Liquid metal spring: oscillating coalescence and ejection of contacting liquid metal droplets

With pretty high surface tension, the room temperature liquid metal may inherit with unexpected behaviors that conventional fluids could not own. Here, we disclosed the coalescence and ejection phenomena of liquid metal droplets via high-speed camera. It was experimentally found that, when gently contacting (rather than colliding) two metal droplets with identical size together in NaOH solution, oscillating coalescence would happen which runs just like a spring after the interface ruptures and forms capillary waves. For two metal droplets with evidently different diameters, the coalescence induces rather unusual ejection phenomena. The large droplet would swallow part of the small one and then eject another much smaller droplet. Such phenomenon provides a direct evidence for the existence of electrical double layer on metal droplets. The dynamics fluid impacting behaviors were quantified through processing images from the recorded movies, and the basic differences between the liquid metal droplets and that of water droplets were clarified. Theoretical mechanisms related to the events were preliminarily interpreted. The present finding refreshes the basic understanding of the liquid metal droplets, which also suggests potential values of applying such fundamental effects to characterize viscosity, surface tension, electrical double layer of the metal fluids and droplet formations.