Eutectic Gallium-indium Liquid Metal Research Articles

Multifunctional asymmetric foam with Compression-Enhanced EMI shielding effectiveness exhibits Real-Time tunability of Reflection/Absorption ratio and pressure sensing

Traditional electromagnetic interference (EMI) shielding materials usually have constant shielding effectiveness and fixed absorption/reflection ratio, and cannot respond to the real-time changing shielding requirements of smart wearable electronic devices. Herein, smart asymmetric foams (AF) composed of chromium dioxide decorated graphene (CrO2@G)/thermoplastic polyurethane-poly vinyl alcohol (TP) foams and a eutectic gallium-indium liquid metal (LM)/TP layer were developed via an efficient ‘split conductive modular design/assembly’ strategy. The AF with compressive stress-controlled conductivity can capture and attenuate electromagnetic (EM) waves in the form of absorption-dominated or reflection-dominated by adjusting the compressive strain in real time. The optimized AF achieved a low average reflection coefficient (R) of 0.12 and a minimum value of 0.05, holding the lowest record for LM-based EMI shielding materials with comparable SEt. As the compressive strain increases from 0 to 90 %, the AF alter its SEt from 63.8 ± 3 dB to 92.7 ± 2 dB, while reducing the average EM wave absorption efficiency from 88 % to 39 %, allowing it to be adjusted in real time as needed to block EM waves. Furthermore, the AF demonstrated its application as a strain sensor to monitor human motions. This work provides an effective strategy for the design and preparation of multifunctional smart EMI shielding materials.

Stabilizing Solid Electrolyte Interphase on Liquid Metal Via Dynamic Hydrogel-Derived Carbon Framework Encapsulation.

Eutectic gallium-indium liquid metal (EGaIn-LM), with a considerable capacity and unique self-healing properties derived from its intrinsic liquid nature, gains tremendous attention for lithium-ion batteries (LIBs) anode. However, the fluidity of the LM can trigger continuous consumption of the electrolyte, and its liquid-solid transition during the lithiation/de-lithiation process may result in the rupture of the solid electrolyte interface (SEI). Herein, LM is employed as an initiator to in situ assemble the 3D hydrogel for dynamically encapsulating itself; the LM nanoparticles can be homogeneously confined within the hydrogel-derived carbon framework (HDC) after calcination. Such design effectively alleviates the volume expansion of LM and facilitates electron transportation, resulting in a superior rate capability and long-term cyclability. Further, the "dual-layer" SEI structure and its key components, including the robust LiF outer layer and corrosion-resistant and ionic conductive LiGaOx inner layer are revealed, confirming the involvement of LM in the formation of SEI, as well as the important role of carbon framework in reducing interfacial side reactions and SEI decomposition. This work provides a distinct perspective for the formation, structural evolution, and composition of SEI at the liquid/solid interface, and demonstrates an effective strategy to construct a reliable matrix for stabilizing the SEI.

Deformable micro-supercapacitor fabricated via laser ablation patterning of Graphene/liquid metal

Deformable and miniaturized energy storage devices are essential for powering soft electronics. Herein, we fabricate deformable micro supercapacitors (MSCs) based on eutectic gallium-indium liquid metal (EGaIn) current collectors with integrated graphene. The well-define interdigitated electrode patterning with controlled gap is successfully realized by using the laser ablation because of a strong laser absorption of graphene and EGaIn. By judicious control of gap size between neighboring interdigitated electrodes and mass loading of graphene, we achieve a high areal capacitance (1336 µF cm−2) with reliable rate performance. In addition, owing to the intrinsic liquid characteristics of EGaIn current collector, the areal capacitance of fabricated MSC retains 90% of original value even after repetitive folding and 20% stretching up to 1000 cycles. Finally, we successfully integrate deformable MSC with a commercial light-emitting diode to demonstrate the feasibility of MSC as a deformable power source. The fabricated MSCs operate stably under various mechanical deformations, including stretching, folding, twisting, and wrinkling.

