Eutectic Gallium-indium Alloy Research Articles

Liquid Metal-Based Flexible and Wearable Sensor for Functional Human-Machine Interface.

Rigid sensors are a mature type of sensor, but their poor deformation and flexibility limit their application range. The appearance and development of flexible sensors provide an opportunity to solve this problem. In this paper, a resistive flexible sensor utilizes gallium−based liquid metal (eutectic gallium indium alloy, EGaIn) and poly(dimethylsiloxane) (PDMS) and is fabricated using an injecting thin−line patterning technique based on soft lithography. Combining the scalable fabrication process and unique wire−shaped liquid metal design enables sensitive multifunctional measurement under stretching and bending loads. Furthermore, the flexible sensor is combined with the glove to demonstrate the application of the wearable sensor glove in the detection of finger joint angle and gesture control, which offers the ability of integration and multifunctional sensing of all−soft wearable physical microsystems for human–machine interfaces. It shows its application potential in medical rehabilitation, intelligent control, and so on.

Monolithically Programmed Stretchable Conductor by Laser-Induced Entanglement of Liquid Metal and Metallic Nanowire Backbone.

Owing to its low mechanical compliance, liquid metal is intrinsically suitable for stretchable electronics and future wearable devices. However, its invariable strain-resistance behavior according to the strain-induced geometrical deformation and the difficulty of circuit patterning limit the extensive use of liquid metal, especially for strain-insensitive wiring purposes. To overcome these limitations, herein, novel liquid-metal-based electrodes of fragmented eutectic gallium-indium alloy (EGaIn) and Ag nanowire (NW) backbone of which their entanglement is controlled by the laser-induced photothermal reaction to enable immediate and direct patterning of the stretchable electrode with spatially programmed strain-resistance characteristics are developed. The coexistence of fragmented EGaIn and AgNW backbone, that is, a biphasic metallic composite (BMC), primarily supports the uniform and durable formation of target layers on stretchable substrates. The laser-induced photothermal reaction not only promotes the adhesion between the BMC layer and substrates but also alters the structure of laser-irradiated BMC. By controlling the degree of entanglement between fragmented EGaIn and AgNW, the initial conductivity and local gauge factor are regulated and the electrode becomes effectively insensitive to applied strain. As the configuration developed in this study is compatible with both regimes of electrodes, it can open new routes for the rapid creation of complex stretchable circuitry through a single process.

Laser Writing of Eutectic Gallium–Indium Alloy Graphene‐Oxide Electrodes and Semitransparent Conductors (Adv. Mater. Technol. 5/2022)

Semitransparent and Conductive Electrodes In article number 2101238, Mahmoud Tavakoli and colleagues demonstrate that graphene oxide-coated liquid metal nanoparticles can be transformed to semitransparent and conductive electrodes, through a rapid, low-cost, and scalable laser processing technique. The authors used an infrared laser source for simultaneous laser sintering, thinning, and ablation of reduced graphene oxide coated eutectic gallium-indium alloy films, and demonstrated their application in fabrication of a high-resolution, semitransparent sensor for human breath monitoring.

An Antifatigue Liquid Metal Composite Electrode Ionic Polymer-Metal Composite Artificial Muscle with Excellent Electromechanical Properties.

Ionic polymer-metal composites (IPMC), one of the most popular materials in the field of artificial muscle research, have attracted much attention because of their high flexibility, low drive voltage (<10 V), high force density, large deformation, and so forth. However, the results show that the serious electrode fatigue crack and water loss of traditional IPMC greatly decrease its fatigue life and limit the practical application. In this study, we developed a novel liquid metal composite electrode. A layer of eutectic gallium-indium alloy (EGaIn) liquid metal was applied to the surface of the platinum electrode of the IPMC using a mask. Because of the good self-healing performance of the liquid metal, it is expected to solve the above problems of resistance increase and water loss caused by cracks. It turns out that the prepared EGaIn/Pt-IPMC exhibits a driving force up to 120 mN and maximum fatigue life of about 25,000 s at a driving voltage of 3 V. Compared with the best work reported, the fatigue strength of EGaIn/Pt-IPMC was increased by about 210%, and the maximum driving force of EGaIn/Pt-IPMC prepared by a single-layer basement membrane was between the IPMC prepared by 4-6 layer basement membrane. The electromechanical properties were significantly improved, and it is expected to realize a series of bionic applications.

