet-driven micro-surfboard (DDMS) was developed via femtosecond laser micro/nano fabrication, which can be driven flexibly in a green-propulsion method. The DDMS was composed of a superhydrophobic sheet with superhydrophilic wedgy grooves. The droplet was put on superhydrophilic wedgy grooves to enter the water and form a jet, further propelling the DDMS to move directionally. Also, a type of actuator with three superhydrophilic wedgy grooves was designed successively to achieve turn direction, which completes the programable motion by adding droplets to the three channels. Finally, an actuator with circular water storage area and a symmetrical vane-like rotating device with two superhydrophilic channels were developed, realizing long-distance and rotational motions. This work provides new insights into pollution-free autonomous devices, and reveals the great potential in the field of micromachines and intelligent systems