Liquid Metal Research Articles

3D Soft Architectures for Stretchable Thermoelectric Wearables with Electrical Self-Healing and Damage Tolerance.

Flexible thermoelectric devices (TEDs) exhibit adaptability to curved surfaces, holding significant potential for small-scale power generation and thermal management. However, they often compromise stretchability, energy conversion, or robustness, thus limiting their applications. Here, the implementation of 3D soft architectures, multifunctional composites, self-healing liquid metal conductors, and rigid semiconductors is introduced to overcome these challenges. These TEDs are extremely stretchable, functioning at strain levels as high as 230%. Their unique design, verified through multiphysics simulations, results in a considerably high power density of 115.4µWcm⁻2 at a low-temperature gradient of 10°C. This is achieved through 3D printing multifunctional elastomers and examining the effects of three distinct thermal insulation infill ratios (0%, 12%, and 100%) on thermoelectric energy conversion and structural integrity. The engineered structure is lighter and effectively maintains the temperature gradient across the thermoelectric semiconductors, thereby resulting in higher output voltage and improved heating and cooling performance. Furthermore, these thermoelectric generators show remarkable damage tolerance, remaining fully functional even after multiple punctures and 2000 stretching cycles at 50% strain. When integrated with a 3D-printed heatsink, they can power wearable sensors, charge batteries, and illuminate LEDs by scavenging body heat at room temperature, demonstrating their application as self-sustainable electronics.

MHD flows through ferromagnetic rectangular ducts in liquid metal blankets

MHD flows through ferromagnetic rectangular ducts in liquid metal blankets

Steady and transient analysis on thermal hydraulic characteristic of helical coiled once-through steam generator of liquid metal fast reactor

A transient model for thermal–hydraulic characteristics of helical coiled once-through steam generator (HCOTSG) of liquid metal fast reactor was established based on global discrete grid method. The model meshed the liquid metal circuit and water-steam circuit. Meanwhile, unsteady heat conduction equations were built to accurately simulate coupled heat transfer between two sides. Four-equation drift-flux method was adopt for water-steam flow. Taking lead–bismuth fast reactor as example, thermal–hydraulic characteristics of HCOTSG were first calculated under steady conditions. It was found that heat flux distribution along steam generator is extremely uneven, and the difference between maximum and minimum wall heat flux reaches hundreds of times. Then, the transient response was simulated when inlet conditions of primary side were perturbed by step changes, and it was found that maximum wall heat flux increases from 1175.5 kW/m2 to 1365 kW/m2, increasing by nearly 16 %, when inlet lead–bismuth temperature step increases from 450°C to 480 °C.

LC contact lens sensor for ultrasensitive intraocular pressure monitoring

Twenty-four hours continuous intraocular pressure (IOP) monitoring is beneficial for glaucoma care. Contact lens sensors using LC technology can achieve non-invasive continuous IOP measuring around the clock and are relatively simple in principle and structure, thus dominating the mainstream. Among them, stretchable inductive LC contact lens sensors constructed with liquid metal have advantages in signal quality as well as wearing comfort, but currently its sensitivity is slightly insufficient. Here, we propose an LC sensor that constructed with liquid metal to form the stretchable inductance and capacitance further. The capacitive plate and inductive coil can response to IOP changes simultaneously, thus able to enhance the sensitivity in principle. We modeled the sensing mechanism and conducted design, fabrication, as well as various tests. The device exhibits good characteristics, including reliability, good signal quality, etc. Especially, it has a threefold increase in sensitivity, exceeding the current state-of-the-art contact lens sensors.

Corrosion inhibition of Ga-based thermal interface materials with Ni coating on Cu substrate

The gallium (Ga) base liquid metal (LM) with high thermal conductivity and deformability is applied widely in thermal management in electrical systems. However, Ga readily reacts with Cu to form intermetallic compounds (IMCs), which can cause failure in electronic devices. Herein, the thermal interface material (TIM) with Ga and diamond is prepared to analyze the reaction behavior of TIM and Cu/Ni-plated Cu under an aging test at 125 °C. The results show that Ga reacts with Cu substrate and forms CuGa2 bulk. Moreover, Ni coating can inhibit the corrosion of Ga and Cu. However, the as-volcano IMC structures were generated, also. The thermal resistance increased from 2.24 mm2·K·W−1 to 14.47 mm2·K·W−1 from initial time to 200 h. The interfacial corrosion behavior between TIM and Cu substrate is studied by first-principles molecular dynamics simulation. The diffusion coefficient in the z direction of Cu is 0.04 × 10−5 cm2/s. In a word, the work could provide the guidelines for the further design of high-performance corrosion resistance in the region where Ga was used for thermal management on electronic products.

