Room Temperature Liquid Metal Research Articles

Rheology of liquid metal particle-based polymer composites: A comparative study

Using room-temperature liquid metal particles as fillers in polymer composites (PCs) has recently been of utmost interest as the resultant composites exhibit improved toughness along with electrical and thermal conductivity. This paper presents a comprehensive study on shear and extensional rheology of the aqueous solutions (inks) of liquid EGaIn (eutectic gallium-indium) particle and poly(ethylene oxide)-based PCs. The rheology of this material system is compared to solid-state, rigid graphene-based PC inks having the same polymer matrix and filler concentrations. Results show that EGaIn-based PC inks exhibit unique rheological behavior that is inconsistent with that of the conventional rigid filler-based Polymer Nanocomposites (PNs), exemplified by increased extensional flow capability and elasticity. We postulate that the source of this behavior is the elastic nature of the oxide covered EGaIn particles. EGaIn-based PCs eliminate common trade-offs for conductive PCs and thus can have a significant impact in several technologies including solid-state energy storage and 3D-printing.

Water-Induced Breaking of the Coulombic Ordering in a Room-Temperature Ionic Liquid Metal Complex.

Control of ion arrangements in ionic liquids represents a major challenge owing to the presence of the predominant coulombic interactions between cationic and anionic ion species that forms the coulombic ordering. Here, water-induced ion rearrangement in a room-temperature ionic liquid (RT-IL) metal complex, (1-ethyl-3-methylimidazolium)2 [MnN(CN)4 ], is demonstrated through coordinative interactions between anions. Solidification occurred, which was associated with the formation of a "separated" structure consisting of cation columns and anionic cyanide-bridged one-dimensional coordination polymers. The energy diagram is in accord with the resultant RT-IL incorporating mononuclear [MnN(CN)4 ]2- molecules being a kinetic phase stabilized by inter-ion repulsions of the anionic divalent metal complex moieties. Water acts to decrease the coulombic interactions, including repulsion, giving rise to breaking of the coulombic ordering arising from coordination bond formation in the IL phase.

Phase Separation in Liquid Metal Nanoparticles

Nanoparticles produced from gallium-based liquid metal alloys have been explored for developing applications in the fields of electronics, catalysis, and biomedicine. Nonetheless, physical properties, such as phase behavior at micro-/nanosize scale, are still significantly underexplored for such nanoparticles. Here, we conduct an in situ investigation of phase behavior for gallium-based liquid metal nanoparticles and discover the unprecedented coexistence of solid particles in spherical liquid metal shells without the support of a crystalline substrate. The particles can also transform into solid Janus nanoparticles after temperature cycling. In addition, we investigate the optical properties of the nanoparticles before and after phase separation using in situ electron energy-loss spectroscopy. Most importantly, we discover that increasing the content of indium within the nanoparticle can stabilize the solid-core/liquid-shell structure at room temperature. This study provides a foundation to engineer liquid metal nanoparticles for developing new applications in nanoscale optical platforms and shape-configurable transformers.Although various electronic, chemical, and biomedical applications have been demonstrated for nanoparticles made from gallium-based liquid metal alloys, fundamental physical properties such as phase behavior of such nanoparticles are still significantly underexplored. Here, Tang and coworkers present the in situ investigation of phase separation in binary and ternary spherical liquid metal nanoparticles upon cooling, and demonstrate the coexistence of solid core/liquid shell without the support of a crystalline substrate. This study provides insight into engineering such nanoparticles for the development of new applications.Despite gallium-based liquid metal alloys attracting extensive attention for various applications, their phase behavior at the nanoscale is still underexplored. Understanding the impact of phase separation in nanoparticles can be extremely useful for developing new structures and exploring suitable applications. Here, we report on the investigation of phase behavior for spherical nanoparticles made from gallium-based liquid metal alloys upon cooling. We discover the thermally stable coexistence of solid cores in spherical liquid metal shells without the support of a crystalline substrate at room temperature. Given the unique properties of liquid metal, together with the facile process for producing core-shell and Janus nanoparticles, this work will encourage further investigation of the properties of such nanoparticles for developing applications in the fields of electronics, catalysis, nanomedicine, and beyond.