Liquid metal-tailored gluten network for protein-based e-skin

Designing electronic skin (e-skin) with proteins is a critical way to endow e-skin with biocompatibility, but engineering protein structures to achieve controllable mechanical properties and self-healing ability remains a challenge. Here, we develop a hybrid gluten network through the incorporation of a eutectic gallium indium alloy (EGaIn) to design a self-healable e-skin with improved mechanical properties. The intrinsic reversible disulfide bond/sulfhydryl group reconfiguration of gluten networks is explored as a driving force to introduce EGaIn as a chemical cross-linker, thus inducing secondary structure rearrangement of gluten to form additional β-sheets as physical cross-linkers. Remarkably, the obtained gluten-based material is self-healing, achieves synthetic material-like stretchability (>1600%) and possesses the ability to promote skin cell proliferation. The final e-skin is biocompatible and biodegradable and can sense strain changes from human motions of different scales. The protein network microregulation method paves the way for future skin-like protein-based e-skin.

DC electric field-driven heartbeat phenomenon of gallium-based liquid metal on a floating electrode.

The heart beating phenomenon of room temperature liquid metal (LM) mercury has attracted much attention in the past years, but its research and application are limited because of the low vapor pressure and high toxicity. Here, a fundamental scientific finding is reported that the non-toxic eutectic gallium indium (EGaIn) alloy droplets beat periodically at a certain frequency based on a floating electrode under the stimulation of the direct current (DC) field. The essential characteristics of heart beating are the displacement and the projected area change of the LM droplet. The mechanism of this phenomenon is the self-regulation of interfacial tension caused by chemical oxidation, chemical corrosion, and continuous electrowetting. In this article, a series of experiments are also carried out to examine the effects of different factors on the heartbeat, such as voltage, the volume of the droplet, the droplet immersion depth, the electrolyte solution concentration, the distance of electrodes, and the type of floating electrode. Finally, the heartbeat state and application boundary of the LM droplet under different conditions are summarized by imitating the human life process. The periodic changes of the LM droplet under an external DC electric field provide a new method to simulate the beating of the heart artificially, and can be applied to the research of organ chip fluid pumping in the future.

Liquid metal polymer composite: Flexible, conductive, biocompatible, and antimicrobial scaffold

Gallium and its alloys, such as eutectic gallium indium alloy (EGaIn), a form of liquid metal, have recently attracted the attention of researchers due to their low toxicity and electrical and thermal conductivity for biomedical application. However, further research is required to harness EGaIn-composites advantages and address their application as a biomedical scaffold. In this research, EGaIn-polylactic acid/polycaprolactone composites with and without a second conductive filler, MXene, were prepared and characterized. The addition of MXene, into the EGaIn-composite, can improve the composite's electrochemical properties by connecting the liquid metal droplets resulting in electrically conductive continuous pathways within the polymeric matrix. The results showed that the composite with 50% EGaIn and 4% MXene, displayed optimal electrochemical properties and enhanced mechanical and radiopacity properties. Furthermore, the composite showed good biocompatibility, examined through interactions with fibroblast cells, and antibacterial properties against methicillin-resistant Staphylococcus aureus. Therefore, the liquid metal (EGaIn) polymer composite with MXene provides a first proof-of-concept engineering scaffold strategy with low toxicity, functional electrochemical properties, and promising antimicrobial properties.

Liquid-Metal-Assisted Deposition and Patterning of Molybdenum Dioxide at Low Temperature.

Molybdenum dioxide (MoO2), considering its near-metallic conductivity and surface plasmonic properties, is a great material for electronics, energy storage devices and biosensing. Yet to this day, room-temperature synthesis of large area MoO2, which allows deposition on arbitrary substrates, has remained a challenge. Due to their reactive interfaces and specific solubility conditions, gallium-based liquid metal alloys offer unique opportunities for synthesizing materials that can meet these challenges. Herein, a substrate-independent liquid metal-based method for the room temperature deposition and patterning of MoO2 is presented. By introducing a molybdate precursor to the surrounding of a eutectic gallium-indium alloy droplet, a uniform layer of hydrated molybdenum oxide (H2MoO3) is formed at the interface. This layer is then exfoliated and transferred onto a desired substrate. Utilizing the transferred H2MoO3 layer, a laser-writing technique is developed which selectively transforms this H2MoO3 into crystalline MoO2 and produces electrically conductive MoO2 patterns at room temperature. The electrical conductivity and plasmonic properties of the MoO2 are analyzed and demonstrated. The presented metal oxide room-temperature deposition and patterning method can find many applications in optoelectronics, sensing, and energy industries.

