Room-temperature Liquid Metals Research Articles

Liquid metals enabled advanced cryobiology: development and perspectives

Cryosurgery and cryopreservation, as two important categories in cryobiology, have been impeded by the poor thermal conductivity of biological tissues or specimens. To improve this, diverse adjuvants, e.g., carbon-based materials, metallic nanoparticles, metallic oxide nanoparticles, etc ., have been exploited to improve the heat transfer in heat-targeted regions to increase the tumor elimination efficiency as well as the post-thaw viability of cryopreserved specimens. Nevertheless, these materials suffer poor thermal conductivities, controversial biosafety problems, and high expense. Gallium and its alloys, as a class of room-temperature liquid metals (LMs), have been widely studied in the past decade for their low melting point, minor toxicity, outstanding transformability, and conductivity. Integrated with these superior properties, they have been widely applied in multiple fields, such as thermal management, flexible electronics, and soft robotics. Recently, our laboratory has been devoted to fusing LMs with cryobiology and has made a series of progress. In this article, we will first briefly introduce preparation pathways to LM-based functional nanomaterials and composites. Then, how these materials realize improvement in biological heat transfer will be presented, followed by a discussion about the biosafety of these materials, which is an essential concern for the cryobiological field. Recent studies employing LMs in advanced cryosurgery and cryopreservation will also be highlighted. The present challenges and prospects of LMs towards further development in cryobiology will be put forward to point out the possible research direction.

Bismuth-based liquid metals: advances, applications, and prospects.

Bismuth-based liquid metals (LMs) are a large group of alloys with melting points slightly above room temperature. They are associated with fewer encapsulation constraints than room temperature LMs such as mercury, sodium-potassium alloys, and gallium-based alloys and are more likely to remain stable in the natural environment. In addition, their low melting point properties enable them to soften and melt via easy control. Bismuth-based alloys can also be modified with metal-based, carbon-based, and ceramic-based micro/nano particles as well as polymeric materials to create a series of novel composites owing to their outstanding functions. Based on these considerations, this review provides a comprehensive overview of bismuth-based LMs. The categories of bismuth and bismuth-based LMs are first briefly introduced to better systematize the physical and chemical properties of bismuth-based LMs. Based on these properties, bismuth-based LMs have been prepared using various methods, and this review briefly categorizes these preparation methods based on their finished forms (lumps, powders, and films). In addition, this review details the research progress of bismuth-based LMs in the fields of printed electronics, 3D printing, thermal management, biomedicine, chemical engineering, and deformable robotics. Finally, the challenges and future opportunities of bismuth-based LMs in the development process are discussed and visualized from different perspectives.

Room-Temperature Liquid Metals for Flexible Electronic Devices.

Room-temperature gallium-based liquid metals (RT-GaLMs) have garnered significant interest recently owing to their extraordinary combination of fluidity, conductivity, stretchability, self-healing performance, and biocompatibility. They are ideal materials for the manufacture of flexible electronics. By changing the composition and oxidation of RT-GaLMs, physicochemical characteristics of the liquid metal can be adjusted, especially the regulation of rheological, wetting, and adhesion properties. This review highlights the advancements in the liquid metals used in flexible electronics. Meanwhile related characteristics of RT-GaLMs and underlying principles governing their processing and applications for flexible electronics are elucidated. Finally, the diverse applications of RT-GaLMs in self-healing circuits, flexible sensors, energy harvesting devices, and epidermal electronics, are explored. Additionally, the challenges hindering the progress of RT-GaLMs are discussed, while proposing future research directions and potential applications in this emerging field. By presenting a concise and critical analysis, this paper contributes to the advancement of RT-GaLMs as an advanced material applicable for the new generation of flexible electronics.