An enclosed solid-liquid triboelectric nanogenerator based on Janus-type TPU nanofibers

Various environmental factors such as high humidity, rain, snow, and other conditions restrict the practical use of triboelectric nanogenerator (TENG). Herein, Janus-type thermoplastic polyurethane (TPU) nanofiber films with good hydrophobicity were fabricated by side-by-side electrospinning. The output performance of TENG based on Janus-type TPU nanofiber films was much higher than that made of normal TPU nanofiber films. A flexible enclosed TENG was prepared that maintained its output performance regardless of external humidity. What’s more, liquid metal gallium (Ga) was injected into the enclosed TENG and used as the tribo-material. The addition of Ga to the enclosed TENG increased its output performance to reach a peak voltage of 282 V and current of 6.0 μA. The enclosed TENG was able to power light-emitting diodes (LEDs) even when immersed in water, demonstrating its potential for using under high-humidity conditions.

Oxidation-Induced Oxide Shell Rupture and Phase Separation in Eutectic Gallium-Indium Nanoparticles.

Eutectic gallium-indium (EGaIn), a room-temperature liquid metal, has garnered significant attention for its applications in soft electronics, multifunctional materials, energy engineering and drug delivery. A key factor influencing these diverse applications is the spontaneous formation of a native passivating oxide shell that not only encapsulates the liquid metal but also alters the properties from the bulk counterpart. Using environmental scanning transmission electron microscopy, we report in situ observations of the oxidation of EGaIn nanoparticles by ambient air under high-energy electron beam irradiation. Our findings demonstrate that uneven oxide shell growth, driven by inward diffusion of adsorbed O species, creates unbalanced stresses. This compels the liquid metal to deform toward regions with slower oxide growth, resulting in shell rupture and allowing the liquid metal core to flow out. This process initiates top-down self-similar replication of the core-shell liquid metal nanoparticles, causing larger particles to break down into smaller particles. Additionally, internal oxidation triggers phase separation within the liquid core, ultimately leading to the pulverization of the liquid metal into finer solid particles rich in indium. These mechanistic insights into the oxidation behavior of the liquid metal hold practical implications for leveraging this process to reconfigure EGaIn nanoparticles for various applications.

Accuracy and scalability of incompressible inductionless MHD codes applied to fusion technologies

Abstract It is well-known that magnetohydrodynamics (MHD) dominates the dynamic of the liquid metal flows inside the breeding blankets (BB) of future nuclear fusion plants by magnetic confinement. MHD is a multiphysics phenomenon involving both electromagnetism and incompressible fluid mechanics. From the computational point of view, the simulation of MHD flows in fusion relevant conditions entails a significant challenge. Indeed, due to the shape of the induced electrical currents inside the bulk of the fluid, high spatial resolutions are needed to capture the large gradients found in boundary layers and 3D effects. Besides, solving the equations accurately typically requires very small time steps for the transient algorithms. Over the past few decades, some parallel MHD codes have been developed with success to simulate complex flows in increasingly realistic geometries. Among them, the MHD tools of commercial CFD platforms have attracted attention due to their relatively soft learning curve. Most of these codes are based on the so called ϕ-formulation which, by applying the divergence free condition of the current density to the Ohms law, reduces the electromagnetic part of the problem to a single Poisson equation. As a downside, the approach segregates the fluid and electromagnetic problem. In practice, this establishes important limits to the mesh element size, to the mesh quality and to the time-step needed to obtain accurate and stable solutions that maintains charge conservation at a discrete level. In this work, these limits are explored for the commercial platform ANSYS-Fluent using a test geometry under different conditions. As an alternative, a new code based on Finite Element Methods (FEM) is introduced as well. This open-source code, called GridapMHD (https://github.com/gridapapps/GridapMHD.jl), aims at solving the full set of MHD equations using a monolithic approach. GridapMHD is still in early stages of development but it has already shown promising results.