Microchannel Structural Design For a Room-Temperature Liquid Metal Based Super-stretchable Sensor

Room-temperature liquid metal has been widely used in flexible and stretchable sensors, focusing on embedding liquid metal in microchannels, liquid metal microdroplets formation, captive sensors, and liquid metal nanoparticles, etc. In this paper, a facile Eutectic Galium-Indium (EGaln) liquid-based microfluidic high-sensitivity, skin-mountable, and ultra-soft stretchable sensor is developed. It comprises Ecoflex microfluidic assembly filled with EGaln, which serves as the working fluid of the stretchable sensor. The lithography method is applied to achieve microfluidic channel. The microfluidic channel is optimized by using topology method and finite element analysis, making this device with high conformability and high stretchability. This method achieved an outstanding effect on elastomer-encapsulated strain gauge, which displays an approximately linear behavior with a gauge factor (GF). The GF could reach as high as 4.95 when the strain ultimately reached 550%. Applications of detection of the joints, fingers, and wrists has been conducted and showed excellent results. This work can further facilitate the exploration and potential realization of a functional liquid-state device technology with superior mechanical flexibility and conformability.

A liquid metal robot driven by hybrid-fluid

Since the 20th century, robots have been widely used in many fields such as manufacturing and life services. Traditional rigid robots are limited by degrees of freedom and are difficult to adapt to the dynamic and unstructured complex environment. Soft robots have attracted wide attention in recent years due to their flexibility and adaptability to the surroundings. Room temperature liquid metal combines the perfect properties of liquid and metal, such as excellent thermal conductivity, electrical conductivity, fluidity and low toxicity etc. Meanwhile, liquid metal is identified to be very useful in robotics due to its inherent flexibility. At present, the liquid metal can mainly be driven by electrical field, magnetic field and chemical reaction, all of which need to be carried out in solution environments. From an alternative, a rolling robot is proposed based on gallium-based liquid metal driven by hybrid-fluid. The movement of the liquid metal in the spiral tube alters the center of gravity of the device, pushing the entire robotic system to achieve its rolling locomotion, which frees the motion of liquid metal from the solution environment where its locomotion generally relies on. Besides, the hybrid-fluid driving can be achieved by thermal driving and chemical reaction, respectively. In the present research, the principles of two different hybrid-fluid driving mechanisms were interpreted. Prototyping devices were designed, and a series of conceptual experiments were conducted to clarify the factors affecting the motion of the device, which demonstrate the feasibility and prospects of hybrid-fluid driving robot. The present results are expected to be valuable for developing future of soft robotics technologies.

Development of a High Flow Rate 3-D Electroosmotic Flow Pump.

A low voltage 3D parallel electroosmotic flow (EOF) pump composed of two electrode layers and a fluid layer is proposed in this work. The fluid layer contains twenty parallel fluid channels and is set at the middle of the two electrode layers. The distance between fluid and electrode channels was controlled to be under 45 μm, to reduce the driving voltage. Room temperature liquid metal was directly injected into the electrode channels by syringe to form non-contact electrodes. Deionized (DI) water with fluorescent particles was used to test the pumping performance of this EOF pump. According to the experimental results, a flow rate of 5.69 nL/min was reached at a driving voltage of 2 V. The size of this pump is small, and it shows a great potential for implanted applications. This structure could be easily expanded for more parallel fluid channels and larger flow rate.