Flexible Finely and Directly Patternable Liquid Metal Electrodes via Selective Surface Wetting Technique

Eutectic gallium–indium (EGaIn) is an ideal material for preparing flexible electrodes, but its high surface tension poses a challenge during deposition and patterning. Herein, we propose a laser-induced selective surface wetting technique (SSWT) to enable the facile and straightforward fabrication of flexible finely and directly patternable EGaIn liquid metal electrodes. Our proposed technique selectively controls the wettability of EGaIn by establishing a perfluorinated self-assembled monolayer on a zinc oxide nanorod array to impart superhydrophobicity and then inducing specific sites on the hydrophilized surface by ultraviolet (UV) pulsed laser ablation, thereby enabling fine patterning (linewidth, ~50 μm). Surface analysis of the effect of laser ablation was also performed to elucidate the mechanism of SSWT. The patterned EGaIn liquid metal electrode fabricated by SSWT exhibited superior flexibility, with a resistance change (ΔR/R0) of only 18.6% compared with a Ag thin film electrode, which showed a dramatic increase in ΔR/R0 to nearly 500% after 50,000 folding cycles at a peak strain of 2.5%. The simple and easily implementable liquid metal patterning technique proposed in this study may potentially be applied in the field of wearable and stretchable electronics, which requires extreme flexibility.

Reactive wetting enabled anchoring of non-wettable iron oxide in liquid metal for miniature soft robot

Magnetic liquid metal (LM) soft robots attract considerable attentions because of distinctive immiscibility, deformability and maneuverability. However, conventional LM composites relying on alloying between LM and metallic magnetic powders suffer from diminished magnetism over time and potential safety risk upon leakage of metallic components. Herein, we report a strategy to composite inert and biocompatible iron oxide (Fe3O4) magnetic nanoparticles into eutectic gallium indium LM via reactive wetting mechanism. To address the intrinsic interfacial non-wettability between Fe3O4 and LM, a silver intermediate layer was introduced to fuse with indium component into AgxIny intermetallic compounds, facilitating the anchoring of Fe3O4 nanoparticles inside LM with improved magnetic stability. Subsequently, a miniature soft robot was constructed to perform various controllable deformation and locomotion behaviors under actuation of external magnetic field. Finally, practical feasibility of applying LM soft robot in an ex vivo porcine stomach was validated under in-situ monitoring by endoscope and X-ray imaging.

High‐Resolution 3D Deposition of Electrospun Fibers on Patterned Dielectric Elastomers

Electrostatic patterning has improved the performance of devices incorporating electrospun fibers in a wide variety of applications. However, the impact of process parameters on the final fiber pattern in these systems is rarely analyzed. Herein, a systematic analytical approach is developed to define quantitative metrics related to fiber patterning. Three‐dimensional patterned dielectric elastomer collectors are fabricated via solution‐casting polydimethylsiloxane with embedded carbon black or liquid metal droplets. Fiber patterning metrics are used to evaluate the effect of collector parameters such as insulating layer thickness, electrical ground surface area, and three‐dimensional pattern geometry. Dielectric layer parameters such as conductive material concentration and particle diameter are also investigated. Using this framework, the best‐performing collector is shown to improve selectivity 30‐fold, uniformity ninefold, reproducibility eightfold, and increase fiber volume by one order of magnitude. Furthermore, eutectic gallium indium liquid metal and scaled‐up pattern geometries demonstrate the tunability of this approach and broad applicability of systematic fiber pattern analysis. This rational approach to patterned fiber development can be applied to virtually any method or pattern to better understand the fiber patterning processes.

High-Precision Stretchable Ionic Temperature Sensor Passivated with a Liquid Metal/Block Copolymer Multilayer Film.

Moisture barriers are essential for ionic sensors because moisture has a direct impact on the stability and reliability of electrochemical properties. So far, stretchable moisture barriers that can maximize the advantage of using deformable ion gel as the active material have been rarely investigated and remain as a technological challenge. This study proposes a four-layer (4L) stretchable moisture barrier alternatively composed of a poly(styrene-isobutylene-styrene) copolymer (SiBS) film (2 μm in thickness) and a eutectic gallium-indium liquid metal (LM) film (1 μm in thickness). This multilayer barrier has a low water permeability of 9.09 × 10-20 m2/Pa s at 50% uniaxial strain (ε) and retains the barrier properties at repeated stretchable cycles at ε = 50%. This study demonstrates a skin-attached precise ion gel-based temperature sensor that is independent of moisture change (even dipping in water) and body motions.

Stable Organic Radical for Enhancing Metal-Monolayer-Semiconductor Junction Performance.