Laser Writing of Eutectic Gallium–Indium Alloy Graphene‐Oxide Electrodes and Semitransparent Conductors

AbstractGraphene encapsulated liquid metal particles is a novel and promising class of biphasic composite, with application in the next generation of electronic devices. Here, rapid, low‐cost, and scalable fabrication of solution processed large area rGO@EGaIn electrodes is demonstrated. rGO@EGaIn solution is first deposited over the substrate through spray coating, and then processed through a low‐cost laser (master oscillator power amplifier (MOPA)). This allows simultaneous reduction, thinning, ablation, and high resolution patterning of the deposited films. Surprisingly, it is found that by adjusting the laser parameters, it is possible to make semitransparent conductors via laser thinning of the films. Scanning electronic microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS) spectroscopy confirm that although the rGO/EGaIn weight ratio is only ≈0.08, the composite has a considerably different microstructure compared to the eutectic gallium–indium alloy (EGaIn) particles alone. Graphene oxide (GO) protects the EGaIn from extreme morphology change under laser irradiation. Therefore, various “shades” of rGO@EGaIn can be fabricated in a single film. This allows development of large electrodes with complex geometries in a few seconds. The conductivity, transparency, and reduction of the laser processed films are characterized by several techniques and an example of application is demonstrated by laser patterning a highly sensitive breath‐monitoring sensor.

Polydopamine Shell as a Ga3+ Reservoir for Triggering Gallium-Indium Phase Separation in Eutectic Gallium-Indium Nanoalloys.

Low melting point eutectic systems, such as the eutectic gallium-indium (EGaIn) alloy, offer great potential in the domain of nanometallurgy; however, many of their interfacial behaviors remain to be explored. Here, a compositional change of EGaIn nanoalloys triggered by polydopamine (PDA) coating is demonstrated. Incorporating PDA on the surface of EGaIn nanoalloys renders core-shell nanostructures that accompany Ga-In phase separation within the nanoalloys. The PDA shell keeps depleting the Ga3+ from the EGaIn nanoalloys when the synthesis proceeds, leading to a Ga3+-coordinated PDA coating and a smaller nanoalloy. During this process, the eutectic nanoalloys turn into non-eutectic systems that ultimately result in the solidification of In when Ga is fully depleted. The reaction of Ga3+-coordinated PDA-coated nanoalloys with nitrogen dioxide gas is presented as an example for demonstrating the functionality of such hybrid composites. The concept of phase-separating systems, with polymeric reservoirs, may lead to tailored materials and can be explored on a variety of post-transition metals.

Liquid metal embrittlement and deformation induced martensite: The case of 316 L austenitic steel LME by liquid eutectic gallium-indium

The liquid metal embrittlement sensitivity of a low nickel 316 L austenitic steel has been studied with eutectic gallium indium alloy. The embrittlement case is firmly established with this steel and studied by X-Ray fractography and EBSD. Brittle to ductile recoveries were observed via a dedicated parametric study (varying cross-head speed and temperature). The return to ductility with temperature is strongly correlated with a significant reduction in plastically induced α’ phase change suggesting it is a requirement for LME. This implies a strategy focused on limiting deformation induced martensite to design LME resistant austenitic steels at low temperature.

Stencil printed liquid metal based micron-sized interconnects for stretchable electronics

Eutectic gallium indium (E-GaIn) alloy based liquid metal is considered to be a promising material for manufacturing interconnects in stretchable electronics based applications due to its high electrical conductivity and inherent mechanical deformability. The current work demonstrates an easy and single step method of fabricating micron-sized (the width of ~ 200 μm) highly conducting stretchable interconnects by stencil printing of E-GaIn on stretchable polydimethylsiloxane (PDMS) substrate. The obtained stretchable pattern showed excellent electrical and mechanical property by exhibiting a low average resistance value of ~ 6.5 O even at elongation up to 50%. Moreover, it showed superior stability against stretching cycles with just ± 0.12 Ω of variation in resistance. A commercial light emitting diode was mounted on the patterns and illuminated to describe the role of interconnects in a realistic circuit.

Universal Self-Healing Poly(dimethylsiloxane) Polymer Crosslinked Predominantly by Physical Entanglements.