Magnetically‐ and Electrically‐Controllable Functional Liquid Metal Droplets

AbstractGallium‐based room temperature liquid metal alloys have recently been explored to be an emerging functional material. They have attracted particular attentions in a variety of applications due to their unique properties. Many of the applications are based on the precise control over the motion of liquid metal, and yet, the fact that currently lacking the advanced and reliable controlling methods greatly hinders the potential of liquid metal to be applied in a wider range of fields. In this study, an innovative approach is developed to obtain functional liquid metal (FLM) by modifying it with copper–iron magnetic nanoparticles (Cu–Fe NPs). The magnetic modification process enables the Cu–Fe NPs to be suspended within the liquid metal and form the FLM. The FLM exhibits similar appearance, actuating behaviors, and deformability in alkaline solutions to those of pure liquid metal alloys. Meanwhile, the magnetic modification enables the precise and rapid manipulation of the liquid metal using a magnetic field. Most importantly, for the first time, the precise control and climbing locomotion of the FLM is demonstrated with the interworking of both electric and magnetic fields simultaneously. The remarkable features of the FLM may represent vast potentials toward the development of future intelligent soft robots.

Chemically modifying the mechanical properties of core-shell liquid metal nanoparticles.

Eutectic gallium-indium (EGaIn) is a room temperature liquid metal that can be readily fabricated into nanoparticles which naturally form a thin, passivating gallium oxide shell. These core-shell nanoparticles are of interest for a variety of stimuli-responsive applications, which often utilize physical deformation of the particles to release the molten, conductive payload from within the gallium oxide shell. In the present work, we introduce a variety of chemical strategies to produce EGaIn nanoparticles which exhibit a wide range of gallium oxide shell thicknesses. These chemically modified oxide thicknesses are then correlated to the core-shell liquid nanoparticles' mechanical properties by subjecting the particles to orthogonal characterization techniques; XPS for measurement of the gallium oxide shell thickness and nanoindentation for measurement of particle stiffness and elastic modulus. Additionally, nanoindentation is used to determine the onset of particle rupture and resultant conductivity. Ultimately, quantification of the relationships between chemical treatment and derivative mechanical properties in liquid metal nanoparticles will enable advanced applications of these colloids, such as in tailored self-healing and responsive electronic devices.

Room-temperature liquid metal and alloy systems for energy storage applications

Liquid metals and alloy systems that feature inherent deformability, high electronic conductivity, and superior electrochemical properties have enabled further development of next-generation energy storage devices.

Planar, Multifunctional 3D Printed Antennas Using Liquid Metal Parasitics

This paper describes a liquid metal-based multifunctional antenna capable of wideband frequency tuning, dual band operation, and polarization reconfiguration. The radiating elements consist of parasitically-excited plugs of room-temperature liquid metal in 3D printed channels. Syringe pumps flow the gallium-alloy plugs in proximity to a capacitive feeding structure. This non-contact feeding scheme separates the metal flow path from the SMA connector and lends mechanical robustness at the feed while allowing impedance matching over a wide range of frequencies. Sliding the plug along a right-angle bend enables linear polarization reconfiguration, while simultaneously placing plugs in both orthogonal channels can generate circular or 45° linear polarization. Dual band operation is also supported by infusing plugs of two dissimilar lengths into the two channels. Simulation and measurement results demonstrate that this antenna can tune its impedance over a decade (10:1 frequency range) maintaining a 2:1 VSWR and achieve a polarization diversity >12 dB. The pumped plugs can circulate at a peak velocity of 50 mm/s, currently limited only by our pumping equipment. Repeatability analysis is also performed by cycling the plug actuation more than 1100 times. More complex designs can exploit this design concept to develop new types of highly versatile, multi-functional antennas.

Creating 3D printed magnetic devices with ferrofluids and liquid metals

Combining electrical and magnetic materials in the same part has been a challenge in 3D printing due to difficulties co-printing complex materials in many additive manufacturing processes. Past 3D printed inductors and other similar magnetic devices have therefore either lacked the magnetic materials necessary for improved performance, or required sintering at high temperatures for extended periods, beyond the capability of most 3D printable polymers. In this work, we demonstrate a room temperature process for incorporating conductive and magnetic materials into the same 3D printed device. A multi-stage fabrication process based on 3D printing followed by fill with magnetic and conductive fluids is proposed. Multi-layer microfluidic channels for magnetic passives are first printed in a stereolithography process. The microfluidic systems are then filled with room temperature liquid metal, a gallium alloy liquid at room temperature, and ferrofluid to create inductors, transformers and wireless power coils. Through the addition of ferrofluid as a magnetic material, increases in inductance density by nearly a factor of three were demonstrated, in addition to coupling improvements for transformer and wireless power coils compared to the devices before magnetic fill.

