Synergistic effect in liquid metal heartbeat with high-efficiency energy conversion

The phenomenon of liquid metal "heartbeat" oscillation presents intriguing applications in microfluidic devices, drug delivery, and miniature robotics. However, achieving high vibrational kinetic energy outputs in these systems remains challenging. In this study, we developed a graphite ring electrode with V-shaped inner wall that enables wide-ranging control over the oscillation performance based on droplet size and the height of the V-shape. The mechanism driving the heartbeat is defined as a dynamic process involving the transformation of the oxide layer. Through electrochemical analysis, we confirmed three distinct states of the heartbeat and introduced a novel model to elucidate the role of the V-shaped structure in initiating and halting the oscillations. A comprehensive series of experiments explored how various factors, such as droplet volume, voltage, tilt angle, and V-shape height, affect heartbeat performance, achieving a significant conversion from surface energy to vibrational kinetic energy as high as 4732 J m-2 s-1. The increase in energy output is attributed to the synergistic effect of the V-shape height and droplet size on the oscillations. These results not only advance our understanding of liquid metal droplet manipulation but also pave the way for designing high-speed microfluidic pumping systems.