The preparation of monolayers based on an organic radical and its diamagnetic counterpart has been pursued on hydrogen-terminated silicon surfaces. The functional monolayers have been investigated as solid-state metal/monolayer/semiconductor (MmS) junctions showing a characteristic diode behavior which is tuned by the electronic characteristics of the organic molecule. The eutectic gallium-indium liquid metal is used as a top electrode to perform the transport measurements and the results clearly indicate that the SOMO-SUMO molecular orbitals impact the device performance. The junction incorporating the radical shows an almost two orders of magnitude higher rectification ratio (R(|J1V/J-1V|) = 104.04) in comparison with the nonradical one (R(|J1V/J-1V|) = 102.30). The high stability of the fabricated MmS allows the system to be interrogated under irradiation, evidencing that at the wavelength where the photon energy is close to the band gap of the radical there is a clear enhancement of the photoresponse. This is translated into an increase of the photosensitivity (Sph) value from 68.7 to 269.0 mA/W for the nonradical and radical based systems, respectively.

Highly efficient and eco-friendly InP-based quantum dot light-emitting diodes with a synergetic combination of a liquid metal cathode and size-controlled ZnO nanoparticles

Colloidal quantum dot light-emitting diodes (QLEDs) are the most promising candidates for next-generation displays due to wide color gamut, high contrast ratio, and narrow bandwidth emission. However, high-efficiency QLEDs based on toxic cadmium-based quantum dots (QDs) are strictly regulated by environmental law, and therefore environmentally friendly fabrication methods using non-cadmium-based QDs are indispensable for industrial applications. In this study, an eco-friendly and scalable fabrication strategy based on a synergetic combination of colloidal InP QDs, a eutectic gallium-indium liquid metal, and size-controlled ZnO nanoparticles was developed to produce highly efficient, environmentally friendly, solution-processable QLEDs. The cathode electrode of a gallium alloy liquid metal was applied using a simple screen-printing method, and the InP/GaP/ZnS green QDs with an excellent photoluminescence quantum yield of 85% were facilely prepared and incorporated into the device through spin coating process, ensuring that high device efficiency of InP-based QLED was achieved through uniform electroluminescence of active area. In addition, a size-controlled synthetic method for ZnO nanoparticles as the electron transfer layer was developed to improve the quantum efficiency of InP QDs, and consequently the optoelectronic performance of the resulting device was higher than that of conventional device in terms of current density, luminance, and external quantum efficiency.

Flexible liquid metal display using 3-Aminopropyl triethoxysilane-treated light emitting diodes (LEDs) array

In recent years, the fabrication of flexible electronic devices has been focused on the use eutectic gallium‑indium (EGaIn) liquid metal (LM) materials with polydimethylsiloxane (PDMS) microfluidics, which are less toxic. The flexible electronic devices offer the advantage of attaining various shapes as they are liquid at room temperature. However, discontinuities in the circuit occur while bending of the flexible LM circuit as EGaIn LM easily leaks into the space between the electrical components such as light-emitting diodes (LEDs) and PDMS microfluidic channels. Thus, the present study proposes use of a (3-Aminopropyl) triethoxysilane (APTES)-treatment method to create a circuit consisting of 100 μm channels based on EGaIn. The strategy enhances the bonding strength of surface mount device (SMD) such as LEDs and PDMS. The circuit mold to be patterned with the PDMS has been made with a 3D printer and coated with a polymer as buffer layer to allow the PDMS to detach the circuit mold easily. The change in resistance of the EGaIn LM by varying the bending angle from 0° to 60° is presented for one channel through the I-V curves. Additionally, effect of bending on the on/off state of an APTES-treated SMD type LED has been studied. Furthermore, the proposed method has been employed for developing a 5 × 1 LED array circuit. An Arduino has been employed to express a 5 × 5 LED array circuit in the form of letters. Hence, a flexible device with improved stability has been demonstrated using EGaIn LM that does not overflow while bending due to an enhanced binding force between the PDMS and SMD-type LEDs as a result of the APTES-treatment processing.

EGaIn coated 3D-Cu foam as a self-healing current collector for lithium ion batteries

Traditional lithium-ion batteries are prone to cracks and perforations in extreme environments, which could cause electrochemical performance degradation or even safety problems. Here, based on the alloying reaction of liquid metal, through the adjustment of alloying temperature and reaction time, a uniform and stable dispersion of eutectic gallium indium liquid metal (EGaIn) on the surface and internal structure of the micro-etched 3D-Cu current collector (EGaIn@3D-Cu) is obtained. Furthermore, the graphite anode prepared with the EGaIn@3D-Cu current collector (the self-healing graphite anode) shows an excellent self-healing performance. Namely, the specific capacities of the self-healing graphite anode before and after scratch damage are 327.4 mA h g−1 and 309.6 mA h g−1, respectively, which is significantly better than that of the graphite anode assembled with 2D-Cu foil current collector. Therefore, the EGaIn@3D-Cu current collector prepared by a simple manufacturing process could effectively realizes the self-healing function, prevent the capacity degradation and improve the stability of the battery.