Effect of electric field on the wetting behavior of GaInSnBiZn high-entropy alloy in NaOH aqueous solution

The GaInSnBiZn low-melting-point high-entropy alloy exhibits promising prospects for utilization in the realm of flexible electronic devices, offering a promising alternative to common binary or ternary room-temperature liquid metals. By utilizing the sessile drop method, the wetting behavior of GaInSnBiZn/SiO2 was investigated, focusing on the effects of applied voltage and NaOH solution concentration. It was revealed that the alloy's electro-wetting is primarily influenced by the generation and dissolution of the surface oxide layer, as well as the interaction of the electric double-layer effect. The optimal response voltages for achieving the fastest wetting rate were found to be 16 V, 10 V, 18 V, and 8 V in 0.5 mol/L, 1.0 mol/L, 1.5 mol/L, and 2.0 mol/L concentrations, respectively, with 18 V at 1.5 mol/L concentration identified as the optimal process selection. The spreading behavior of the alloy in low-concentration NaOH solutions followed Tanner's Law, while in the 2.0 mol/L concentration, significant repellence and wetting angle saturation were observed. The wetting process of the alloy at various stages was described using the power-law equation R = atc, while the wetting mechanism of the alloy was elucidated through the application of the Lippmann equation and the electric double-layer effect equation.

Minimizing interface thermal resistance via laser surface micropatterning for enhancing wetting of gallium-based liquid metal with copper

Thermal management systems are facing significant demand to dissipate increasing heat fluxes in time, however, heat transfer between solid surfaces is always obstructed due to the unperfect interfacial contact. Gallium-based room-temperature liquid metals (LM) are a type of emerging thermal interface materials (TIMs) with superior thermal conductivity and deformability, efficiently enhancing the through-interface thermal transfer. However, the poor wettability of LMs with engineering materials (e.g., copper), which leads to non-negligible remaining gap/air at the interfaces, limits the further reduction of thermal interface resistance. Herein, a laser micropatterning approach is presented to significantly improve LM wetting behaviors with copper surfaces in the assistance of HCl solution, with the thermal interface resistance minimized to ∼0.37 mm2·K/W which is four orders of magnitudes lower than that of two bare surfaces directly contacted and a quarter of that of bare surfaces with LM as TIM. Micropatterns featuring dense, shallow and open channels were designed and demonstrated to effectively expel trapped air while using a small amount of LM, which were both found necessary for reducing thermal interface resistance. We believe this study can lay a foundation for the further development and practical application of LMs based thermal management strategies.

Dry liquid metals stabilized by silica particles: Synthesis and application in photothermoelectric power generation

HypothesisGallium-based room-temperature liquid metals (LMs) have unique physicochemical properties; however, their high surface tension, low flowability, and high corrosiveness to other materials limit their advanced processing (including precise shaping) and application. Consequently, LM-rich free-flowing powders, named “dry LMs” that offer the inherent advantages of dry powders, should play a critical role in expanding the application scope of LMs. ExperimentsA general method of preparing silica-nanoparticle-stabilized LMs in the form of LM-rich powders (>95 wt% LM) is developed. FindingsDry LMs can be simply prepared by mixing LMs with silica nanoparticles in a planetary centrifugal mixer in the absence of solvents. As a sustainable dry-process route alternative to wet-process routes, this ecofriendly and simple method of dry LM fabrication has several advantages, e.g., high throughput, scalability, and low toxicity owing to the lack of organic dispersion agents and milling media. Moreover, the unique photothermal properties of dry LMs are used for photothermal electric power generation. Thus, dry LMs not only pave the way for the use of LMs in powder form but also provide a new opportunity for expanding their application scope in energy conversion systems.

Sonochemistry of Liquid-Metal Galinstan toward the Synthesis of Two-Dimensional and Multilayered Gallium-Based Metal-Oxide Photonic Semiconductors.

