Shape-Regulated Motion and Energy Conversion of Polyelectrolyte Membrane Actuators.

Smart actuators hold great potential in soft robotics and sensors, but their movement at the fluid interface is less understood and controlled, hindering their performances and applications in complicated fluids. Here an ethanol-containing polyelectrolyte actuator is prepared that demonstrates excellent actuating performance via the Marangoni effect. These actuators exhibit enduring (17 min), repeatable (50 cycles), and autonomous motion on the water surface. More importantly, the motion of actuators are dependent on their shapes. Polygonal actuators with more edges exhibit round motion attached to walls of containers, while the actuators with few edges move randomly. On the basis of this property, the circular actuators can pass through pipe bends with S-shaped complex geometry. These unique advantages lend the actuators to successful applications in wireless sensing (standard 0-5 V level signals) for locating obstructions inside invisible pipes and continuous energy harvesting (7700 nC per cycle) for micro mechanical energy.