Controllable Flow and Manipulation of Liquid Metals

Abstract

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.

Interface of gallium-based liquid metals: oxide skin, wetting, and applications

“…The role of electrochemical oxidation has been reviewed elsewhere and is briefly highlighted here. 106–108 Fig. 8(b) shows the change in effective interfacial tension of EGaIn via electrochemical oxidation in 1 M NaOH solution.…”

Light-Induced Dynamic Manipulation of Liquid Metal Droplets in the Ambient Atmosphere

“…The formed oxide layer with a large surface tension tends to have strong adhesion to almost any solid surface, thereby severely affecting its kinematic behavior and even causing damage to the substrate. − On the other hand, although adding magnetic substances such as iron particles, nanoscale Fe 3 O 4 particles, and NdFeB can assist LM droplets moving in the strong external magnetic field in the air, it still does not solve the adhesion problem to the substrate. Not only does the physical property, like the transformation point, change with the ineluctable contamination, but under this strong driving force, the LM droplets even suffer from the mass loss during the splitting process of two opposite forces between the applied driving force and the adhesion force to the substrate. − Table S1 provides a detailed comparison of the common manipulations of LM droplets . Therefore, manipulating the LM droplets in the ambient atmosphere is still a challenge to better display their characteristics in electrical equipment as well as within biocompatible equipment.…”

“…30−33 Table S1 provides a detailed comparison of the common manipulations of LM droplets. 34 Therefore, manipulating the LM droplets in the ambient atmosphere is still a challenge to better display their characteristics in electrical equipment as well as within biocompatible equipment. Herein, we not only solved the adhesion problem of the liquid metal, but also provided a strong driving force to achieve the flexible manipulation of LM droplets in the air.…”

Photo-Induced Reversible Deformation of Liquid Metal/Azo Polymer Hybrid Nanospheres for Application as Transformable Nanomachine

“…An intriguing aspect of LMs is their ability to exhibit various types of reversible deformation or locomotion upon being subjected to several external stimuli. These external stimuli include electric fields, magnetic fields, chemical fields, light, heat, and mechanical forces. − Among these diverse energy fields, light field can be utilized to control objects in a noninvasive, remote, and contactless manner. − LMs can show an obvious photothermal effect with irradiation of near-infrared (NIR) light. Recently, Zhou and colleagues have reported the NIR light-induced shape morphing of LM nanodroplets by enhanced photothermal effect with polydopamine (PDA) coating .…”