Direct measurements of laser absorptivity during metal melt pool formation associated with powder bed fusion additive manufacturing processes

Direct calorimetric measurements are used to study the effective optical absorptivity at 1070 nm laser wavelength for bulk and powder-coated discs of industrially relevant metals. Effective absorptivity is plotted as a function of nominal laser power from 30 up to 600 W for scanning velocities of 100, 500, and 1500 mm/s. The absorptivity versus power curves of the bulk materials typically shows a reduction in effective absorptivity until the beginning of the formation of a keyhole-type surface depression that is associated with an increased absorption of the laser light in the growing keyhole until a saturation value is reached. For powders, an additional plateau of higher absorptivity can be observed for low laser power, until the curves qualitatively collapse when full melting of the powder tracks is achieved. It is shown that, under conditions associated with laser powder-bed fusion additive manufacturing, absorptivity values can vary greatly, and differ from both room temperature powder layer measurements and liquid metal estimates from the literature.

Galinstan liquid metal breakup and droplet formation in a shock-induced cross-flow

Liquid metal breakup processes are important for understanding a variety of physical phenomena including metal powder formation, thermal spray coatings, fragmentation in explosive detonations and metalized propellant combustion. Since the breakup behaviors of liquid metals are not well studied, we experimentally investigate the roles of higher density and fast elastic surface oxide formation on breakup morphology and droplet characteristics. This work compares the column breakup of water with Galinstan, a room-temperature eutectic liquid metal alloy of gallium, indium and tin. A shock tube is used to generate a step change in convective velocity and back-lit imaging is used to classify morphologies for Weber numbers up to 250. Digital in-line holography (DIH) is then used to quantitatively capture droplet size, velocity and three-dimensional position information. Differences in geometry between canonical spherical drops and the liquid columns utilized in this paper are likely responsible for observations of earlier transition Weber numbers and uni-modal droplet volume distributions. Scaling laws indicate that Galinstan and water share similar droplet size-velocity trends and root-normal volume probability distributions. However, measurements indicate that Galinstan breakup occurs earlier in non-dimensional time and produces more non-spherical droplets due to fast oxide formation.

High-Voltage, Room-Temperature Liquid Metal Flow Battery Enabled by Na-K|K-β″-Alumina Stability

Summary Flow batteries are a compelling grid-scale energy storage technology because the stored energy is decoupled from the system power. Aqueous redox flow batteries (RFBs), however, are limited by low open-circuit voltages (OCVs). Replacing the aqueous negative electrolyte (negolyte) with liquid alkali metals—of which Na-K, a room-temperature liquid metal alloy, is attractive—would increase the OCV considerably. However, a suitable solid electrolyte has not been reported for Na-K. Here we show that K-β″-alumina is a selective and robust K+ ion conductor in contact with Na-K, to which it is stable with minimal exchange of Na. We report the cycling of cells with OCVs of 3.1–3.4 V employing aqueous and nonaqueous positive electrolytes (posolytes), and power density tests showing promising maximum power densities of 65 mW cm−2 at 22°C and >100 mW cm−2 at 57°C, ohmically limited by 330-μm K-β″-alumina membranes. Further development of Na-K|K-β″-alumina batteries could unlock cost-effective energy storage.

Self-Healing Liquid Metal and Si Composite as a High-Performance Anode for Lithium-Ion Batteries

Si is among the highest theoretical capacity anodes for lithium-ion batteries, but it suffers from huge volume expansion during lithiation. Here we report a new approach to alleviating the volume change-induced degradation of Si anodes by mixing Si with a room-temperature liquid metal (LM), namely, Ga–Sn alloy. The Ga–Sn alloy is fluid with self-healing ability, acting as the liquid buffer for the Si upon lithiation and delithiation and healing the cracks caused by the volume expansion and contraction. The resulting Si/LM composite exhibits a high capacity and excellent cyclicability. The composite anode delivers a reversible capacity of ∼670 mAh/g after 1000 cycles, with an outstanding rate capability.

