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Magnetic liquid metal (MLM) is a mixture of magnetic particles with gallium‐based liquid metals which utilizes an unconventional combination of fluidity, high thermal/electrical conductivity, biocompatibility, and magnetism. Recently, from materials to applications, studies on MLMs have drastically increased. Single or multiple MLMs can be precisely positioned or can act as a carrier for handling other objects. MLMs are also used in biomedical applications such as cancer treatment by hyperthermia and precision delivery of cancer drugs on tumors, or antibacterial coating which kills bacteria. In electronics applications, MLMs are used for magnetic field‐driven patterning of metallic lines, reconfigurable interconnects, electronic tattoos, and reconfigurable electromagnetic wave shielding. Phase change (solid/liquid) of MLMs adds another unique capability, morphing. A combination of innovations in the micro/nano robots and MLMs has huge potential to bring an unprecedented disruptive technology for a wide variety of applications including self‐morphing shape‐recovery robots, highly localized cancer treatment, and reconfigurable stealth/camouflage, among others. This article comprehensively reviews recent developments in MLMs from the materials to methods of preparation, locomotion of MLMs, their applications, and future outlooks. [ABSTRACT FROM AUTHOR]

Thermal transport is of grave importance in many high-value applications. Heat dissipation can be improved by utilizing liquid metals as thermal interface materials. Yet, liquid metals exhibit corrosivity towards many metals used for heat sinks, such as aluminum, and other electrical devices (i.e., copper). The compatibility of the liquid metal with the heat sink or device material as well as its long-term stability are important performance variables for thermal management systems. Herein, the compatibility of the liquid metal Galinstan, a eutectic alloy of gallium, indium, and tin, with diamond coatings and the stability of the liquid metal in this environment are scrutinized. The liquid metal did not penetrate the diamond coating nor corrode it. However, the liquid metal solidified with the progression of time, starting from the second year. After 4 years of aging, the liquid metal on all samples solidified, which cannot be explained by the dissolution of aluminum from the titanium alloy. In contrast, the solidification arose from oxidation by oxygen, followed by hydrolysis to GaOOH due to the humidity in the air. The hydrolysis led to dealloying, where In and Sn remained an alloy while Ga separated as GaOOH. This hydrolysis has implications for many devices based on gallium alloys and should be considered during the design phase of liquid metal-enabled products. [ABSTRACT FROM AUTHOR]

Directed liquid metal (gallium‐based) manipulation and actuation are paramount for copious applications, including soft robotics, soft electronics, and targeted drug delivery. Although there are several strategies available to achieve mobility of liquid metals in a "wet" environment. Strategies to achieve and improve mobility of liquid metal droplets and puddles in a "dry" environment are scarce and rely on metallophobic surface design or liquid metal marbles. Here, high mobility of Galinstan is elucidated by combining metallophobic surface design and vertical vibrations. Vibration frequencies between 20 and 30 Hz are conducive to droplet movement and threshold inclination angles of 0.5° to 1° are observed upon actuation by these vibrations. The method itself is applicable for a wide range of droplet sizes (30 and 2000 µL) and very robust. The droplet movement typically comprises of periodic receding and advancing of the droplet and commences via a rolling mechanism rather than a gliding mechanism. Finally, it is shown that small (0.5 mm height) obstacles can be traversed by this method, indicating that it can be used in concert with other strategies, such as surface structuring strategies, which open up pathways for mobility and controlled actuation of liquid metal droplets in air. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RISs) have the potential to improve wireless communication links by dynamically redirecting signals to dead spots. Although a reconfigurable surface is best suited for environments in which the reflected signal must be dynamically steered, there are cases where a static, non-reconfigurable anomalous reflective metasurface can suffice. In this work, spray-coated liquid metal is used to rapidly prototype an anomalous reflective metasurface. Using a pressurized air gun and a plastic thin-film mask, a metasurface consisting of a 6 × 4 array of Galinstan liquid–metal elements is sprayed within minutes. The metasurface produces a reflected wave at an angle of 28° from normal in response to a normal incident 3.5-GHz electromagnetic plane wave. The spray-coated liquid–metal metasurface shows comparable results to an anomalous reflective metasurface with copper elements of the same dimensions, demonstrating that this liquid–metal fabrication process is a viable solution for the rapid prototyping of anomalous reflective metasurfaces. [ABSTRACT FROM AUTHOR]

In diesem Beitrag werden neue Experimente zu Redoxreaktionen an der Oberfläche von Flüssigmetalle vorgestellt, wobei das Flüssigmetall entweder als Reduktionsmittel oder als Reaktionsumgebung Verwendung findet. Daher werden hier die Themenfelder „Redoxreaktionen" sowie „Standardpotentiale" und „Metallurgie" miteinander verknüpft. Die Versuche bestechen durch ihren einfachen Aufbau, einfach Handhabbarkeit, da keine gefährlichen Chemikalien verwendet werden, den schnellen visuellen und einprägsamen Zugang zu Redoxreaktionen und die Wiederverwendbarkeit des Flüssigmetalls (Galinstan). [ABSTRACT FROM AUTHOR]

