Publication Details

Yu, Z., Chen, Y., Yun, F. F., Cortie, D., Jiang, L. & Wang, X. (2018). Discovery of a Voltage-Stimulated Heartbeat Effect in Droplets of Liquid Gallium. Physical Review Letters, 121 (2), 024302-1-024302-5.


Chemomechanical effects are known to initiate fluid oscillations in certain liquid metals; however, they typically produce an irregular motion that is difficult to deactivate or control. Here we show that stimulating liquid gallium with electrochemistry can cause a metal drop to exhibit a heart beating effect by shape shifting at a telltale frequency. Unlike the effects reported in the past for mercury, the symmetry-breaking forces generated by using gallium propel the drop several millimeters with velocities of the order of 1 cm per second. We demonstrate pulsating dynamics between 0 and 610 beats per minute for 50-150 μL droplets in a NaOH electrolyte at 34 °C. The underlying mechanism is a self-regulating cycle initiated by fast electrochemical oxidation that adjusts the drop's surface tension and causes a transformation from spherical to pancake form, followed by detachment from the circular electrode. As the beat frequency can be activated and controlled using a dc voltage, the electrochemical mechanism opens the way for fluidbased timers and actuators

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