Ga-based Liquid Metal Research Articles

Liquid metal fractals induced by synergistic oxidation

Ga-based liquid metal has drawn attention in the field of interface science due to its large deformability. However, the spreading and shaping of liquid metal still remain a huge challenge to be solved owing to its large surface tension. Here, an intriguing synergistic oxidation-driven liquid metal fractal phenomenon was discovered and the general mechanisms were interpreted, which provides a new strategy for manipulating liquid metal. Experimental results demonstrate that the liquid metal placed on the graphite plate exhibited fractal characteristics with the addition of hydrogen peroxide. Here, it is of significance that hydrogen peroxide and graphite plates synergistically oxidize liquid metal. In addition, we predicted that liquid metal fractals can also be achieved on other eligible substrates based on the proposed general mechanism, which was confirmed by relevant experiments. Furthermore, the fractal dimensions of liquid metal fractal pattern were obtained and evaluated, distinguishing the synergistic oxidation-driven liquid metal fractals from the voltage-driven liquid metal fractals. Besides, we initially gave the best concentration range in which dendritic fractals can occur in order to guide practice. The ability to achieve liquid metal fractals promises rich opportunities in freely driving the liquid metal for soft machines and manufacturing the shape-reconfigurable electronic circuits.

Ga-based liquid metal: Lubrication and corrosion behaviors at a wide temperature range

Novel Ga-based liquid metal (GLM) may be a promising coolant and lubricant in the advanced liquid-metal nuclear reactor, due to its excellent physicochemical properties. But the lubrication and corrosion behaviors of GLM over a wide temperature range are unclear, which are vital to the service safety of the nuclear reactor. In this work, a high-temperature T91 steel was chosen to slide against Al2O3 ball in GLM medium and vacuum atmosphere from room temperature (RT) to 800 °C, to clarify this issue. It was found that liquid-metal will decompose and form a Ga-rich film on the contact interface and thus can provide good boundary lubrication at RT and 200 °C. At 400 °C, a Ga-rich film also exists and the steel begins to react with GLM to form nano-FeGa3 crystal, providing the synergistic lubricating effect. At 600 and 800 °C, GLM corrodes severely the T91 steel and various polymetallic intermetallics are formed, counteracting the lubricity of GLM. In addition, the distinct corrosion mechanisms of GLM on the T91 steel at 600 and 800 °C were preliminary studied and proposed, namely, inside-out growth at 600 °C and outside-in dissolution corrosion at 800 °C.

Ga-based liquid metal with good self-lubricity and high load-carrying capacity

Abstract Extreme pressure lubrication is a great challenge for many mechanical systems like bearings and gears. Here, an novel functional material based on Ga-based liquid metal has been applied to successfully lubricate the steel-ceramic sliding pairs at extreme high load (1500 N), which significantly outperforms other liquid lubricants like oil and ionic liquid. Ga-based liquid metal provides a low friction coefficient (0.11–0.23) and wear rate (10−8-10−7 mm3/Nm) of AISI 52100 steel disc (C0.98-1.10Mn0.25-0.45P≤0.025S≤0.025Si0.15-0.30Cr1.30-1.60Fe96.5-97.32, mass %; American Iron and Steel Institute standard) when it slides against Si3N4 balls over a load range 100–1500 N. To elucidating these interesting results, the lubrication mechanisms of Ga-based liquid metal are studied by tribo-surface analysis.

A Liquid-Metal-Based Magnetoactive Slurry for Stimuli-Responsive Mechanically Adaptive Electrodes.

Electrical communication between a biological system and outside equipment allows one to monitor and influence the state of the tissue and nervous networks. As the bridge, bioelectrodes should possess both electrical conductivity and adaptive mechanical properties matching the target soft biosystem, but this is still a big challenge. A family of liquid-metal-based magnetoactive slurries (LMMSs) formed by dispersing magnetic iron particles in a Ga-based liquid metal (LM) matrix is reported here. The mechanical properties, viscosity, and stiffness of such materials rapidly respond to the stimulus of an applied magnetic field. By varying the intensity of the magnetic field, regulation within a factor of 1000 of the Young's modulus from ≈kPa to ≈MPa, and the ability to reach GPa with more dense iron particles inside the LMMS are demonstrated. With the advantage of high conductivity of the LM matrix, the functions of the LMMS are not only limited to the soft implanted electrodes or penetrating electrodes in biosystems: the electrical response based on the LMMS electrodes can also be precisely tuned by simply regulating the applied magnetic field.