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Centrifugal Nuclear Thermal Propulsion is a second-generation propulsion concept currently being researched to succeed traditional solid core nuclear thermal propulsion. Current efforts across the space industry are focusing on development of technologies for enabling manned flight to Mars and scientific missions to the outer planets. To enable these types of mission's direct injection trajectories are needed to decrease exposure to astronauts and scientific payloads to the harsh environment of space. Current efforts in nuclear thermal propulsion have shown great promise in higher specific impulses ∼900 s, but even these levels of specific impulse fall short for manned Mars missions with durations less than two years or direct injection to orbit of the outer ice giants Uranus and Neptune without the use of gravity assists. High performance nuclear thermal propulsion has been proposed using bubble through nuclear reactors to reach specific impulses as high as 1800 s, however significant challenges exist to prove the feasibility of such a system. One of the major challenges is the fluid mechanics within the core of the engine since little is known about uranium in the liquid phase. An experimental study has been conducted to better understand the fluid dynamics to better inform the thermodynamic and nucleonic models. Using the data from the experiment, high-fidelity simulations have been developed to predict the fluid dynamics of the uranium fuel. This information can then be further fed into thermodynamics models in development to predict core temperatures and system behaviour. The validated models show that small bubbles reach thermal equilibrium, and high centrifugal forces and surface tension assist in confining the molten uranium within the reactor core. Injector methods suggest feasible configurations to encourage bubble flow while minimizing backflow of the propellant, motivating further study of Centrifugal Nuclear Thermal Propulsion based systems. • Galinstan (Ga67In20.5Sn12.5) was determined to be a suitable uranium simulant for bubble formation. • High Speed Radiography was used to determine bubble characteristics using machine learning algorithm. • Hydrogen bubbles in uranium rapidly reach local equilibrium with diameters of 0.266 mm and reaching velocities of 16 m/s. • To date all research indicates that a centrifugal nuclear thermal rocket is feasible. [ABSTRACT FROM AUTHOR]

The heat transfer rate of magnetocaloric regenerators is a topic of extensive research and the cyclability of these regenerators is critical to the operation of systems with a high coefficient of performance (e.g., potentially >22, significantly higher than typical vapor compression cooling technologies). To enable a high operating frequency that will result in a high specific cooling power, the heat transfer fluid should have high thermal conductivity and lower specific heat, i.e., higher thermal diffusivity. Eutectic metal alloys possess these qualities, such as gallium–indium–tin (Galinstan), whose thermal diffusivity has been found to be approximately an order of magnitude higher than water. For this study, the effects of eutectic liquid Galinstan exposure on the phase stability of LaFe13−x−yMnxSiyH1.6 magnetocaloric powders in an active magnetic regenerator device were investigated. The powders were characterized before and after exposure to Galinstan using X-ray diffraction, in which the phases were determined using the Rietveld refinement technique and X-ray fluorescence. It was found that after Galinstan exposure, hydrogen containing phases were present in the powder, suggesting that the hydrogen was lost from the magnetocaloric phase. The magnetocaloric phase degradation indicates that the powder was incompatible with the Galinstan metal in an environment with moisture. [ABSTRACT FROM AUTHOR]

The need for effective cooling of microprocessors, whose processing speed is increasing, is also increasing at the same rate. This increases the work on more effective cooling methods. Mini/micro-channel heat sinks cooled with liquid metals can provide effective cooling due to their high heat conductivity. In this study, the impact of using fins on the thermal resistance coefficient and the resulting pressure drop in a mini-channel heat sink cooled with Galinstan is investigated. As a result of the numerical analysis created by the arrangement of the fins in the channel in different configurations and consisting of a total of 70 different models, no significant thermal performance improvement is observed when the distance between the fins is less than 1.5 mm, but it has been determined that excessive pressure drop occurs. When the fin length is 0.3 mm and the distance between the fins is 1.5 mm, a thermal performance improvement of 15.9% was obtained in the minimum fluid inlet velocity condition compared to the case without fins. On the other hand, there was an increase in pressure loss of 95 kPa in this case. [ABSTRACT FROM AUTHOR]

The need for new heat transfer agent for many applications, namely in the consumer electronics industry, requires materials, liquids at room temperature, with high thermal conductivity. From the different possibilities, Galinstan, a eutectic alloy of Gallium, Indium, and Tin with a melting point (Tm = 283.4 K) has been proposed for many applications, namely for replacing the toxic mercury element, used for many years. It is the purpose of this paper to report thermal conductivity measurements of Galinstan, product name Gallium/Indium/Tin Eutectic (NL-011), Ga68.4In21.5Sn10. The method used was the transient hot strip (THS), using a platinum metal-film sensor, produced by PVD in ceramic substrates, and electrically insulated with a heat-shrinkable coating. The details of the data acquisition system and measuring procedure are reported. Measurements were performed between 28 °C and 103 °C (301 K to 376 K), at atmospheric pressure, with an estimated uncertainty of 6%, and compared with available literature. Data were correlated for linear interpolation. This type of sensor is applied to molten metals for the first time, proofing to concept to future applications in molten metals and molten salts at higher temperatures. [ABSTRACT FROM AUTHOR]

Thermal transport is of grave importance in many high-value applications. Heat dissipation can be improved by utilizing liquid metals as thermal interface materials. Yet, liquid metals exhibit corrosivity towards many metals used for heat sinks, such as aluminum, and other electrical devices (i.e., copper). The compatibility of the liquid metal with the heat sink or device material as well as its long-term stability are important performance variables for thermal management systems. Herein, the compatibility of the liquid metal Galinstan, a eutectic alloy of gallium, indium, and tin, with diamond coatings and the stability of the liquid metal in this environment are scrutinized. The liquid metal did not penetrate the diamond coating nor corrode it. However, the liquid metal solidified with the progression of time, starting from the second year. After 4 years of aging, the liquid metal on all samples solidified, which cannot be explained by the dissolution of aluminum from the titanium alloy. In contrast, the solidification arose from oxidation by oxygen, followed by hydrolysis to GaOOH due to the humidity in the air. The hydrolysis led to dealloying, where In and Sn remained an alloy while Ga separated as GaOOH. This hydrolysis has implications for many devices based on gallium alloys and should be considered during the design phase of liquid metal-enabled products.

