Showing papers on "Liquid metal published in 2022"

Rapid meniscus-guided printing of stable semi-solid-state liquid metal microgranular-particle for soft electronics

Abstract: Liquid metal is being regarded as a promising material for soft electronics owing to its distinct combination of high electrical conductivity comparable to that of metals and exceptional deformability derived from its liquid state. However, the applicability of liquid metal is still limited due to the difficulty in simultaneously achieving its mechanical stability and initial conductivity. Furthermore, reliable and rapid patterning of stable liquid metal directly on various soft substrates at high-resolution remains a formidable challenge. In this work, meniscus-guided printing of ink containing polyelectrolyte-attached liquid metal microgranular-particle in an aqueous solvent to generate semi-solid-state liquid metal is presented. Liquid metal microgranular-particle printed in the evaporative regime is mechanically stable, initially conductive, and patternable down to 50 μm on various substrates. Demonstrations of the ultrastretchable (~500% strain) electrical circuit, customized e-skin, and zero-waste ECG sensor validate the simplicity, versatility, and reliability of this manufacturing strategy, enabling broad utility in the development of advanced soft electronics.

Intermetallic wetting enabled high resolution liquid metal patterning for 3D and flexible electronics

Abstract: Liquid metals, highly conductive and flowable metals, are increasingly becoming versatile choices for soft electronics and wearable devices. High resolution liquid metal patterning strategies accommodative to different substrate materials and...

Liquid Metal Microgels for Three-Dimensional Printing of Smart Electronic Clothes.

Abstract: Gallium-based liquid metals (LMs), with the combination of liquid fluidity and metallic conductivity, are considered ideal conductive components for flexible electronics. However, huge surface tension and poor wettability seriously hinder the patterning of LMs and their wider applications. Herein, a recyclable liquid-metal-microgel (LMM) ink composed of LM droplets encapsulated into alginate microgel shells is proposed. During the mechanical stirring process, the released Ga3+ can cross-link with sodium alginate to form microgels covering the surface of LM droplets, which exhibits shear-thinning performance due to the formation and rupture of hydrogen bonds under different stress conditions, making the LMM ink possess excellent printability and superior adhesion to various substrates. Although patterns printed with the LMM ink are not initially conductive, they can be activated to recover conductivity by microstrain (<5%), pressing, and freezing. Additionally, the activated LMM circuit exhibits superior Joule heating behaviors and electrical performance in further investigation, including excellent conductivity, significant resistance response to strain with small hysteresis, great durability to nonplanar forces, and so forth. Furthermore, smart electronic clothes were fabricated and investigated by directly printing functional circuits on commercial clothes with the LMM ink, which integrate multiple functions, including tactile sensing, motion monitoring, human-computer interaction, and thermal management.

Biphasic Liquid Metal Composites for Sinter‐Free Printed Stretchable Electronics

Abstract: This work introduces and presents a comprehensive study on a series of biphasic liquid metal (LM) composites that benefit from high conductivity, excellent stretchability, a low gauge‐factor, excellent adhesion to a wide range of substrates, for sinter‐free writing complex stretchable circuits. These trinary material systems are composed of a block‐co‐polymer binder, EGaIn liquid metal, and a microparticle (μP) filler (Ag flakes, Ag‐coated‐Ni, Ag‐coated‐Fe, Ni, Ferrite, or TiC). They combine the fluidic behavior, resilience, and self‐healing properties of LMs, and the printability, adhesion, and elastic integrity of elastomers. Unlike the previous efforts with LM‐polymer composites and printed EGaIn nanodroplets, these composites are intrinsically conductive and do not require any thermal/optical/mechanical sintering. The binary combinations (LM‐SIS, LM‐Ag, Ag‐SIS) are first synthesized and characterized, and then the trinary LM‐μP‐SIS composites are evaluated. This includes analysis of microstructure, surface roughness, conductivity, electromechanical coupling, and LM smearing/leakage during mechanical loading, as well as the examination of the influence of filler particle size and composition. It is found that a binary combination of Ag‐EGaIn or EGaIn‐SIS does not result in the desired properties, and only trinary combination with conductive μP, preferably Ag, results in a printable, stretchable and sinter‐free composite. As an application, a digitally‐printed epidermal sticker for respiration monitoring is demonstrated.

