Controllable Flow and Manipulation of Liquid Metals

This review summarizes the controllable flow and manipulation of gallium-based liquid metals (e.g., eutectic gallium indium, EGaIn). There are generally only a few ways to handle fluids, but liquid metals offer versatile control due to their properties: 1) excellent fluidity, 2) adjustable surface tension, 3) electrically and chemically controllable surface oxides, 4) metallic electrical and thermal conductivity, and 5) the ability to alloy with other metals (e.g., magnetic particles). These all-in-one properties empower liquid metals to exhibit controllable flow in confined microchannels (steerable flow) and from nozzles (printable flow), and make liquid metals susceptible to various energy fields, including electric, magnetic, electromagnetic, wave, and light fields. Consequently, the flow and manipulation of liquid metals enable intriguing morphological changes (e.g., formation of droplets/plugs, jets, fibers) and controllable motion (e.g., jumping, bouncing, directional locomotion, rotation) of liquid metals with new fluidic phenomena and practical applications such as soft electronics and robotics. This review aims to present a selective framework and provide an insightful understanding for controlling and shaping liquid metals, thereby stimulating further research and generating increased interest in this topic.