Reconfigurable intelligent surfaces (RISs) have the potential to improve wireless communication links by dynamically redirecting signals to dead spots. Although a reconfigurable surface is best suited for environments in which the reflected signal must be dynamically steered, there are cases where a static, non-reconfigurable anomalous reflective metasurface can suffice. In this work, spray-coated liquid metal is used to rapidly prototype an anomalous reflective metasurface. Using a pressurized air gun and a plastic thin-film mask, a metasurface consisting of a 6 × 4 array of Galinstan liquid–metal elements is sprayed within minutes. The metasurface produces a reflected wave at an angle of 28° from normal in response to a normal incident 3.5-GHz electromagnetic plane wave. The spray-coated liquid–metal metasurface shows comparable results to an anomalous reflective metasurface with copper elements of the same dimensions, demonstrating that this liquid–metal fabrication process is a viable solution for the rapid prototyping of anomalous reflective metasurfaces.

The heat transfer rate of magnetocaloric regenerators is a topic of extensive research and the cyclability of these regenerators is critical to the operation of systems with a high coefficient of performance (e.g., potentially >22, significantly higher than typical vapor compression cooling technologies). To enable a high operating frequency that will result in a high specific cooling power, the heat transfer fluid should have high thermal conductivity and lower specific heat, i.e., higher thermal diffusivity. Eutectic metal alloys possess these qualities, such as gallium–indium–tin (Galinstan), whose thermal diffusivity has been found to be approximately an order of magnitude higher than water. For this study, the effects of eutectic liquid Galinstan exposure on the phase stability of LaFe13−x−yMnxSiyH1.6 magnetocaloric powders in an active magnetic regenerator device were investigated. The powders were characterized before and after exposure to Galinstan using X-ray diffraction, in which the phases were determined using the Rietveld refinement technique and X-ray fluorescence. It was found that after Galinstan exposure, hydrogen containing phases were present in the powder, suggesting that the hydrogen was lost from the magnetocaloric phase. The magnetocaloric phase degradation indicates that the powder was incompatible with the Galinstan metal in an environment with moisture.

The production of energy has become a major issue in today's world. Triboelectric nanogenerators (TENGs) are promising devices that can harvest mechanical energy and convert it into electrical energy. This study explored the use of Galinstan particles in the production of TENGs, which convert mechanical energy into electrical energy. During the curing process, the evaporation of the hexane solvent resulted in a film with varying concentrations of Galinstan particles. The addition of n-hexane during ultrasonication reduced the viscosity of the polydimethylsiloxane (PDMS) solution, allowing for the liquid metal (LM) particles to be physically pulverized into smaller pieces. The particle size distribution of the film with a Galinstan concentration of 23.08 wt.% was measured to be within a few micrometers through ultrasonic crushing. As the amount of LM particles in the PDMS film increased, the capacitance of the film also increased, with the LM/PDMS film with a 23.08% weight percentage exhibiting the highest capacitance value. TENGs were created using LM/PDMS films with different weight percentages and tested for open-circuit voltage, short-circuit current, and charge amount Q. The TENG with an LM/PDMS film with a 23.08% weight percentage had the highest relative permittivity, resulting in the greatest voltage, current, and charge amount. The use of Galinstan particles in PDMS films has potential applications in wearable devices, sensors, and biomedical fields. [ABSTRACT FROM AUTHOR]

Gallium alloys are ideal base carriers for temperature-sensitive ferrofluids, which can be used for energy convection, soft robotics, microchannels, magnetorheological devices, etc. In this study, gallium was mixed with different substances (In, Sn, Zn, Ge, and Al) to obtain a low melting point, reduce the wetness and adhesion of its alloys, and realize low viscosity. The melting point, contact angle on certain solid plates, viscosity, and viscoelasticity of the gallium alloys were measured, and some useful gallium alloys were obtained. The experimental results showed that Ga80In10Sn10 had lower wettability at a larger contact angle of 148.6° on the Teflon plate. Here, (Ga80In10Sn10)97Zn3 with a melting point of 8.2 °C, lower than the melting point of Galinstan, was developed. It had a viscosity about three times that of water at room temperature and an elastic response from 0.1 to 100 Hz at a 1% strain amplitude for the viscoelasticity. It was expected that a kind of temperature-sensitive magnetic fluid with a gallium-based liquid alloy as the base carrier liquid would be prepared in the future with Teflon as the container to achieve energy conversion under the drive of the magnetic field. [ABSTRACT FROM AUTHOR]