The scientific field of two-dimensional (2D) nanostructures has witnessed tremendous development during the last decade. To date, different synthesis approaches have been developed; therefore, various exceptional properties of this family of advanced materials have been discovered. It has recently been found that the natural surface oxide films of room-temperature liquid metals is an emerging platform for the synthesis of novel types of 2D nanostructures with numerous functional applications. However, most of the developed synthesis techniques for these materials are based on the direct mechanical exfoliation of 2D materials as research targets. This paper reports a facile and functional sonochemical-assisted approach for the synthesis of 2D hybrid and complex multilayered nanostructures with tunable characteristics. In this method, the intense interaction of acoustic waves with microfluidic gallium-based room-temperature liquid galinstan alloy provides the activation energy for synthesis of hybrid 2D nanostructures. The microstructural characterizations reveal the impact of sonochemical synthesis parameters, including the processing time and composition of the ionic synthesis environment, on the growth of GaxOy/Se 2D hybrid structures and InGaxOy/Se multilayered crystalline structures with tunable photonic characteristics. This technique shows promising potential for synthesis of various types of 2D and layered semiconductor nanostructures with tunable photonic characteristics.

Thermal and Electrical Properties of Liquid Metal Gallium During Phase Transition

Liquid metal gallium has been widely used in numerous fields, from nuclear engineering, catalysts, and energy storage to electronics owing to its remarkable thermal and electrical properties along with low viscosity and nontoxicity. Compared with high-temperature liquid metals, room-temperature liquid metals, such as gallium (Ga), are emerging as promising alternatives for fabricating advanced energy storage devices, such as phase change materials, by harvesting the advantageous properties of their liquid state maintained without external energy input. However, the thermal and electrical properties of liquid metals at the phase transition are rather poorly studied, limiting their practical applications. In this study, we reported on the physical properties of the solid–liquid phase transition of Ga using a custom-designed, solid–liquid electrical and thermal measurement system. We observed that the electrical conductivity of Ga progressively decreases with an increase in temperature. However, the Seebeck coefficient of Ga increases from 0.2 to 2.1 µV/K, and thermal conductivity from 7.6 to 33 W/(K∙m). These electrical and thermal properties of Ga at solid–liquid phase transition would be useful for practical applications.

Multiphase flow physics of room temperature liquid metals and its applications

Multiphase flow physics of room temperature liquid metals and its applications

Mechanical sintering-induced conductive flexible self-healing eGaInSn@PDA NDs/TPU composite based on structural design to against liquid metal leakage

Room-temperature liquid metals are potential candidates for developing flexible and reconfigurable conductive composites. However, an auxiliary sintering process is required to rupture the oxide and organically modified layers on the liquid metal (LM) nanodroplets (NDs) surface to reactivate their conductive and fluidic properties, thereby forming a continuous conductive pathway inside the composite. However, such a destructive strategy leads to leakage of liquid metal and destruction of composite integrity. Here, the “solvent volatilization strategy” was introduced to cause the organic solvent within thermoplastic polyurethane (TPU) to rapidly volatilize and be actively degassed during the polymerization process, forming densely packed micron-scale cavities. The polydopamine (PDA)-modified eGaInSn NDs were uniformly distributed and anchored to the inner wall of the cavity, providing sufficient filling space for the stress-ruptured eGaInSn@PDA NDs. During the application of mechanical pressure, the composite gradually converted from a dielectric state to a conductive state and it was able to quickly and repeatedly self-healing to restore conductivity after fracturing. In particular, no liquid metal pump-out or leakage was observed on the composite surface even after applying an 8 MPa high stress. In addition, the composite embedded with a high fraction eGaInSn@PDA NDs still exhibited high flexibility and had excellent electromagnetic shielding and X-ray attenuation capabilities.

Activated platinum in gallium-based room-temperature liquid metals for enhanced reduction reactions.

