Self-powered macroscopic Brownian motion of spontaneously running liquid metal motors

Abstract

We disclosed the interiorly driven macroscopic Brownian motion behavior of self-powered liquid metal motors. Such tiny motors in millimeter scale move randomly at a velocity magnitude of centimeters per second in aqueous alkaline solution, well resembling the classical Brownian motion. However, unlike the existing phenomena, where the particle motions were caused by collisions from the surrounding molecules, the current random liquid metal motions are internally enabled and self-powered, along with the colliding among neighboring motors, the substrate and the surrounding electrolyte molecules. Through uniformly dissolving only 1 % (mass percentage) Al into GaIn10, many tiny motors can be quickly fabricated and activated to take the Brownian-like random motions. Further, we introduced an experimental approach of using optical image contrast, which works just like the Wilson cloud chamber, to distinctively indicate the motor trajectory resulted from the generated hydrogen gas stream. A series of unusual complicated multi-phase fluid mechanics phenomena were observed. It was also identified that the main driving factor of the motors comes from the H₂ bubbles generated at the bottom of these tiny motors, which is different from the large size self-fueled liquid metal machine. Several typical mechanisms for such unconventional Brownian-like motion phenomena were preliminarily interpreted.

抽象

本文揭示了液态金属马达在碱性水溶液中类布朗运动的机制:固-液界面接触产氢。实验将微量铝箔(质量分数1%)融入GaIn10中,以注射方式产生大量自主运动型微小马达。采用高速摄像仪记录,并基于图像处理量化进行分析。结果表明液态金属马达呈现高速(约4 cm/s)无序的运动模式,我们将其命名为宏观布朗运动。不同于经典布朗现象,宏观布朗运动系由液态金属合金产氢反应、液态金属马达间及其与溶液和基底的多重相互作用所致。此外,通过搭建类似于威尔逊云室的光学平台可以清晰显示液态金属马达产生的氢气轨迹,并证实驱动马达的主要因素来自氢气泡,这与大尺寸液态金属机器主要受表面张力驱动的机制不同。