Toxicity and Biocompatibility of Liquid Metals

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

Multifunctional liquid metal polymer composites

Abstract: Liquid metal polymer composites are an emerging class of functional materials with potentially transformative impacts in wearable electronics, soft robotics, and human-computer interactions. By employing different processing methods, room temperature liquid metal inclusions can be embedded in insulating polymers like elastomers to incorporate functional properties of metals while the matrix remains soft and stretchable. These solid–liquid composites offer an interesting, yet complex multifunctional material system. In this review, we present an exclusive overview of the synthesis methods, structural and functional properties, and applications of gallium-based liquid metal polymer composites. Common methods to control the size of liquid metal inclusions and their interaction in polymers are discussed. Moreover, the effect of liquid metal microstructures on the overall properties of the composites is summarized. We also highlight the new trends in terms of material composition, printing process, and novel applications of liquid metal polymer composites in intelligent systems.

Smart Eutectic Gallium–Indium: From Properties to Applications

Abstract: Eutectic gallium–indium (EGaIn), a liquid metal with a melting point close to or below room temperature, has attracted extensive attention in recent years due to its excellent properties such as fluidity, high conductivity, thermal conductivity, stretchability, self‐healing capability, biocompatibility, and recyclability. These features of EGaIn can be adjusted by changing the experimental condition, and various composite materials with extended properties can be further obtained by mixing EGaIn with other materials. In this review, not only the are unique properties of EGaIn introduced, but also the working principles for the EGaIn‐based devices are illustrated and the developments of EGaIn‐related techniques are summarized. The applications of EGaIn in various fields, such as flexible electronics (sensors, antennas, electronic circuits), molecular electronics (molecular memory, opto‐electronic switches, or reconfigurable junctions), energy catalysis (heat management, motors, generators, batteries), biomedical science (drug delivery, tumor therapy, bioimaging and neural interfaces) are reviewed. Finally, a critical discussion of the main challenges for the development of EGaIn‐based techniques are discussed, and the potential applications in new fields are prospected.

Imbibition-induced selective wetting of liquid metal

Abstract: Abstract Herein, we present the imbibition-induced, spontaneous, and selective wetting characteristics of gallium-based liquid metal alloys on a metallized surface with micro-scale topographical features. Gallium-based liquid metal alloys are fascinating materials that have enormous surface tension; therefore, they are difficult to pattern into films. The complete wetting of eutectic alloy of gallium and indium is realized on microstructured copper surfaces in the presence of HCl vapor, which removes the native oxide from the liquid metal alloy. This wetting is numerically explained based on the Wenzel’s model and imbibition process, revealing that the dimensions of the microstructures are critical for effective imbibition-driven wetting of the liquid metal. Further, we demonstrate that the spontaneous wetting of the liquid metal can be directed selectively along the microstructured region on the metallic surface to create patterns. This simple process enables the uniform coating and patterning of the liquid metal over large areas without an external force or complex processing. We demonstrate that the liquid metal-patterned substrates maintain electrical connection even in a stretched state and after repetitive stretching cycles.

Stretchable, sensitive, flexible strain sensor incorporated with patterned liquid metal on hydrogel for human motion monitoring and human-machine interaction

Abstract: Stretchable and biocompatible hydrogel-based strain sensors have considered as promising candidates for flexible wearable electronics in the light of their properties are similar to those of biological tissues. To date,...

Superelongation of Liquid Metal

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.

