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

Abstract

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.

摘要

室温液态金属因低黏、超高表面张力(约为水的10倍)及高密度等属性, 蕴藏着新奇的物理景象有待认识. 本文发现了一种金属液滴的相互作用机制: 震荡性融合与接触弹射现象. 实验借助注射泵生成金属液滴, 并采用高速摄像仪记录液滴间的接触融合过程. 基于图像处理的量化结果表明: 金属液滴由于具有较小Oh数, 表面张力在双液滴的接触性震荡融合过程中起主导作用; 金属液滴表面的毛细波传播速度随其半径增大而减小; 造成金属液滴出现接触弹射现象的动力学机制部分来源于表面张力波和双电层效应. 这一基础认识丰富了液滴流体动力学的范畴, 同时也为金属液滴的生成、操控乃至流体特性的刻画提供了理论依据.