On‐Chip Production of Size‐Controllable Liquid Metal Microdroplets Using Acoustic Waves

Abstract

Micro- to nanosized droplets of liquid metals, such as eutectic gallium indium (EGaIn) and Galinstan, have been used for developing a variety of applications in flexible electronics, sensors, catalysts, and drug delivery systems. Currently used methods for producing micro- to nanosized droplets of such liquid metals possess one or several drawbacks, including the lack in ability to control the size of the produced droplets, mass produce droplets, produce smaller droplet sizes, and miniaturize the system. Here, a novel method is introduced using acoustic wave-induced forces for on-chip production of EGaIn liquid-metal microdroplets with controllable size. The size distribution of liquid metal microdroplets is tuned by controlling the interfacial tension of the metal using either electrochemistry or electrocapillarity in the acoustic field. The developed platform is then used for heavy metal ion detection utilizing the produced liquid metal microdroplets as the working electrode. It is also demonstrated that a significant enhancement of the sensing performance is achieved by introducing acoustic streaming during the electrochemical experiments. The demonstrated technique can be used for developing liquid-metal-based systems for a wide range of applications.

Liquid Metal Droplet and Graphene Co‐Fillers for Electrically Conductive Flexible Composites

“…In this range, we found that the 30 min sonication results in the highest conductivity of all slurries containing EGaIn droplets and chloroform‐HCl (Figure g). The conductivities of the mixtures depend on both the size and conductivity of the fillers . While the increase of sonication duration generally leads to a decrease in the particle size, it also increases the exposure time of the droplets to the inevitably dissolved oxygen even under N 2 gas protection, resulting in the formation of thicker surface oxide interfacial layers and therefore lower conductivity .…”

“…The conductivities of the mixtures depend on both the size and conductivity of the fillers . While the increase of sonication duration generally leads to a decrease in the particle size, it also increases the exposure time of the droplets to the inevitably dissolved oxygen even under N 2 gas protection, resulting in the formation of thicker surface oxide interfacial layers and therefore lower conductivity . This explains why the samples sonicated for optimum duration of 30 min, with the intermediate mean size distribution of 0.97 µm, show the highest conductivity .…”

Soft Multifunctional Composites and Emulsions with Liquid Metals

“…As a result, these LMEE composites can be engineered to have a unique combination of elastic, electrical, and thermal properties ( Figure ). More generally, LM droplets can be created through a variety of techniques, including molding ( Figure A), use of acoustic waves (Figure B), microfluidic flow‐focusing (Figure C), shear‐mixing (Figure D,E), and sonication (Figure F,G). As shown in Figure , the LM particle size can range from mm scale (Figure A) to tens and hundreds of nm (Figure H).…”

3D Manipulation and Imaging of Plant Cells using Acoustically Activated Microbubbles

“…Acoustics provide a noninvasive and robust transduction mechanism that has been widely used in micromixing, micropumping, particle or cell separation, and manipulation, protein crystal patterning, microfluidic switches, droplet production, drug delivery, and actuation of micro‐ and nanoswimmers . Acoustic wave–induced microvortices around solid structures and bubbles have been used to perform manipulation of small objects .…”