Liquid Metal Patterned Stretchable and Soft Capacitive Sensor with Enhanced Dielectric Property Enabled by Graphite Nanofiber Fillers

Abstract: In this work, we introduce liquid metal patterned stretchable and soft capacitive sensor with enhanced dielectric properties enabled by graphite nanofiber (GNF) fillers dispersed in polydimethylsiloxane (PDMS) substrate. We oxidized gallium-based liquid metal that exhibited excellent wetting behavior on the surface of the composites to enable patterning of the electrodes by a facile stencil printing. The fluidic behavior of the liquid metal electrode and modulated dielectric properties of the composite (k = 6.41 ± 0.092@6 wt % at 1 kHz) was utilized to fabricate stretchable and soft capacitive sensor with ability to distinguish various hand motions.

Conductive Polymer Enabled Biostable Liquid Metal Electrodes for Bioelectronic Applications

Abstract: Gallium (Ga)‐based liquid metal materials have emerged as a promising material platform for soft bioelectronics. Unfortunately, Ga has limited biostability and electrochemical performance under physiological conditions, which can hinder the implementation of its use in bioelectronic devices. Here, an effective conductive polymer deposition strategy on the liquid metal surface to improve the biostability and electrochemical performance of Ga‐based liquid metals for use under physiological conditions is demonstrated. The conductive polymer [poly(3,4‐ethylene dioxythiophene):tetrafluoroborate]‐modified liquid metal surface significantly outperforms the liquid metal.based electrode in mechanical, biological, and electrochemical studies. In vivo action potential recordings in behaving nonhuman primate and invertebrate models demonstrate the feasibility of using liquid metal electrodes for high‐performance neural recording applications. This is the first demonstration of single‐unit neural recording using Ga‐based liquid metal bioelectronic devices to date. The results determine that the electrochemical deposition of conductive polymer over liquid metal can improve the material properties of liquid metal electrodes for use under physiological conditions and open numerous design opportunities for next‐generation liquid metal‐based bioelectronics.

A Highly Stretchable and Permeable Liquid Metal Micromesh Conductor by Physical Deposition for Epidermal Electronics.

Abstract: Stretchable electronics allow functional devices to integrate with human skin seamlessly in an emerging wearable platform termed epidermal electronics. Compliant conductors represent key building components for functional devices. Among the various candidates, gallium-based liquid metals stand out with metallic conductivity and inherent deformability. Currently, the widespread applications of liquid metals in epidermal electronics are hindered by the low steam permeability and hence unpleasant wearing perceptions. In this study, a facile physical deposition approach is established to create a liquid metal micromesh over an elastomer sponge, which exhibits low sheet resistance (∼0.5 Ω sq-1), high stretchability (400% strain), and excellent durability. The porous micromesh shows textile-level permeability to achieve long-term wearing comfort. The conformal interaction of the liquid metal micromesh with the skin gives rise to a low contact impedance. An integrated epidermal sensing sleeve is demonstrated as a human-machine interface to distinguish different hand gestures by recording muscle contractions. The reported stretchable and permeable liquid metal conductor shows promising potentials in next-generation epidermal electronics.

Imbibition-induced selective wetting of liquid metal

Abstract: Abstract Herein, we present the imbibition-induced, spontaneous, and selective wetting characteristics of gallium-based liquid metal alloys on a metallized surface with micro-scale topographical features. Gallium-based liquid metal alloys are fascinating materials that have enormous surface tension; therefore, they are difficult to pattern into films. The complete wetting of eutectic alloy of gallium and indium is realized on microstructured copper surfaces in the presence of HCl vapor, which removes the native oxide from the liquid metal alloy. This wetting is numerically explained based on the Wenzel’s model and imbibition process, revealing that the dimensions of the microstructures are critical for effective imbibition-driven wetting of the liquid metal. Further, we demonstrate that the spontaneous wetting of the liquid metal can be directed selectively along the microstructured region on the metallic surface to create patterns. This simple process enables the uniform coating and patterning of the liquid metal over large areas without an external force or complex processing. We demonstrate that the liquid metal-patterned substrates maintain electrical connection even in a stretched state and after repetitive stretching cycles.