Room-temperature gallium-based liquid metals (LMs) have recently attracted significant attention worldwide for application in catalysis because of their unique combination of fluidic and catalytic properties. Platinum loading in LMs is expected to enhance the catalytic performance of various reaction systems. However, Pt-loaded methods for Ga-based LMs have not yet been sufficiently developed to improve the catalytic performance and Pt utilization efficiency. In this study, a novel method for the fabrication of Pt-incorporated LMs using Pt sputter deposition (Pt(dep)-LMs) was developed. The Pt(dep)-LMs contained well-dispersed Pt flakes with diameters of 0.89 ± 0.6 μm. The catalytic activity of the Pt(dep)-LM with a Pt loading of ∼0.7 wt% was investigated using model reactions such as methylene blue (MB) reduction and hydrogen production in an acidic aqueous solution. The Pt(dep)-LMs showed a higher MB reduction rate (three times) and hydrogen production (three times) than the LM loaded with conventional Pt black (∼0.7 wt%). In contrast to the Pt(dep)-LMs, solid-based Ga with a Pt loading of ∼0.7 wt% did not catalyze the reactions. These results demonstrate that Pt activation occurred in the Pt(dep)-LMs fabricated by Pt sputtering, and that the fluidic properties of the LMs enhanced the catalytic reduction reactions. Thus, these findings highlight the superior performance of the Pt deposition method and the advantages of using Pt-LM-based catalysts.

Liesegang Phenomenon of Liquid Metals on Au Film.

Room temperature liquid metals (LM) such as gallium (Ga) own the potential to react with specific materials which would incubate new application categories. Here, diverse self-organized ring patterns due to nonequilibrium reaction-diffusion and spreading-limitation of Ga-based LM clusters on gold (Au) film are reported, among which diffusion is the controlling step and the self-limiting oxide layer plays the role of kinetic barrier. Such phenomena, classically known as the Liesegang rings, mainly occur in electrolyte media. Unlike existing systems, the present periodic crystallization mechanism enables highly symmetric spatiotemporal periodic Liesegang rings on a smaller scale under ambient conditions. Typically, the Ga-Au and eutectic gallium-indium alloy (EGaIn)-Au reaction-diffusion-spreading systems are constructed, obtaining the revert type and hybrid type concentric Liesegang patterns, respectively. The competitive patterning behavior of the intermediate phase products AuGa2 and AuIn2 in hybrid Liesegang patterns is further analyzed by altering the initial Ga/In mass ratio, first-principles calculations, and molecular dynamic simulations. When the mass ratio of In in GaIn alloy exceeds 15%, it will preferentially react with Au. The discovery of LM Liesegang phenomenon is expected to be a flashpoint for self-organized reaction-diffusion systems and offers promising rules for diverse areas such as materials synthesis and the jewelry design industry.

Toxicity and Biocompatibility of Liquid Metals.

Recently, room-temperature liquid metals have attracted increasing attention from researchers owing to their excellent material properties. Systematic interpretation of the potential toxicity issues involved is essential for a wide range of applications, especially in the biomedical and healthcare fields. However, even with the exponential growth of related studies, investigation of the toxicological impact and possible hazards of liquid metals to organisms is still in its infancy. This review aims to provide a comprehensive summary of the current frontier of knowledge on liquid metal toxicology and biocompatibility in different environments. Based on recent studies, this review focuses on Ga and Bi-based in different states. It is necessary to evaluate their toxicity considering the rapid increase in research and utilization of such liquid metal composites. Finally, existing challenges are discussed and suggestions are provided for further investigation of liquid metal toxicology to clarify the toxicological mechanisms and strategies are provided to avoid adverse effects. In addition to resolving the doubts of public concern about the toxicity of liquid metals, this review is expected to promote the healthy and sustainable development of liquid metal-based materials and their use in diverse areas, especially those related to health care.

A low melting high entropy alloy with conformal electroconductivity for flexible electronic circuits

The multi-phase equiatomic GaInSnZn high entropy alloy (HEA) has been synthesized via induction-melting, which exhibits similar behavior as compared to remaining room-temperature liquid metals (LMAs). This HEA, as well known as a low melting HEA, is a near-eutectic alloy with melting point around 9.08 ℃ extracted from DSC results and electrical conductivity about 4.68 MS/m at 20 ℃. The phase constituents are corroborated by theoretical calculations of the formation criteria regarding HEAs. The feasibility as a promising direct-writing inks of the flexible electronic circuits to replace several LMAs is demonstrated by a sequence of conceptual experiments and contact angle measurements. A trade-off among melting temperature, conductivity and costs superior to conventional LMAs is considered to origin from the multi-principal component concepts. This study sheds lights on the fabrication of flexible electronic circuits at low costs and may open novel insights for developing low melting point HEAs.