Mini/microchannel cooling performance can be improved with microencapsulated phase change material (MPCM) slurry as coolant by utilizing latent heat absorption capacity of MPCM. Compared with existing water, using liquid metal (LM) as basefluid can combine the advantages of high apparent heat capacity of MPCM particles and high thermal conductivity of LM. Thus, the prepared MPCM-LM slurry is proposed as coolant for minichannel heat sink. The melting of particles near the bottom enhances heat transfer performance of two-phase MPCM-LM slurry, but migration and aggregation cause the increase of pressure drop. Furthermore, the two-phase model is adopted to investigate the melting behavior and migration characteristics of MPCM particles in galinstan flow and the effect of particle volume percent on minichannel cooling performance. The results show that particles present boundary-to-center melting behavior in MPCM-galinstan slurry, resulting in the larger reduction degree in bulk mean temperature compared to MPCM-water slurry. Different from uniform distribution for small-diameter particles, the large-diameter particles migrate upward, leading to top-aggregation distribution and up-down asymmetry of velocity profile. Finally, the increase of particle volume percent significantly reduces heat capacity thermal resistance of heat sink, and maximum reduction is 59.02% for MPCM-galinstan slurry with φs = 20% compared to pure galinstan.

The production of energy has become a major issue in today’s world. Triboelectric nanogenerators (TENGs) are promising devices that can harvest mechanical energy and convert it into electrical energy. This study explored the use of Galinstan particles in the production of TENGs, which convert mechanical energy into electrical energy. During the curing process, the evaporation of the hexane solvent resulted in a film with varying concentrations of Galinstan particles. The addition of n-hexane during ultrasonication reduced the viscosity of the polydimethylsiloxane (PDMS) solution, allowing for the liquid metal (LM) particles to be physically pulverized into smaller pieces. The particle size distribution of the film with a Galinstan concentration of 23.08 wt.% was measured to be within a few micrometers through ultrasonic crushing. As the amount of LM particles in the PDMS film increased, the capacitance of the film also increased, with the LM/PDMS film with a 23.08% weight percentage exhibiting the highest capacitance value. TENGs were created using LM/PDMS films with different weight percentages and tested for open-circuit voltage, short-circuit current, and charge amount Q. The TENG with an LM/PDMS film with a 23.08% weight percentage had the highest relative permittivity, resulting in the greatest voltage, current, and charge amount. The use of Galinstan particles in PDMS films has potential applications in wearable devices, sensors, and biomedical fields.

The ability to control interfacial tension electrochemically is uniquely available for liquid metals (LMs), in particular gallium‐based LM alloys. This imparts them with excellent locomotion and deformation capabilities and enables diverse applications. However, electrochemical oxidation of LM is a highly dynamic process, which often induces Marangoni instabilities that make it almost impossible to elongate LM and manipulate its morphology directly and precisely on a 2D plane without the assistance of other patterning methods. To overcome these limitations, this study investigates the use of an LM–iron (Fe) particle mixture that is capable of suppressing instabilities during the electrochemical oxidation process, thereby allowing for superelongation of the LM core of the mixture to form a thin wire that is tens of times of its original length. More importantly, the elongated LM core can be manipulated freely on a 2D plane to form complex patterns. Eliminating Marangoni instabilities also allows for the effective spreading and filling of the LM–Fe mixture into molds with complex structures and small features. Harnessing these excellent abilities, a channel‐less patterning method for fabricating elastomeric wearable sensors is demonstrated to detect motions. This study shows the potential for developing functional and flexible structures of LM with superior performance. [ABSTRACT FROM AUTHOR]

Abstract The ability to control interfacial tension electrochemically is uniquely available for liquid metals (LMs), in particular gallium‐based LM alloys. This imparts them with excellent locomotion and deformation capabilities and enables diverse applications. However, electrochemical oxidation of LM is a highly dynamic process, which often induces Marangoni instabilities that make it almost impossible to elongate LM and manipulate its morphology directly and precisely on a 2D plane without the assistance of other patterning methods. To overcome these limitations, this study investigates the use of an LM–iron (Fe) particle mixture that is capable of suppressing instabilities during the electrochemical oxidation process, thereby allowing for superelongation of the LM core of the mixture to form a thin wire that is tens of times of its original length. More importantly, the elongated LM core can be manipulated freely on a 2D plane to form complex patterns. Eliminating Marangoni instabilities also allows for the effective spreading and filling of the LM–Fe mixture into molds with complex structures and small features. Harnessing these excellent abilities, a channel‐less patterning method for fabricating elastomeric wearable sensors is demonstrated to detect motions. This study shows the potential for developing functional and flexible structures of LM with superior performance.

Gallium alloys are ideal base carriers for temperature-sensitive ferrofluids, which can be used for energy convection, soft robotics, microchannels, magnetorheological devices, etc. In this study, gallium was mixed with different substances (In, Sn, Zn, Ge, and Al) to obtain a low melting point, reduce the wetness and adhesion of its alloys, and realize low viscosity. The melting point, contact angle on certain solid plates, viscosity, and viscoelasticity of the gallium alloys were measured, and some useful gallium alloys were obtained. The experimental results showed that Ga80In10Sn10 had lower wettability at a larger contact angle of 148.6° on the Teflon plate. Here, (Ga80In10Sn10)97Zn3 with a melting point of 8.2 °C, lower than the melting point of Galinstan, was developed. It had a viscosity about three times that of water at room temperature and an elastic response from 0.1 to 100 Hz at a 1% strain amplitude for the viscoelasticity. It was expected that a kind of temperature-sensitive magnetic fluid with a gallium-based liquid alloy as the base carrier liquid would be prepared in the future with Teflon as the container to achieve energy conversion under the drive of the magnetic field.