Control of Gallium Oxide Growth on Liquid Metal Eutectic Gallium/Indium Nanoparticles via Thiolation.

Eutectic gallium-indium alloy (EGaIn, a room-temperature liquid metal) nanoparticles are of interest for their unique potential uses in self-healing and flexible electronic devices. One reason for their interest is due to a passivating oxide skin that develops spontaneously on exposure to ambient atmosphere which resists deformation and rupture of the resultant liquid particles. It is then of interest to develop methods for control of this oxide growth process. It is hypothesized here that functionalization of EGaIn nanoparticles with thiolated molecules could moderate oxide growth based on insights from the Cabrera-Mott oxidation model. To test this, the oxidation dynamics of several thiolated nanoparticle systems were tracked over time with X-ray photoelectron spectroscopy. These results demonstrate the ability to suppress gallium oxide growth by up to 30%. The oxide progressively matures over a 28 day period, terminating in different final thicknesses as a function of thiol selection. These results indicate not only that thiols moderate gallium oxide growth via competition with oxygen for surface sites but also that different thiols alter the thermodynamics of oxide growth through modification of the EGaIn work function.

Liquid metal as novel lubricant in a wide temperature range from −10 to 800 °C

Microscopic contacts commonly exist on the surfaces when applying loads between the frictional pairs. Under harsh environments, such as extremely high temperature and load, sliding devices will encounter devastating wear loss, eventually leading to the materials failure. Traditional liquid lubricants could only work in a narrow temperature range due to their poor thermal stabilities. A kind of room temperature liquid metal (LM), Ga68.5In21.5Sn10, could be used in an ultra-wide range of temperatures. In this work, the tribological properties of LM has been investigated for Si3N4/steel contact at three temperatures (−10, 20 and 800 °C), which was the first research in such wide range of temperature for liquid lubricants. Results indicate that LM exhibited excellent tribological performances. Surface analyses suggest that the predominant properties at −10 and 20 °C were ascribed to the tribofilms composed of metal oxides, such as Fe2O3, Ga2O3, In2O3, and SnO2. The main product intermetallic compound FeGa3 contributed to forming the boundary lubrication film at 800 °C.

Gas eruption phenomenon happening from Ga-In alloy in NaOH electrolyte

We report a gas eruption phenomenon caused by electrolysis of a liquid Ga-In alloy in an electrolyte, especially NaOH solution. A volcanic eruption-like blowout of gas occurred from the orifice on the alloy surface. In addition to the gas plume, large gas bubbles were also generated and the total gas yield increased as the In ratio was increased. It is found that the destructiveness of the passivation layer on the Ga-In alloy is critical to gas generation. The mechanism of gas eruption can be ascribed to a galvanic interaction between the passivation film and the connected alloy, because of their different electrochemical activity in the electrolyte. Further investigation demonstrated that the lattice of the film expands because of the incorporation of indium, which brings about the decrease in the bandgap and finally enhances more gas generation. These findings regain the basic understanding of a room temperature liquid metal inside an electrolyte.

Sonication‐Assisted Synthesis of Gallium Oxide Suspensions Featuring Trap State Absorption: Test of Photochemistry

AbstractGallium is a near room temperature liquid metal with extraordinary properties that partly originate from the self‐limiting oxide layer formed on its surface. Taking advantage of the surface gallium oxide (Ga2O3), this work introduces a novel technique to synthesize gallium oxide nanoflakes at high yield by harvesting the self‐limiting native surface oxide of gallium. The synthesis process follows a facile two‐step method comprising liquid gallium metal sonication in DI water and subsequent annealing. In order to explore the functionalities of the product, the obtained hexagonal α‐Ga2O3 nanoflakes are used as a photocatalytic material to decompose organic model dyes. Excellent photocatalytic activity is observed under solar light irradiation. To elucidate the origin of these enhanced catalytic properties, the electronic band structure of the synthesized α‐Ga2O3 is carefully assessed. Consequently, this excellent photocatalytic performance is associated with an energy bandgap reduction, due to the presence of trap states, which are located at ≈1.65 eV under the conduction band minimum. This work presents a novel route for synthesizing oxide nanostructures that can be extended to other low melting temperature metals and their alloys, with great prospects for scaling up and high yield synthesis.

