DC electric field-driven heartbeat phenomenon of gallium-based liquid metal on a floating electrode

A system for fluid pumping by liquid metal multi-droplets

The transportation and control of microfluidics have an important influence on the fields of biology, chemistry, and medicine. Pump systems based on the electrocapillary effect and room-temperature liquid metal droplets have attracted extensive attention. Flow rate is an important parameter that reflects the delivery performance of the pump systems. In the systems of previous studies, cylindrical structures are mostly used to constrain the droplet. The analysis and quantitative description of the influence of voltage frequency, alternating voltage, direct current voltage bias, and solution concentration on the flow rate are not yet comprehensive. Furthermore, the systems are driven by only one droplet, which limits the increase in flow rate. Therefore, a pump with a cuboid structure is designed and the droplet is bound by pillars, and the flow rate of the pump is increased by more than 200% compared with the cylindrical pump. For this structure, the mechanism of various factors on the flow rate is analyzed. To further enhance the flow rate, a pump system with multi-droplets is proposed. Moreover, the expression of flow velocity of the solution on the surface of each droplet and the relationship between the flow rate, alternating voltage, and the number of droplets are deduced. Finally, the potential of applying the multi-droplet cuboid pump system in drug delivery and analytical chemistry is demonstrated. Additionally, the core of the pump, the droplet area, is modularized, which breaks the overall structural limitations of the liquid metal pump and provides ideas for pump design.

An Oscillation System Based on a Liquid Metal Droplet and Pillars under a Direct Current Electric Field

Gallium-based liquid metal is a new class of material that has attracted extensive attention due to its excellent deformation characteristics and great potential in applications. Based on the deformation characteristics of liquid metal droplets, researchers have developed many oscillation systems composed of gallium indium tin alloy (GaInSn) droplet and graphite, or aluminum-doped gallium indium alloy (Al-GaIn_24.5) droplet and iron, and so on. Rather than the oxidation and deoxidation mechanisms used in previous systems, an oscillation system that can achieve gallium indium alloy (EGaIn) droplet oscillation with the frequency of 0-29 Hz is designed depending on the interactions between the electric field, pillars, sodium hydroxide, and the droplet. The forces on the droplet are analyzed specifically, which have a great influence on droplet deformation. Additionally, the effects of factors such as voltage, the concentration of sodium hydroxide (NaOH) solution, and droplet size on the droplet oscillation are elucidated based on the force analysis, enabling the flexible control of the oscillation frequency and amplitude of the droplet. This work provides a new perspective on the design of oscillation systems and further enhances our understanding of the deformation of gallium-based liquid metal droplets.

Electrically driven heartbeat effect of gallium-based liquid metal on a ratchet

The realization of the liquid metal heartbeat effect shows better controllability under non-periodic stimuli than spontaneous oscillation or periodic stimuli. However, adjusting the liquid metal heartbeat performance, drop spreading area, and frequency, solely by the magnitude of the voltage, has great limitations. Here, we demonstrate that the eGaIn drop can beat inside graphite ring electrodes under DC voltage in alkaline solutions on ratchet substrates. These sawtooth structures provide asymmetric textures which influence liquid metal deformation during the beating of the heart. We achieved heartbeat frequencies from 2.7 to 4.8 Hz, a 100% increase in the tunable frequency range compared to that on a flat surface. The oxidative spreading of the eGaIn drop on the ratchet substrate shows that the drop penetrates into the grooves of the sawtooth structure. Moreover, we investigated the physical mechanisms affecting the eGaIn heartbeat frequency and the influence on the spreading area of the eGaIn drop at various sawtooth sizes and orientations. These findings not only enhance our understanding of droplet manipulation on sawtooth-structured surfaces but also facilitate the design of microfluidic pump systems.

Liquid metal droplet motion transferred from an alkaline solution by a robot arm

The excellent motion performance of gallium-based liquid metals (LMs) upon the application of a modest electric field has provided a new opportunity for the development of autonomous soft robots. However, the locomotion of LMs often appears in an alkaline solution, which hampers the application under other different conditions. In this work, a novel robot arm is designed to transfer the motion of the LM from an alkaline solution in a synchronous drive mode. The liquid metal droplet (LMD) at the bottom of the robot arm is actuated using a DC voltage to provide the driving force for the system. By introducing an end effector at the center of the robot arm, the synchronous motion of the system is replicated and can be applied to different situations. The theoretical understanding of continuous electrowetting (CEW) at the LM interface is explained, and then the motion performance of the robot arm against the function of the applied voltage and driving direction is investigated. Moreover, several applications using this robot arm, such as pattern drawing, cargo transportation, and drug concentration detection, are demonstrated. The presented robot arm has the potential to observably expand the application fields of the LM.

A tripodal wheeled mobile robot driven by a liquid metal motor

As a novel driving concept, the liquid metal motor (LMM) has been regarded as a promising actuator due to its unique traits, such as infinitely variable speed, lack of transmission chain, convenient maintenance, and silence. However, at present, driving devices based on this material are still in the preliminary and rudimentary stage, and representative application examples are scarce. Therefore, an 8-shaped tripodal wheeled mobile robot (WMR) completely driven by a LMM is designed in this study to further prove the practicability of this material. Through combining the Marangoni surface flow on a liquid metal droplet (LMD) caused by an electrochemical reaction and the eccentric torque generated by the change in droplet shape and position, the two independently driven wheels of the mobile robot are actuated at differential moving speeds. Additionally, a matching control module, a cell phone application, and a battery have been developed and added for wireless control of three types of driving functions (moving forward, steering, and stopping). It is expected that this work could further advance the development and application of LMMs and bring new ideas to the design of WMRs.

Desktop-level small automatic guided vehicle driven by a liquid metal droplet

Gallium-based liquid metals (LMs) are a new type of intelligent material, and their ability to move under the action of an electric field provides new opportunities for the design of small flexible vehicles. However, due to the extremely high fluidity of LMs and the poor automatic control ability of LM vehicles, it's still a huge challenge to control the movement of LMs flexibly and accurately. Therefore, in this paper, a small traction vehicle is designed by putting the flexible LM in rigid armor to make the movement more controllable. Moreover, a desktop-level small automatic guided vehicle (sAGV) system is built by using an external control circuit to follow a predetermined trajectory. Firstly, the basic characteristics of the vehicles driven by a LM droplet are simulated and analyzed. Then the effects of different factors on the movement velocity of the vehicles are measured by experiment. Finally, as a preliminary application test, the sAGV system is used to control the vehicles following a specific trajectory and realize the targeted transportation of cargos. The sAGV system designed in this paper can realize the automatic and precise control of the movement of the small vehicle. The current findings will inspire the further construction of complex small operating systems and the realization of accurate control.