Soft and stretchable electronic devices are expected to offer technological advances in the field of robotics, human–machine interfacing, and healthcare. Employing biodegradable elastomers, hydrogels, and nontoxic conductors would add significant value to and minimize the ecological impact of such disposable and transient electronic applications. Here, the biodegradable and photo‐crosslinkable elastomer poly(glycerol sebacic) acrylate (PGSA) is characterized for its use in soft and stretchable electronics. Its mechanical properties are investigated in terms of their chemical composition and compared to commonly used gelatin hydrogels. Furthermore, these materials are combined with interconnects made of liquid Galinstan in order to create functional substrates with certified biodegradability under ISO standards. The combination of these materials produces elastic circuit boards that act as soft platforms for body‐mounted sensors or biodegradable stretchable light‐emitting devices. These soft platforms reveal linear elongations at a break of 130% to 350% and similar moduli to nondegradable elastomers and human tissue, without any decrease in conductivity. Advanced applications in biofriendly packaging, soft robotics, and healthcare will greatly benefit from these biodegradable devices. [ABSTRACT FROM AUTHOR]

A versatile liquid metal (LM) printing process enabling the fabrication of various fully printed devices such as intra‐ and interconnect wires, resistors, diodes, transistors, and basic circuit elements such as inverters which are process compatible with other digital printing and thin film structuring methods for integration is presented. For this, a glass capillary‐based direct‐write method for printing LMs such as eutectic gallium alloys, exploring the potential for fully printed LM‐enabled devices is demonstrated. Examples for successful device fabrication include resistors, p–n diodes, and field effect transistors. The device functionality and easiness of one integrated fabrication flow shows that the potential of LM printing is far exceeding the use of interconnecting conventional electronic devices in printed electronics. [ABSTRACT FROM AUTHOR]

Gallium-based liquid metals have attracted attention as a conductive adaptable material that can be shaped to obtain reconfigurability. We demonstrate a two-dimensional array of liquid-metal conductive nodes, in which reconfigurability is achieved by merging and splitting adjacent nodes to reversibly shape a two-dimensional structure. The nodes are reconfigured using three different actuation schemes: 1) pressure-point actuation, where the liquid metal is actuated by pressing on the flexible superstrate; 2) surface-tension self-splitting, where the geometric shape of the node itself exerts a separating force on merged nodes; and 3) electrocapillary actuation where the liquid metal is actuated by a DC electrical signal. This is the first demonstration of a reconfigurable liquid-metal pixel array using liquid-liquid interconnects for prototyping reconfigurable devices. As a proof of concept, the proposed actuation techniques are used to reconfigure a liquid-metal nodal patch antenna, in which the liquid-metal nodes are reversibly connected and disconnected to change the operating frequency and polarization.

The concept of a reconfigurable 5GHz microfluidically actuated antenna with beam forming, steering and hoping in a 360° angular range, is presented in this paper. Its architecture is that of a Yagi‐Uda array. Its actuation relies on the electrically controlled vertical displacement of liquid metal slugs inside microfluidic channels without the need of any external actuator. Simulations results along two fabricated proofs of concept investigating RF and microfluidic actuation performances are presented. This paper aims at demonstrating the technical soundness and interest of this design for applications such as autonomous sensors networks. [ABSTRACT FROM AUTHOR]

As stretchable devices become well established for applications in soft robotics and wearable devices, the compliant conductors that make these applications possible must also be reliable and survive for the entire device lifetime. Liquid metals such as Galinstan are a potential solution as non‐toxic, stretchable, and low‐resistance conductors. Rigorous investigations of liquid metal lifetimes, however, are limited. This work presents the median lifetime of liquid metal‐filled silicone tubes under current density on the order of 1 kAcm−2, which is necessary for applications such as electromagnetic actuators. In these conductors, the median lifetime increases by a factor of over 4700 as current decreases from 2 to 1 kAcm−2. By cooling the sample, median failure time increases from 112 s to 9.4 h, which suggests straightforward solutions to maximize liquid metal wire lifetime by increasing thermal conductivity or by duty cycling the applied current. [ABSTRACT FROM AUTHOR]

Cellular mechanical properties are closely related to cell physiological functions and status, and their analysis and measurement help understand cell mechanism. In this study, a microfluidic platform was built to measure the mechanical properties of cells by using dielectrophoretic (DEP) force. The electrodes generally used to stretch cells are made of indium tin oxide, Au, and Pt, which have inherent disadvantages. In this paper, galinstan alloy liquid metal was first introduced as microelectrode to form non-uniform electric filed for red blood cell stretching manipulation. The liquid metal microelectrode is easy to manufacture, low in price, stable at high voltage, and reusable. An effective microfluidic chip integrated with liquid metal electrode was designed and simulated, and a series of experiments to capture and stretch red blood cells was performed. The length of the red blood cells increased from 6 μm to 8 μm under the DEP force from 0 pN to 103 pN. This work also revealed the potential use of liquid metal as microelectrode to manipulate the microparticles and cells in a microfluidic chip.