Experimental investigation on magneto-convective flows around two differentially heated horizontal cylinders

Liquid metal buoyant flow around two differentially heated horizontal cylinders in the presence of a uniform vertical magnetic field is investigated experimentally. While magneto-convection in pipes or ducts has been studied theoretically and experimentally in recent years, data for heat transfer at immersed obstacles are rare and, to our knowledge, detailed experimental investigations on this fundamental magnetohydrodynamic problem do not exist. In the present work, two horizontal cylinders inserted into an adiabatic rectangular cavity filled with gallium–indium–tin are kept at constant temperatures to establish a driving temperature gradient in the surrounding liquid metal. The buoyancy-driven flow, quantified by the Grashof number $Gr$ , is varied in the range ${10^{6} \leq Gr \leq ~5\times 10^{7}}$ . With increasing magnetic field, expressed via the Hartmann number $Ha$ , different flow regimes are identified from measurements for $0 \leq Ha \leq ~3000$ . The effect of the electromagnetic force primarily consists in suppressing turbulence and damping the convective flow. The heat transfer is quantified in terms of the non-dimensional Nusselt number $Nu$ , and its dependence on $Gr/{Ha}^{2}$ , which is identified as the important group governing the flow, is discussed.

Heat transport in liquid metal convection from onset to turbulence: the effect of small aspect ratio

Heat transport in liquid metal convection from onset to turbulence: the effect of small aspect ratio

Dynamic Electric Discharge Paths in Liquid Metal Marble Arrays.

Electric discharge occurs ubiquitously in both natural and engineered systems, where the discharge paths provide critical information. However, control and visualization of discharge patterns is a challenging task. Here arrays of liquid metal marbles, droplets of a gallium-indium eutectic alloy with a copper-doped ZnS luminescent coating, are designed for pixelated visualization of electric discharge paths at optical imaging length-scales. The ZnS particles embed themselves into the surface of liquid metal droplets and are anchored by a self-limiting gallium oxide layer. The operation is achieved by generating spark discharges at inter-marble air gaps and reduced voltage drop across highly conducting liquid metal droplets. By taking advantage of the malleability of soft liquid metal marbles, the dynamic visualization platforms allow the manipulation of discharge path selections in configurable marble arrays and the embedding of artificial defect features. The systems are further integrated for characterizing dynamic changes in granular and soft systems, and for enabling logic computing and information encoded display. This demonstration holds promises for creating new-generation electric discharge-based optoelectronics.

Stiffness and Interface Engineered Soft Electronics with Large-Scale Robust Deformability.

Skin-like stretchable electronics emerge as promising human-machine interfaces but are challenged by the paradox between superior electronic property and reliable mechanical deformability. Here, a general strategy is reported for establishing robust large-scale deformable electronics by effectively isolating strains and strengthening interfaces. A copolymer substrate is designed to consist of mosaic stiff and elastic areas with nearly four orders of magnitudes modulus contrast and cross-linked interfaces. Electronic functional devices and stretchable liquid metal (LM) interconnects are conformally attached at the stiff and elastic areas, respectively, through hydrogen bonds. As a result, functional devices are completely isolated from strains, and resistances of LM conductors change by less than one time when the substrate is deformed by up to 550%. By this strategy, solar cells, wireless charging antenna, supercapacitors, and light-emitting diodes are integrated into a self-powered electronic skin that can laminate on the human body and exhibit stable performances during repeated multimode deformations, demonstrating an efficient path for realizing highly deformable energy autonomous soft electronics.

Multi-objective design optimization and physics-based sensitivity analysis of field emission electric propulsion for CubeSat platforms