Liquid-metal micro-networks with strain-induced conductivity for soft electronics and robotic skin

Thin-film devices made of room-temperature liquid metals (LMs) have contributed to the development of electronic skin for human-robot/machine interfaces but still have limitations, including degradations of performance and robustness under repeated deformations. In this paper, we describe an interesting phenomenon of the formation of LM microscale networks (LMMNs) and propose to use the LMMNs for fabricating thin-film conductors. A simple layer-by-layer (LBL) deposition process enables the growth of a hierarchical structure of LM microdroplets that forms a conductive network (i.e., LMMN) when stretched. The strain-history behavior of LMMNs allows conductivity enhancement up to 2.37 × 106 S m−1 in response to increased tensile strains. By adjusting the number of LM layers in LBL deposition, the gauge factor (0.2 ≤ GF ≤ 1), the linearity, and the sheet resistance of LMMN films can be easily controlled, providing high potentials in various applications, including skin-mountable circuits, energy harvesters, and soft artificial skin.

Accurate and Efficient Calculation of the Solution Enthalpy and Diffusivity of Solutes in Liquid Metals Using Machine Learning Potential.

Liquid metals (LMs) have various applications in energy systems, such as coolants in advanced nuclear reactors. In addition, room-temperature LMs are attracting attention as flexible components in robotics and electronics and as novel chemical reaction media to form low-dimensional materials. In many of these applications, the capabilities of LMs can be further enhanced if one can better understand and control the chemical reactivity of LMs, which is largely affected by the stability and mobility of solutes in LMs. Here, we propose an automated method using a machine learning moment tensor potential to efficiently calculate the solution enthalpy and diffusivity of solutes in LMs. From several test cases in liquid Na, we demonstrate that the method can achieve an accuracy comparable to that of a direct calculation using first-principles molecular dynamics, while significantly reducing the calculation cost to the order of 1/10 to 1/100. The method is expected to contribute to the advancement of LM chemistry and the development of new LMs.

A Short History of Fusible Metals and Alloys – Towards Room Temperature Liquid Metals

AbstractLiquid metals are a class of materials with a millennia‐long history, albeit until 200 years ago, mostly centered on mercury‐based applications. The knowledge of mercury's toxicity and the discovery of it's bioaccumulation and biomagnification in the late 20th century resulted in phasing out mercury for copious application. Lead‐based, bismuth‐based, and sodium‐based technology has partially replaced mercury, but due to toxicity or reactivity issues, replacements for lead and sodium are sought. The discovery of indium and, especially, gallium has allowed for the third generation of alloys with a melting point close to room temperature. This review gives a comprehensive overview of the technological developments of fusible and liquid metals, i. e., metals and alloys with melting points below ca. 250 °C, from the early days to current research and industrial application. Special emphasis is focused on important steppingstones and recent developments of gallium‐based alloys as well as how they could be used for future applications.

Formation of Multiphase Soft Metal from Compositing GaInSn and BiInSn Alloy Systems