This review focuses on surface modifications to gallium‐based liquid metals (LMs), which are stretchable conductors with metallic conductivity and nearly unlimited extensibility due to their liquid nature. Despite the enormous surface tension of LM, it can be patterned into nonspherical shapes, such as wires, due to the presence of a native oxide shell. Incorporating inherently soft LM into elastomeric devices offers comfort, mechanical compliance, and stretchability. The thin oxide layer also enables the formation of stable liquid colloids and LM micro/nanosized droplets that do not coalesce easily. The oxide layer can also be exfoliated and chemically modified into semiconductor 2D materials to create and deposit atomically thin materials at room temperature. Thus, the interface and its manipulation are important. This review summarizes physical and chemical methods of modifying the surface of LM to tune its properties. The surface modification of LM provides unique applications, including use in soft biomedical sensors and actuators with mechanical properties similar to human tissue.

This review focuses on surface modifications to gallium‐based liquid metals (LMs), which are stretchable conductors with metallic conductivity and nearly unlimited extensibility due to their liquid nature. Despite the enormous surface tension of LM, it can be patterned into nonspherical shapes, such as wires, due to the presence of a native oxide shell. Incorporating inherently soft LM into elastomeric devices offers comfort, mechanical compliance, and stretchability. The thin oxide layer also enables the formation of stable liquid colloids and LM micro/nanosized droplets that do not coalesce easily. The oxide layer can also be exfoliated and chemically modified into semiconductor 2D materials to create and deposit atomically thin materials at room temperature. Thus, the interface and its manipulation are important. This review summarizes physical and chemical methods of modifying the surface of LM to tune its properties. The surface modification of LM provides unique applications, including use in soft biomedical sensors and actuators with mechanical properties similar to human tissue. [ABSTRACT FROM AUTHOR]

Unlike conventional microelectromechanical systems (MEMS), machines based on gallium liquid metal alloys rely on Marangoni flows to induce motion without mechanical moving parts. Despite this advantage, currently developed liquid metal enabled robotic systems still need the locomotion of liquid metal droplets, thereby generating weak actuating forces and limiting their manoeuvrability. Here, a liquid metal engine (LME) is created to work as a jet thruster to continuously power a robot boat without the need of locomotion. In addition, the engine is electrically driven by surface tension without any mechanical moving parts. The structural design and the parameters of operation of the LME are investigated and optimized. Finally, the manipulation of the LME using a motor control unit is demonstrated for driving an untethered robot boat to realize complex locomotion with the precise control over the direction and speed. Thus, this LME could offer new opportunities for developing high‐performance liquid metal machines to power robotic systems. [ABSTRACT FROM AUTHOR]

Despite considerable research efforts, the influence of contact line tension during wetting at the nanoscale and its experimental determination remain challenging tasks. So far, molecular dynamics simulations and atomic force microscope measurements have contributed to the understanding of these phenomena. However, a direct measurement of the size dependence of the contact angle and the magnitude of the apparent line tension has not been realized so far. Here, we show that the contact angle is indeed dependent on the drop size for small drop diameters and determine the magnitude of the apparent line tension via liquid-metal based measurements of advancing and receding contact angle inside a scanning electron microscope. For this purpose, a robotic setup inside an electron microscope chamber and oxide-free Galinstan droplets—produced via an electromigration-based and focused ion beam irradiation-assisted process—are employed. Using the first-order correction of Young’s equation, we find an apparent line tension value of 4.02 × 10−7 J/m for Galinstan© on stainless steel.

We report magnetic field-driven dynamic morphological change of a liquid metal droplet: deformation and recovery; separation and merge. Low melting, non-toxic gallium-based liquid metal has been widely investigated due to its material properties and thus utilized to various applications. Morphological change of the liquid metal in required to tune characteristics of application. In order to enable the liquid metal to be non-wettable and magnetically controllable, we coated the surface with ferromagnetic iron (Fe) particles using hydrochloric acid (HCl) solution resulting in a magnetic liquid metal marble. With and without magnetic field, Fe particles-coated magnetic liquid metal marble was deformed and recovered readily. Against $\sim 8~\mu \text{L}$ magnetic liquid metal marble, depending on the coated Fe particles mass, the shape deformation under magnetic field was changed: conventional (Fe < 4mg) and arbitrary (Fe $\geqq ~4$ mg) wetting shape. Accordingly, the deformability and recovery time of the magnetic liquid metal marble were varied. With an applied magnetic field, one marble was readily separated into 2, 3, and 4 marbles. Due to re-oxidation of the magnetic liquid metal marble surface, we treated the marble with HCl solution and vapor. Split and merge occurred depending on treatment time of HCl solution or vapor. Finally, we demonstrated magnetic field-based dynamic behavior which is reversible. [2020-0218] [ABSTRACT FROM AUTHOR]

We have obtained interfacial properties of Galinstan, a nontoxic liquid-metal alloy, to help replace mercury in miniature devices. To prevent formation of an oxide skin that severely hinders the fluidic behavior of small Galinstan droplets and leads to inaccurate property data, we performed our experiments in a nitrogen-filled glove box. It was found that only if never exposed to oxygen levels above 1 part per million (ppm) would Galinstan droplets behave like a liquid. Two key properties were then investigated: contact angles and surface tension. Advancing and receding contact angles of Galinstan were measured from sessile droplets on various materials: for example, 146.8 ° and 121.5 °, respectively, on glass. Surface tension was measured by the pendant-drop method to be 534.6 ± 10.7 mN/m. All the measurements were done in nitrogen at 28 ° C with oxygen and moisture levels below 0.5 ppm. To help design droplet-based microfluidic devices, we tested the response of Galinstan to electrowetting-on-dielectric actuation. © 2012 IEEE.