Field-emission electric propulsion is an electrostatic space electric propulsion technology that offers various advantageous features including efficient design, high specific impulse, and versatile thrust capabilities ranging from micro-Newton to milli-Newton levels. These characteristics make this type of propulsion a promising technology for small satellite platforms, enabling precise attitude control, orbit maintenance, and de-orbiting through ionization and acceleration of a liquid metal propellant. The growing demand for small propulsion systems in CubeSat platforms has spurred significant progress in modeling and characterizing field emission electric propulsion thrusters to enhance their overall performance. However, little study has been conducted to investigate the effect of geometric configurations on electric fields or expelled ion trajectories for design optimization. In this study, multi-objective design optimization is performed by incorporating electrostatic simulation coupled with an analytical performance model into evolutionary algorithms based on prediction from surrogate modeling, aiming to optimize the thruster emission design to maximize thruster performance. Physical insights into the key design factors influencing the performance of field emission electric propulsion have been gained by probing into the interaction between ion particles and electric field behavior within the thruster. It has been found that the length of the emitter tip has a significant effect on plume divergence, i.e., a longer emitter tip under the influence of electric field at higher emitter current tends to result in lower initial acceleration of emitted ions and subsequently wider spread or divergence of the ion beam. A shorter emitter tip, on the other hand, generates a sharper E-field gradient, resulting in a more focused and narrower ion beam. Additionally, sensitivity analysis has identified the mass flow rate and potential distributions as the most influential design factors on performance due to the active roles they play in the performance generation process.

Ternary intermediate phase mediated high energy density and kinetically accelerated Sb-Cd electrode for liquid metal batteries

Liquid metal battery (LMB) is an attractive technology that can address the big challenge of efficient utilization of renewable energies, ascribed to its potential ultralong service lifetime, ideal cost-efficiency, and high safety. However, breaking through the energy density bottleneck remains a persistent challenge, due to the limited lithiation voltage and specific capacity of cathodes. Herein, we design a novel dual-active Sb-Cd cathode, which shows a new ternary alloying discharge mechanism with reversible formation of ternary intermediate phase LiCdSb, accompanied by a high discharge voltage of 1.0 V. Coupled with the excellent Li storage capability of Cd, the Sb80Cd20 cathode attains an attractive capacity (> 500 mAh g-1), outperforming all reported LMB cathodes. More importantly, upon deep lithiation, the conversion reaction of ternary LiCdSb to Li3Sb mediates the regeneration and dispersion of Cd melt in the cathode, which constructs in situ fast electron and lithium diffusion networks for the subsequent discharge, significantly accelerating the electrode reaction kinetics. Thus, the Sb80Cd20 electrode achieves an exceptional combination of high energy density (398.4 Wh kg-1 at 200 mA cm-2) and superior rate capability (542.5 W kg-1 at 2400 mA cm-2). Additionally, the Li||Sb-Cd battery exhibits an outstanding tolerance and self-healing ability towards thermal runaway.

Effects of double diffusion and soret effect on mhd braking of liquid metal packed between enclosed rotating cylindrical annulus

Effects of double diffusion and soret effect on mhd braking of liquid metal packed between enclosed rotating cylindrical annulus

Water-Etched Porous Ti: Surface Manipulation of Ti Foam Fabricated by Liquid Metal Dealloying Technique.

The liquid metal dealloying (LMD) process enables the fabrication of porous metals with various chemical compositions. Despite its advantages, LMD still faces key challenges such as maintaining the high-temperature molten metal bath for a prolonged time, avoiding the use of toxic etchants, and so on. To overcome these challenges, the study develops a water-leachable and oxidation-resistant alloy melt (AM) in Ca-Mg binary system. Specifically, Ca72Mg28 eutectic AM is designed, which exhibits higher oxidation resistance and lower melting temperature compared to pure Mg, allowing LMD to be conducted in atmospheric conditions as well as temperatures >200K lower. The AM also enables an innovative process to fabricate Ti foams with a hexagonal faceted surface structure by carefully manipulating the etching rate during the water etching process. This approach allows for the creation of foam with a surface area over 13% larger than that of foams with smooth surfaces via normal acid etching, potentially enhancing efficiency in applications such as electrodes for electrochemical systems or biomedical materials where increased cell adhesion can be beneficial. This study paves the way for efficiently manipulating the LMD process to fabricate metal foams with customized compositions and enhanced surface properties.