A Protective FeGa3 film on the steel surface prepared by in-situ hot-reaction with liquid metal

Ga-based liquid metal may be a novel coolant and lubricant for the steels at high temperature and extreme pressure in the nuclear reactor. It is recently reported that the formation of FeGa3 film may be responsible for the good lubricity of liquid metal, but no proof can clarify this point and its wear behavior is unclear. Therefore, an in-situ FeGa3 film was prepared through the hot-reaction between liquid Ga65In22Sn13 (65% Ga, 22% In, 13% Sn by mass) and T91 steel at 600 °C in this paper. The results indicate that FeGa3 film forms and bonds strongly to the steel surface. It has good mechanical and tribological properties at room temperature, but increases the wear at 600 °C. The finding provides the technical support for the safety service of the steels in the liquid-metal environment and is also a new strategy for protecting the steel.

High thermal conductivity liquid metal pad for heat dissipation in electronic devices

Novel thermal interface materials using Ag-doped Ga-based liquid metal were proposed for heat dissipation of electronic packaging and precision equipment. On one hand, the viscosity and fluidity of liquid metal was controlled to prevent leakage; on the other hand, the thermal conductivity of the Ga-based liquid metal was increased up to 46 W/mK by incorporating Ag nanoparticles. A series of experiments were performed to evaluate the heat dissipation performance on a CPU of smart-phone. The results demonstrated that the Ag-doped Ga-based liquid metal pad can effectively decrease the CPU temperature and change the heat flow path inside the smart-phone. To understand the heat flow path from CPU to screen through the interface material, heat dissipation mechanism was simulated and discussed.

Field-Controlled Electrical Switch with Liquid Metal.

When immersed in an electrolyte, droplets of Ga‐based liquid metal (LM) alloy can be manipulated in ways not possible with conventional electrocapillarity or electrowetting. This study demonstrates how LM electrochemistry can be exploited to coalesce and separate droplets under moderate voltages of ~1–10 V. This novel approach to droplet interaction can be explained with a theory that accounts for oxidation and reduction as well as fluidic instabilities. Based on simulations and experimental analysis, this study finds that droplet separation is governed by a unique limit‐point instability that arises from gradients in bipolar electrochemical reactions that lead to gradients in interfacial tension. The LM coalescence and separation are used to create a field‐programmable electrical switch. As with conventional relays or flip‐flop latch circuits, the system can transition between bistable (separated or coalesced) states, making it useful for memory storage, logic, and shape‐programmable circuitry using entirely liquids instead of solid‐state materials.

Soft Anisotropic Conductors as Electric Vias for Ga-Based Liquid Metal Circuits.

We introduce a method for sealing liquid metal (LM) circuits with soft anisotropic conductors that prevent leaking, while simultaneously allowing for electrical contact with skin and surface mounted electronics. These films are composed of polydimethylsiloxane (PDMS) embedded with vertically aligned columns of ferromagnetic Ag-Ni microparticles. The microparticles are magnetically aligned and support electrical conductivity only through the thickness (z-axis) of the elastomer film. Measurements on 10-40% (by wt) composites show moderate volumetric resistivity (as low as ρ = 0.03 Ω/m) through the thickness and no conductivity between adjacent traces. Functionality is demonstrated with several illustrative applications related to tactile sensing and electronics hardware integration.

Biomedical Implementation of Liquid Metal Ink as Drawable ECG Electrode and Skin Circuit

BackgroundConventional ways of making bio-electrodes are generally complicated, expensive and unconformable. Here we describe for the first time the method of applying Ga-based liquid metal ink as drawable electrocardiogram (ECG) electrodes. Such material owns unique merits in both liquid phase conformability and high electrical conductivity, which provides flexible ways for making electrical circuits on skin surface and a prospective substitution of conventional rigid printed circuit boards (PCBs).MethodsFundamental measurements of impedance and polarization voltage of the liquid metal ink were carried out to evaluate its basic electrical properties. Conceptual experiments were performed to draw the alloy as bio-electrodes to acquire ECG signals from both rabbit and human via a wireless module developed on the mobile phone. Further, a typical electrical circuit was drawn in the palm with the ink to demonstrate its potential of implementing more sophisticated skin circuits.ResultsWith an oxide concentration of 0.34%, the resistivity of the liquid metal ink was measured as 44.1 µΩ·cm with quite low reactance in the form of straight line. Its peak polarization voltage with the physiological saline was detected as −0.73 V. The quality of ECG wave detected from the liquid metal electrodes was found as good as that of conventional electrodes, from both rabbit and human experiments. In addition, the circuit drawn with the liquid metal ink in the palm also runs efficiently. When the loop was switched on, all the light emitting diodes (LEDs) were lit and emitted colorful lights.ConclusionsThe liquid metal ink promises unique printable electrical properties as both bio-electrodes and electrical wires. The implemented ECG measurement on biological surface and the successfully run skin circuit demonstrated the conformability and attachment of the liquid metal. The present method is expected to innovate future physiological measurement and biological circuit manufacturing technique in a large extent.