Galinstan, a liquid metal at room temperature, is a promising material for use in flexible electronics. Since it has been successfully integrated in devices for external use, e.g., as stretchable electronic skin in tactile sensation, the possibility of using galinstan for flexible implant technology comes to mind. Usage of liquid metals in a flexible implant would reduce the risk of broken conductive pathways in the implants and therefore reduce the possibility of implant failure. However, the biocompatibility of the liquid metal under study, i.e., galinstan, has not been proven in state-of-the-art literature. Therefore, in this paper, a material combination of galinstan and silicone rubber is under investigation regarding the success of sterilization methods and to establish biocompatibility testing for an in vivo application. First cell biocompatibility tests (WST-1 assays) and cell toxicity tests (LDH assays) show promising results regarding biocompatibility. This work paves the way towards the successful integration of stretchable devices using liquid metals embedded in a silicone rubber encapsulant for flexible surface electro-cortical grid arrays and other flexible implants.

Microwave split ring resonators (SRRs) are limited in modern designs to give a fixed resonant response based on their dimensions and material makeup. By designing an adjustable liquid metal component integrated in a highly coupled modified SRR, a frequency-tunable resonator structure was developed. The liquid metal integrated resonators were simulated to show that by varying the amount of liquid metal introduced to the system, the resonant frequency was continuously adjusted from 3.4 to 2.3 GHz, with a consistent resonant amplitude and quality factor of −22 dB and 75, respectively. The frequency-configurable sensor was fabricated with simple 3-D printing methods and inexpensive materials to control the liquid metal, resulting in a compact device with frequency tunability from 3.4 to 2.35 GHz. The fabricated resonator sensor had a resonant amplitude and quality factor of −24 dB and 70, respectively – with less than 10% variation along the entire frequency tuning process. Experimental analysis of the sensor showed continuous variation as the volume of liquid metal was increased within the straight channel, with a consistent resonant frequency sensitivity to liquid metal of 375 MHz/cm. The device enables measurement of a microwave frequency spectrum with user-desired resolution. [ABSTRACT FROM AUTHOR]

A micro electrical discharge machining (μEDM) method that utilizes liquid phase alloy as the processing electrode is proposed and developed to solve various issues arising from electrode wear. The liquid alloy is held in a microcapillary needle such that a liquid microelectrode forms at the bottom of the needle. A discharge pulse generator is connected to the liquid and a workpiece for generating pulses thermally erodes the workpiece material. During the machining process, the liquid electrode is continuously supplied to the needle to eliminate effects of liquid consumption on the erosion process. Experimental results show that discharge pulses can be stably generated and sustained with the liquid electrode and that these pulses generated on the silicon sample are effective in implementing microcavities on its surface. Coating an electrically passivated material on the needle will protect the needle tip from the thermal action of the pulse discharge. The process is also evaluated under various experimental conditions for revealing the dependence of the material removal rate (MRR) and liquid alloy consumption rate (LACR) on the parameters. [ABSTRACT FROM AUTHOR]

This letter presents a new tuning method for coaxial cavity resonator-based bandpass filters (BPFs). The proposed tuning mechanism lays its foundations on pneumatically-actuated Galinstan that functionalizes the inner conductor of a capacitively-loaded coaxial cavity resonator. By altering the volume of Galinstan (i.e., height of inner conductor), ultrawide (>octave) and low loss RF tuning can be obtained without the need for small capacitive gaps that typically limit the RF performance of coaxial BPFs. To validate the concept, a coaxial cavity resonator with frequency tuning between 2.9 and 9.9 GHz (3.4:1 tuning range), and unloaded quality factor between 120 and 625 was manufactured and measured. Furthermore, the RF performance of a two-pole BPF with: 1) tunable frequency between 3.4 and 7.5 GHz (2.2:1); 2) an intrinsically switched-off state; 3) insertion loss <1 dB; and 4) return loss <10.5 dB was experimentally validated. [ABSTRACT FROM AUTHOR]

We investigated characteristics of highly flexible and stretchable electrodes consisting of Galinstan (i.e., a gallium-based liquid metal alloy) under various conditions including sub-zero temperature (i.e., 6 S m−1, which were still electrically conductive even if the stretching ratio increased up to 130% below 0 °C. In addition, the surface oxide (i.e., Ga2O3) layers possessing photo-responsive properties were spontaneously formed on the Galinstan surfaces under ambient conditions, which could be solely exfoliated using elastomeric stamps. By combining Galinstan and its surface oxide layers, solar-blind photodetectors were successfully fabricated on flexible substrates, exhibiting a distinct increase of up to 14.7% in output current under deep ultraviolet irradiation (254 nm wavelength) with an extremely low light intensity of 0.1 mW cm−2, whereas no significant change was observed under visible light irradiation.