Disordered non-Fermi liquid fixed point for two-dimensional metals at Ising-nematic quantum critical points

Understanding the influence of quenched random potential is crucial for comprehending the exotic electronic transport of non-Fermi liquid metals near metallic quantum critical points. In this study, we identify a stable fixed point governing the quantum critical behavior of two-dimensional non-Fermi liquid metals in the presence of a random potential disorder. By performing renormalization group analysis on a dimensional-regularized field theory for Ising-nematic quantum critical points, we systematically investigate the interplay between random potential disorder for electrons and Yukawa-type interactions between electrons and bosonic order-parameter fluctuations in a perturbative epsilon expansion. At the one-loop order, the effective field theory lacks stable fixed points, instead exhibiting a runaway flow toward infinite disorder strength. However, at the two-loop order, the effective field theory converges to a stable fixed point characterized by finite disorder strength, termed the “disordered non-Fermi liquid (DNFL) fixed point”. Our investigation reveals that two-loop vertex corrections induced by Yukawa couplings are pivotal in the emergence of the DNFL fixed point, primarily through screening disorder scattering. Additionally, the DNFL fixed point is distinguished by a substantial anomalous scaling dimension of fermion fields, resulting in pseudogap-like behavior in the electron’s density of states. These findings shed light on the quantum critical behavior of disordered non-Fermi liquid metals, emphasizing the indispensable role of higher-order loop corrections in such comprehension.

Liquid metal induced segregated-like electromagnetic shielding composites with excellent photothermal conversion and strain sensing capacities

The development of multifunctional electromagnetic interference (EMI) shielding materials has garnered significant attention, yet achieving flexible composites that integrate EMI shielding, thermal conductivity, and other functionalities under low filler loading remains a challenge. This study presents a novel flexible composite with segregated structure prepared via a simple co-mixing and hot-pressing method. By selectively distributing conductive Liquid metal (LM) and Multi-wall carbon nanotube (CNT) on the surface of Polyurethane (TPU) particles, a continuous and compact conductive network is successfully constructed, enabling the attainment of a high EMI shielding effectiveness of 80.2 dB and a thermal conductivity of 4.8 W m−1 K−1 even at low LM loadings. Furthermore, the composite exhibits low-voltage-driven Joule heating performance, excellent photothermal conversion efficiency, and promising potential for wearable sensor applications. The combination of these outstanding properties highlights the great potential of LM-based composites for next-generation wearable devices.

Hetero phase nanocomposite based posture sensor with stretchable connector-sensor interface

During recent years, stretchable and flexible sensors for wearable application have gained a lot of interest, but one of the grand challenges that yet to be addressed is the interface between the soft and stretchable sensor and the hard and rigid circuits. The mechanical mismatch between soft sensors and hard connectors to external circuits makes the interface prone to quick failure under mechanical strain and deformation.Here, we report a soft piezoresistive posture sensor made of a hetero-phase nanocomposite with the stretchable connector-sensor interface for the robust sensing of the posture. The hetero-phase nanocomposite is made of Gallium-indium (GaIn) in the liquid phase, carbon nano tube (CNT) and polydimethylsiloxane (PDMS) in the solid phase. The sensor with the Young’s modulus of 158 kPa shows comparable mechanical softness to the skin, which is essential for accurate sensing. Further, we developed liquid metal (LM) based stretchable connections between the soft sensor and the connectors to the external circuit to enable the stable operation of the sensor under deformation. The developed posture sensor has a gauge factor (GF) of 0.815 under 20 % and 0.32 between 20 % and 60 % of applied tensile strain. The sensor was successfully used for sensing of the posture with the sensitivity of 1 % change in its electrical resistance per 10 degrees of neck tilting and strain sensitivity of 2 % of applied strain. The fabrication of the CNT-LM-PDMS posture sensor employed a scalable and cost-effective process. The presented stretchable connection is a solution that can be applied to many soft and stretchable wearable sensors and circuit interfaces with various physiological sensing applications.

Preparation of 2D AlxGa1-xN film via printing liquid metals

AlGaN film is a promising barrier layer widely used in high electron mobility transistor. Facile preparation of 2D AlGaN with high quality is still a challenge for traditional process. In this work, high quality 2D AlxGa1-xN (mixture of AlN and GaN) is synthesized by using liquid alloy printing technique and post nitriding treatment. The prepared 2D AlxGa1-xN shows good crystallinity and ultra-wide bandgap of 5.55 eV. Besides, the 2D AlxGa1-xN is a n-type semiconductor and can act as channel layer in field effect transistor. This novel process provides a facile way to obtain 2D AlxGa1-xN film, which will have a potential application in AlGaN/GaN heterostructure field effect transistors.