Harsh conditions are inevitable for long-term use of self-healing polymers. However, the majority of reported self-healing materials cannot remain stable under harsh conditions due to the presence of vulnerable dynamic crosslinking sites. Herein, a universal self-healing poly(dimethylsiloxane) (PDMS) polymer is reported. In our design, the PDMS polymer chains are crosslinked predominantly through physical entanglements. Owing to the invulnerable nature of the entanglement junctions and high mobility of polymer chains, the as-synthesized polymer exhibits autonomous self-healing capabilities not only under ambient conditions but also in a variety of harsh environments, including aqueous solutions, organic solvents, and extreme conditions (strong acid/alkali, redox agents, freezing temperature). Moreover, this polymer can be easily integrated with a eutectic gallium-indium (EGaIn) alloy to achieve layer-by-layer self-healing electronic skin sensors, which realize the combination of excellent electrical conductivity, long-term sensing stability, and universal self-healing capability.

Programmable Soft-Matter Electronics.

The hydrogels of the polyelectrolytes polyethylenimine and poly(acrylic acid) are used to form a thin-layer interface on the gallium-indium eutectic alloy's surface. The proposed method of gradually increasing the applied voltage reveals the possibility of formation of electronic components: diode, capacitor, resistor, and memristor. The components can be changed to each other many times. A multilayer perceptron model with one hidden layer and 12 nodes allows identifying hydrogels' composition and automatically setting the desired architecture of electronic components. The design of electronic components makes it possible to easy-to-produce new electronic parts and programmable soft-matter electronics.

Pattern-Reconfigurable Yagi–Uda Antenna Based on Liquid Metal

A pattern-reconfigurable Yagi–Uda antenna based on liquid metal is presented. The antenna consists of a balun-fed active dipole and a pair of stretchable passive parasitic dipoles, which are implemented by eutectic gallium-indium (EGaIn) alloy embedded in microfluidic channels. The parasitic dipoles are driven at each end by two low-cost, three-dimensional printed media rods. Afterward, spinning the rods at different angles leads to varying degrees of stretching upon the stretchable dipoles. Note the length of passive parasitic dipoles is a vital factor for antenna radiation reconfiguration. The antenna exhibits bidirectional radiation if the parasitic dipoles are equal in length. Otherwise, directional radiation toward the shorter parasitic dipole direction can be obtained. Based on the above-mentioned working principle, a pattern-reconfigurable antenna working in wireless local area network (WLAN) band is fabricated and measured. Apart from the reconfigurable capability, the proposed antenna keeps operating in the WLAN band of 2.4–2.48 GHz during the whole shape deformation.

Efficient and Stable Perovskite‐Based Photocathode for Photoelectrochemical Hydrogen Production

AbstractAlthough organometal halide perovskites (OHPs) have desirable photovoltaic properties, their photoelectrochemical (PEC) water‐splitting application for hydrogen production is limited by the instability originating from their intrinsic ionic defects and hygroscopic vulnerability. Herein, a highly efficient and stable OHP‐based photocathode achieved by a new zwitterion (L‐proline) passivation and a eutectic gallium indium alloy (EGaIn) encapsulation method is described. The zwitterion, which has both cations and anions, can simultaneously passivate both positively and negatively charged defects in OHPs. The resulting OHP photovoltaic cells with passivated shows an over 20% power conversion efficiency with an open‐circuit voltage of 1.13 V and a short‐circuit current of 22.13 mA cm−2. The EGaIn‐incorporated Ti foil provides complete encapsulation from the external environment while maintaining good transport of photogenerated charges from OHPs. Thus, these photocathodes exhibit a remarkable average photocurrent density of 21.2 mA cm−2 which has less than 5% current loss between PV cells and PEC cells. More admirably, the photocathode has the highest stability over 54 hours under continuous full sunlight illumination in a sulfuric acid electrolyte.

4D-Printable Liquid Metal-Liquid Crystal Elastomer Composites.