In this article, the multimaterial extrusion (M-MEX) technology is used to fabricate, in a single step, a three-dimensional printed soft electromagnetic (EM) actuator, based on internal channels, filled with soft liquid metal (Galinstan) and equipped with an embedded strain gauge, for the first time. At the state of the art, M-MEX techniques result underexploited for the manufacture of soft EM actuators: only traditional manufacturing approaches are used, resulting in many assembly steps. The main features of this work are as follows: (1) one shot fabrication, (2) smart structure equipped with sensor unit, and (3) scalability. The actuator was tested in conjunction with a commercial magnet, showing a bending angle of 22.4° (when activated at 4A), a relative error of 0.7%, and a very high sensor sensitivity of 49.7 Two more examples, showing all the potentialities of the proposed approach, are presented: a jumping frog-inspired soft robot and a dual independent two-finger actuator. This article aims to push the role of extrusion-based additive manufacturing for the fabrication of EM soft robots: several advantages such as portability, no cooling systems, fast responses, and noise reduction can be achieved by exploiting the proposed actuation system compared to the traditional and widespread actuation mechanisms (shape memory polymers, shape memory alloys, pneumatic actuation, and cable-driven actuation)., Competing Interests: The authors declare no conflicts of interest., (Copyright 2023, Mary Ann Liebert, Inc., publishers.)

This paper reported a study on a flexible liquid metal coil (LMC) for electromagnetic collection from the transmission line for self-powered sensor and electromagnetic generation for wireless charging of cellular telephone. The room temperature liquid metal of Galinstan was perfused to elastic silicone tube, which is then terminated with gallium-plated copper wire. The as-prepared liquid metal wire can sustain stretching, twisting, and bending with large deformation, and has a good electrical contact stability with the external circuit. The LMC based magnetic energy harvester was then designed and demonstrated to collect the magnetic field energy induced by a wire carrying alternating current. The power of 260 mW was obtained for the wire carrying current of 10 A. The flexible toroidal inductor was fabricated and tested for magnetic energy harvesting. The flexible spiral-shaped LMC was also designed and demonstrated to power cellular telephone through wireless charging. The present study opens the way for further applications of elastic LMC in electromagnetic energy harvesting and charging. [ABSTRACT FROM AUTHOR]

Galinstan is a liquid metal based on gallium alloys consisting of gallium, indium and tin at a ratio of 67.5:22.5:10 by weight. It has been received great attention recently since it is fluidic and conductive at room temperature, even safe to humans. By utilizing a fringe capacitance of liquid galinstan, a pressure sensor and an object approach detecting sensor were fabricated. In a pressure sensor, the capacitance increases as the pressure increases and also the performance of the device is reversible by using an elastic PDMS substrate. In an object detecting approach sensor, the device can detect an approach of the grounded object by using fringe capacitance of liquid galinstan droplet and the performance of the device is also reversible. [ABSTRACT FROM AUTHOR]

Highlights • A practical galinstan based minichannel cooling system was developed, which can dissipate heat 300 W/cm2 and 1500 W. • The thermal performance and hydrodynamic characteristic of galinstan based minichannel heat sink was evaluated. • The heat capacity thermal resistance was an important factor for galinstan based minichannel cooling. • The pressure losses of galinstan minichannel heat sink was far lower than the water microchannel heat sink. • This cooling system can operate silently, steadily and smoothly. Abstract This paper is dedicated to experimentally investigate the liquid galinstan based minichannel cooling for high heat flux and large heat power thermal management. Firstly, a compact electromagnetic pump towards effectively driving liquid metals was developed, which can provide high pressure head up to 100 kPa. Then, the minichannel heat sink was designed and manufactured, with width of channel 1 mm, height of channel 5 mm. Furthermore, the galinstan based minichannel cooling system was established and experimentally tested under different heating loads and pumping powers. The results show that galinstan based minichannel cooling system can dissipate heat with heat flux 300 W/cm2 and heat power 1500 W. And the thermal performance and hydrodynamic characteristic of minichannel heat sink using galinstan as coolant were obtained. It indicates that compared to water based minichannel cooling, galinstan based minichannel cooling can obtain a rather larger heat transfer enhancement, and the pressure losses of galistan based minichannel heat sink is much lower than that of water based microchannel cooling. Moreover, it is also found that heat capacity thermal resistance becomes a rather important factor for the thermal performance of galinstan based minichannel, due to the high thermal conductivity and lower heat capacity of galinstan. Furthermore, the galinstan based minichannel cooling system can operate silently, steadily and smoothly by using electromagnetic pump, which has no moving parts. Overall, the galinstan based minichannel cooling is proven to be a powerful and practical way for the thermal management of high heat flux and large heat power devices. [ABSTRACT FROM AUTHOR]

This review is focused on the basic properties, production, functionalization, cytotoxicity, and biomedical applications of liquid metal nanoparticles (LMNPs), with a focus on particles of the size ranging from tens to hundreds of nanometers. Applications, including cancer therapy, medical imaging, and pathogen treatment are discussed. LMNPs share similar properties to other metals, such as photothermal conversion ability and a propensity to form surface oxides. Compared to many other metals, especially mercury, the cytotoxicity of gallium is low and is considered by many reports to be safe when applied in vivo. Recent advances in exploring different grafting molecules are reported herein, as surface functionalization is essential to enhance photothermal therapeutic effects of LMNPs or to facilitate drug delivery. This review also outlines properties of LMNPs that can be exploited in making medical imaging contrast agents, ion channel regulators, and anti-pathogenic agents. Finally, a foresight is offered, exemplifying underexplored knowledge and highlighting the research challenges faced by LMNP science and technology in expanding into applications potentially yielding clinical advances.