Liquid-Metal-Coated Magnetic Particles toward Writable, Nonwettable, Stretchable Circuit Boards, and Directly Assembled Liquid Metal-Elastomer Conductors.

Abstract: Liquid metal is a promising conductor material for producing soft and stretchable circuit "boards" that can enable next-generation electronics by electrically connecting and mechanically supporting electronic components. While liquid metal in general can be used to fabricate soft and stretchable circuits, magnetic liquid metal is appealing because it can be used for self-healing electronics and actuators by external magnetic fields. Liquid metal can be rendered into particles that can then be used for sensors and catalysts through sonication. We used this feature to produce "novel" conductive and magnetic particles. Mixing ferromagnetic iron particles into the liquid metal (gallium) produces conductive ferrofluids that can be rendered into gallium-coated iron particles by sonication. The gallium shell of the particles is extremely soft, while the rigid iron core can induce high friction in response to mechanical pressure; thus, hand-sintering of the particles can be used to directly write the conductive traces when the particles are cast as a film on elastic substrates. The surface topography of the particles can be manipulated by forming GaOOH crystals through sonication in DI water, thus resulting in nonwettable circuit boards. These gallium-coated iron particles dispersed in uncured elastomer can be assembled to form conductive microwires with the application of magnetic fields.

Transformable Gallium‐Based Liquid Metal Nanoparticles for Tumor Radiotherapy Sensitization

Abstract: The past decades have witnessed an increasing interest in the exploration of room temperature gallium‐based liquid metal (LM) in the field of microfluidics, soft robotics, electrobiology, and biomedicine. Herein, this study for the first time reports the utilization of nanosized gallium–indium eutectic alloys (EGaIn) as a radiosensitizer for enhancing tumor radiotherapy. The sodium alginate (Alg) functionalized EGaIn nanoparticles (denoted as EGaIn@Alg NPs) are prepared via a simple one‐step synthesis method. The coating of Alg not only prevents the aggregation and oxidation of EGaIn NPs in an aqueous solution but also enables them low cytotoxicity, good biocompatibility, and in‐situ formation of gels in the Ca2+ enriched tumor physiological microenvironment. Due to the metallic nature and high density, EGaIn can increase the generation of reactive oxygen species under the irradiation of X‐ray, which can not only directly promote DNA damage and cell apoptosis, but also show an efficient tumor inhibition rate in vivo. Moreover, EGaIn@Alg NPs hold good performance as computed tomography (CT) and photoacoustic tomography (PAT) imaging contrast agents. This work provides an alternative nanotechnology strategy for tumor radiosensitization and also enlarges the biomedical application of gallium‐based LM.

Control Mechanism of Particle Flow in the Weak Liquid Metal Flow Field on Non-Uniform Curvature Surface Based on Lippmann Model

Abstract: In order to realize the uniform distribution in the abrasive flow polishing of the titanium alloy workpiece with curved surface, a novel method based on the liquid metal-abrasive flow machining technology is proposed in this study. Based on the SST k-ω model, Preston model and fluid flow particle tracking model, the COMSOL software is employed to study the dynamic characteristics of liquid metal-abrasive flow under different AC electric field conditions, and the two-phase flow field is used to simulate the liquid state, the movement of liquid metal particles on the surface of the workpiece and the varitation of the Pv value in the near-wall region. It is found from numerical simulation results that the average Pv value in the strong flow field is 23,718.8 W/m2, and that in the weak flow field is 5,427.3 W/m2. By the assistance of the electric filed with the voltage of AC 36 V, the average Pv value of the liquid metal particles in the weak flow field is found to be 10,948.6 W/m2 with an increase of 101.7%. Therefore, to properly control the electric field strength, the movement of liquid metal in the flow field can be found to be controlled, and hence improving the uniformity of the turbulent kinetic energy on the workpiece surface and improving the processing quality.