Unconventional locomotion of liquid metal droplets driven by magnetic fields

Abstract

The locomotion of liquid metal droplets enables enormous potential for realizing various applications in microelectromechanical systems (MEMSs), biomimetics, and microfluidics. However, current techniques for actuating liquid metal droplets are either associated with intense electrochemical reactions or require modification of their physical properties by coating/mixing them with other materials. These methods either generate gas bubbles or compromise the stability and liquidity of the liquid metal. Here, we introduce an innovative method for controlling the locomotion of liquid metal droplets using Lorentz force induced by magnetic fields. Remarkably, utilizing a magnetic field to induce actuation avoids the generation of gas bubbles in comparison to the method of forming a surface tension gradient on the liquid metal using electrochemistry. In addition, the use of Lorentz force avoids the need of mixing liquid metals with ferromagnetic materials, which may compromise the liquidity of liquid metals. Most importantly, we discover that the existence of a slip layer for liquid metal droplets distinguishes their actuation behaviors from solid metallic spheres. We investigate the parameters affecting the actuation behavior of liquid metal droplets and explore the science behind its operation. We further conducted a series of proof-of-concept experiments to verify the controllability of our method for actuating liquid metal droplets. As such, we believe that the presented technique represents a significant advance in comparison to reported actuation methods for liquid metals, and possesses the potential to be readily adapted by other systems to advance the fields of MEMS actuation and soft robotics.

Mini/Micro/Nano Scale Liquid Metal Motors

“…The third one does not require the addition of magnetic materials; just pure LM droplets can be propelled by moving a permanent magnet. Shu et al reported an innovative method for controlling the locomotion of MLMTs using Lorentz force [100]. When a permanent magnet approaches the EGaIn droplet, the magnetic flux density B experienced by the droplet increases and induces a current j within the coils, which can be expressed as:…”

Liquid metal motor

“…Until now, electrification of liquid metal has been used almost exclusively to move fluids within otherwise static devices or within electrolytes. For example, CEW has been employed to make pumps (Tang et al, 2014a), mixers (Tang et al, 2014b), microactuators (Khoshmanesh et al, 2017;Li et al, 2020), and tunable antennas (Reichel et al, 2018;Wang et al, 2015), Liquid metals have also been moved using dynamic magnetic fields to induce a Lorentz force (Shu et al, 2018;Yu and Miyako, 2018), chemical reactions to induce unbalanced surface tension (Shu et al, 2020;Tang et al, 2013b;Zhang et al, 2015), electrostatic force (Zhang et al, 2019b), and ultrasound generated acoustic radiation force (Wang et al, 2018).…”

3D Manipulation of Magnetic Liquid Metals

“…In particular, interest in nontoxic gallium-based alloys, such as eutectic gallium-indium alloys EGaIn and Galinstan, has grown owing to their intriguing and unexpected properties, including high flexibility, low viscosity, and excellent fluidity. [1] Consequently, EGaIn and Galinstan have been used for various applications, such as pumps, [2,3] electrical devices, [4][5][6][7][8][9][10][11] actuators, [12][13][14][15][16] metamaterial devices, [17,18] wearable electronics, [19][20][21][22] and soft robotics. [23] Manipulating LMs as flexibly and freely as in the movie Terminator has long been a dream for many scientists across a range of scientific and technological disciplines, ranging from mechanics to biology.…”