Paper‐based capillary action

Researchers in the US present integration of paper-based microfluidics with liquid metal as a method for liquid metal transport through capillary action. Capillary action transport moves liquid by using the intermolecular forces between the liquid and a solid. If you take a material, such as a polymer, that contains different sized microfluidic channels, a specific channel can be selected for fluid transport if that channel is actuated. Actuation of fluidic channels is used in a variety of applications where signals need to be blocked and activated at different times. These include circuit switches, filters and various applications within antennas. Typically, liquid metal is moved by mechanical (e.g. syringes or pumps), or electrochemical (e.g. applied voltage) methods. In this issue of Electronics Letters, Matthew Moorefield and colleagues at the University of Hawaíi at Mānoa, report the first use of paper actuation to transport liquid metal using hydrophobic filter paper. Compared to mechanical and electrochemical methods, the method removes the need for an external power supply, providing a sustainable and unique alternative for liquid metal transport. “A potential application for this transportation method is a planar circuit that would be hampered by an electrical actuation network, or that doesn't have enough power or room in the device for a mechanical pump,” said Moorefield. Moorefield and colleagues have been working with the liquid metal Galinstan - a dense eutectic alloy of gallium, tin and indium - since 2011. The idea to use paper-based microfluidics to reconfigure a circuit grew out of a problem that the authors had when using syringes to remove a carrier fluid from around liquid metal. They had to use specialised geometries in microfluidic channels to position the liquid metal, and relied on its high surface tension to keep it in place. However, using the syringe was creating more force than was needed. A paper towel was then used to remove the carrier fluid as an attempt to reduce the required actuation force of the liquid metal. These experiments revealed that paper-based actuation was possible and became a natural development step for the authors. Moorefield and colleagues tested the initial idea with various grades of filter paper. “The change to filter paper in place of commercial paper towel was the most challenging part of the process” explains Moorefield. After optimising the experimental conditions required for paper-based liquid metal transport, the authors began designing a functional device. In their Letter the team present a simple switch device, designed to have a wide operating bandwidth. The switch is based on a 2.4 mm-wide copper microstrip, which has a 20 mm gap cut into its structure to create the non-operational OFF state. The size of the gap in the microstrip was calculated to give the switch a wide operating frequency range of between 50 MHz and 10 GHz. Liquid metal is transported between a reservoir and main channel, once the channel is actuated by placing the paper at the outlet of the main channel. Capillary forces then pull the liquid metal through a polymer placed within the gap of the microstrip into the main channel, and the device is switched onto the ON state with measurable microwave frequency transmission. Two members of the liquid-metal research team conducting research at the University of Hawaíi at Mānoa. Microstrip series switch used to demonstrate paper-based capillary actuation. The switch is fabricated by creating a physical break in the copper of a microstrip transmission line and placing a microfluidic channel over the break. When filled with Galinstan liquid metal and an electrolyte, paper-based capillary action is used to reposition the liquid metal turning the switch on. The choice of liquid metal being transported is limited by the operational environment. Galistan is a popular choice for room temperature liquid metal transport owing to its high viscosity and low toxicity properties. Eutectic-gallium-indium is also used in the research environment, and mercury is still used in some applications. The work reported in this Letter has the potential to expand the use of liquid metal for electronic circuits and other applications, by providing a simple and robust method for liquid metal actuation. Moorefield's research group is focused on adapting the controlled motion of liquid metal in microwave devices and are continuing their work on reconfigurable adaptive antennas. Moorefield explained that they “expect the use of liquid metals in reconfigurable devices to become more common in the next decade, and these devices may become commercialised products as the actuation and integration techniques mature”.