Emerging functional room-temperature liquid metals generally include gallium-based and bismuth-based alloys. Their excellent electrical conductivity, thermal conductivity, flexibility, fluidity, and reflectivity can enable their application in many fields. However, there are quite a few problems that need to be solved before their application. For example, liquid metals are often difficult to adhere and diffuse on solid substrates due to their high surface tension and fluidity, which hinders the application and promotion. Herein, we report a method to develop multiphase soft metals from gallium- and bismuth-based alloys. Particularly, room-temperature multiphase soft metals of GaBiInSn alloys developed from Ga67In20.5Sn12.5 and Bi33.1In51.3Sn15.6 alloys via compositing, mixing, and heating treatment are first reported, which include the solid phase, liquid phase, and paste phase, respectively. The free metal alloy grains are dispersed in GaBiInSn alloys and transition constantly among different phases. More importantly, the structure, size, density, and other characteristics of free metal alloy grains can be modified by adjusting the mass ratio of each component. The surface morphology, structure, wettability, adhesion, work function, and photoelectric characteristics of multiphase soft metals can be controlled and optimized by controlling phase transition. As a result, the wettability of the obtained Ga50.25Bi8.28In28.2Sn13.27 is obviously improved (the contact angle decreased from 118.5° to 94°), with a high work function (4.75 eV), high reflectivity (78.14%), low electrical resistivity (2.94 × 10–7 Ω m). Meanwhile, several typical applications of the multiphase materials were demonstrated. The results of this work will offer a promising strategy to directly prepare liquid metal flexible electrodes on PI, PET, and silk, and also, the stability can be kept well under large deformation and curling conditions.

Gallium-Indium-Tin Eutectic as a Self-Healing Room-Temperature Liquid Metal Anode for High-Capacity Lithium-Ion Batteries.

Owing to their intrinsic properties, such as deformability, high electrical conductivity, and superior electrochemical performance, room-temperature liquid metals and liquid metal alloys have attracted the attention of researchers for a wide variety of applications, including portable and large-scale energy storage applications. In this study, novel gallium-indium-tin eutectic (EGaInSn) room-temperature liquid metal nanoparticles synthesized using a facile and scalable probe-ultrasonication method were used as anode material in lithium-ion batteries. The morphology, geometry, and self-healing properties of the synthesized room-temperature liquid metal nanoparticles were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (SEM/EDS and TEM/EDS). The synthesized room-temperature liquid metal nanoparticles delivered a specific capacity of 474 mAh g–1 and retained 77% of the stable reversible capacity after 500 galvanostatic charge-discharge cycles at a constant current density of 0.1 A g–1. The high theoretical specific capacity, combined with its self-healing and fluidic features, make EGaInSn room-temperature liquid metal nanoparticles a potential anode material for large-scale energy storage applications.

Liquid Metal-Derived Two-Dimensional Layered Double Oxide Nanoplatelet-Based Coatings for Electromagnetic Wave Absorption

Room-temperature liquid metals offer intriguing chemistry for obtaining atomic nanomaterials with unique composition and morphologies. However, the use of liquid metals for the synthesis of layered double oxide (LDO) materials has rarely been reported. When surrounded with water, liquid metal alloys produce low-dimensional hydroxides on their interfacial regions. In this work, highly electrostatically polarized two-dimensional (2D) aluminum hydroxides, featuring OH bonds, are devised as adsorption sites for divalent cations including Ni2+, Co2+, Mg2+, Mn2+, Zn2+, and Fe2+ ions. For Ni2+ and Co2+ ions, remarkably, through changing synthesis conditions, different orientations of 2D Al/NiCo-LDO nanoplatelets can be synthesized. The change in the orientation of the surface platelets, that is, parallel or vertical, to the plane of aluminum oxide resulted in excellent electromagnetic wave (EW) absorption performance. The effective absorption bandwidth reaches 5.61 GHz at a composite thickness of only 1.7 mm. The different nanomorphology and annealing temperature of Al/NiCo-LDO resulted in fundamentally different electromagnetic losses. Results indicating the developed framework have tunable and excellent EW absorption capabilities. 2D Al/NiCo-LDOs prepared by the developed liquid metal synthesis method shows a great promise for applications in the fields of EW absorption and electromagnetic protection. Due to their lightweight, high-surface-area, and mechanically strong material features, aluminum oxide compounds are suitable for the synthesis of other LDO compounds including Mg2+, Mn2+, Zn2+, and Fe2+. The incorporation of a variety of divalent cations into the nanostructure and facet engineering are promising pathways for the production of reinforced lightweight nanomaterials for utilization in various applications. This work fundamentally explores the effect of achieved materials' polarization through fully characterizing the absorption.