Soft actuators that undergo programmable shape change in response to a stimulus are enabling components of future soft robots and other soft machines. Strategies to power these actuators often require the incorporation of rigid, electrically conductive materials into the soft actuator, thus limiting the compliance and shape change of the material. In this study, we develop a 4D-printable composite composed of liquid crystal elastomer (LCE) matrix with dispersed droplets of eutectic gallium indium alloy (EGaIn). Using deformable EGaIn droplets in place of rigid conductive fillers preserves the compliance and shape-morphing properties of the LCE. The process enables 4D-printed LCE actuators capable of photothermal and electrothermal actuation. At low liquid metal (LM) concentrations (71 wt %), the composite actuator exhibits a photothermal response upon irradiation of near-IR light. Printed actuators with a twisted nematic configuration are capable of bending angles of 150° at 800 mW cm-2. At higher LM concentrations (88 wt %), the embedded LM droplets can form percolating networks that conduct electricity and enable electrical Joule heating of the LCE. Actuation strain ranging from 5 to 12% is controlled by the amount of electrical power that is delivered to the composite. We also introduce a method for multimaterial printing of monolithic structures where the LM filler loading is spatially varied. These multifunctional materials exhibit innate responsivity where the actuator behaves as an electrical switch and can report one of two states (on/off). These multiresponsive, 4D-printable composites enable multifunctional, mechanically active structures that can be powered with IR light or low DC voltages.

Reconfigurable Assembly of Active Liquid Metal Colloidal Cluster

AbstractWe report the reconfigurable assembly of rod‐shaped eutectic gallium–indium alloy (EGaIn) liquid metal colloidal motors by mimicking the growth behavior of a dandelion. EGaIn nanorods with a diameter of 210 nm and a length of 850 nm were synthesized via an ultrasound‐assisted physical dispersion method. The nanorods possess a core–shell structure with a 30 nm GaOOH shell and zero‐valent liquid core. The EGaIn motors move autonomously at a speed of 41.2 μm s−1 under an acoustic field. By modulating the frequency of the applied acoustic field, the EGaIn colloidal motors self‐organize into various striped and circular patterns, followed by a flower‐like cluster. The dandelion‐like EGaIn colloidal motor clusters move collectively and redisperse when the applied acoustic frequency is changed. Numerical simulations reveal that the flower‐like clusters are created by the acoustic propulsion in combination with steric repulsion and hydrodynamics.

Reconfigurable Assembly of Active Liquid Metal Colloidal Cluster.

We report the reconfigurable assembly of rod-shaped eutectic gallium-indium alloy (EGaIn) liquid metal colloidal motors by mimicking the growth behavior of a dandelion. EGaIn nanorods with a diameter of 210 nm and a length of 850 nm were synthesized via an ultrasound-assisted physical dispersion method. The nanorods possess a core-shell structure with a 30 nm GaOOH shell and zero-valent liquid core. The EGaIn motors move autonomously at a speed of 41.2 μm s-1 under an acoustic field. By modulating the frequency of the applied acoustic field, the EGaIn colloidal motors self-organize into various striped and circular patterns, followed by a flower-like cluster. The dandelion-like EGaIn colloidal motor clusters move collectively and redisperse when the applied acoustic frequency is changed. Numerical simulations reveal that the flower-like clusters are created by the acoustic propulsion in combination with steric repulsion and hydrodynamics.

All-Soft Supercapacitors Based on Liquid Metal Electrodes with Integrated Functionalized Carbon Nanotubes.

Soft energy storage devices, such as supercapacitors, are an essential component for powering integrated soft microsystems. However, conventional supercapacitors are mainly manufactured using hard/brittle materials that easily crack and eventually delaminate from the current collector by mechanical deformation. Therefore, to realize all-soft supercapacitors, the electrodes should be soft, stretchable, and highly conductive without compromising the electrochemical performance. This paper presents all-soft supercapacitors for integrated soft microsystems based on gallium-indium liquid metal (eutectic gallium-indium alloy, EGaIn) electrodes with integrated functionalized carbon nanotubes (CNTs). Oxygen functional groups on the surface of the CNTs ensure strong adhesion between the functionalized CNTs and the thin native oxide layer on the surface of EGaIn, which enables delamination-free soft and stretchable electrodes even under mechanical deformation. The electrochemical performances of fabricated all-soft supercapacitors in a parallel-plate arrangement were investigated without and with applied mechanical deformation. The fabricated supercapacitors exhibit areal capacitances as high as 12.4 mF cm-2 and show nearly unchanged performance under 30% applied strain.Theymaintain >95% of their original capacitance after >4200 charging and discharging cycles with a periodic applied strain of 30%. Finally, fabricated supercapacitors have been successfully integrated with a commercial light-emitting diode to demonstrate an integrated soft microsystem.