Wearable eutectic gallium-indium liquid fuel cells

With the rapid growth of wearable electronics, the development of wearable fuel cells as a smart power source is receiving ever more attention due to their high energy conversion efficiency, modest operating temperature, and ease of handling. To address the most notable limiting factor, the rigid electrodes, of fuel cells, herein, a eutectic gallium-indium liquid metal with excellent deformability and redox ability has been employed to wearable and rechargeable fuel cells with high performance. Thanks to the optimized Ga/In ratio, which is achieved by balancing the anticorrosion and electrochemical activity of the liquid metal anode, the power density of the fuel cell is as high as 72.8 mW cm−2; to our knowledge, this is the highest power density among existing wearable liquid fuel cells at room temperature. Due to the stable redox properties of liquid metal, the fuel cell was stably cycled for 96 h at 2 mA cm−2 as a rechargeable metal-air battery. Meanwhile, running in feed mode to maintain the proportion of Ga in the anode, the fuel cell and the rechargeable liquid metal fuel cell exhibited stable discharging and cycling performances, respectively, and delivered exemplary performances under various flexibility and stretchability measurements. Based on the fluent and renewable liquid metal anode, this novel high-performance wearable liquid fuel cell shows great promise as a shape-variable energy supply for bionic soft robots and wearable devices.

Flexible Capacitive Pressure Sensor Based on PDMS Substrate and Ga–In Liquid Metal

A novel flexible pressure sensor, based on polydimethylsiloxane (PDMS) and eutectic gallium–indium (EGaIn) liquid metal, was developed for detecting various applied pressures. The sensor was fabricated with PDMS polymer-based electrode channels that are filled with EGaIn liquid metal. The liquid metal-based electrodes were designed to form four capacitors (C1, C2, C3, and C4). Conventional printed circuit board technology was used to manufacture the master mold to form the PDMS-based electrode channels. Corona discharge treatment was employed to bond the PDMS layers at room temperature, under atmospheric pressure. The capability of the fabricated pressure sensor was demonstrated by investigating the capacitive-based response of the device for varying applied pressures. Average capacitance changes ranging from 2.3% to 12.0%, 2.6% to 11.8%, 2.5% to 12.2%, and 2.7% to 13.1% when compared with the based capacitance of 14.1, 15.1, 13.8, and 13.3 pF were obtained for C1, C2, C3, and C4, respectively, for applied pressures ranging from 0.25 to 1.10 MPa. A linear relationship was obtained for the average capacitance change with a sensitivity of 0.11%/MPa and a correlation coefficient of 0.9975. The results obtained thus demonstrate the feasibility of employing liquid metal-based electrodes for the fabrication of flexible pressure sensing devices.

Fluorinated benzalkylsilane molecular rectifiers.

We report on the synthesis and electrical properties of nine new alkylated silane self-assembled monolayers (SAMs) – (EtO)3Si(CH2)nN = CHPhX where n = 3 or 11 and X = 4-CF3, 3,5-CF3, 3-F-4-CF3, 4-F, or 2,3,4,5,6-F, and explore their rectification behavior in relation to their molecular structure. The electrical properties of the films were examined in a metal/insulator/metal configuration, with a highly-doped silicon bottom contact and a eutectic gallium-indium liquid metal (EGaIn) top contact. The junctions exhibit high yields (>90%), a remarkable resistance to bias stress, and current rectification ratios (R) between 20 and 200 depending on the structure, degree of order, and internal dipole of each molecule. We found that the rectification ratio correlates positively with the strength of the molecular dipole moment and it is reduced with increasing molecular length.

수퍼커패시터 응용을 위한 EGaIn 액체 금속 전극의 전기화학 특성 연구

Abstract >> Recent years, supercapacitors have been attracting a growing attention as an efficient energy storage,due to their long-lifetime, device reliability, simple device structure and operation mechanism and, most importantly,high power density. Along with the increasing interest in flexible/stretchable electronics, the supercapacitors withcompatible mechanical properties have been also required. A eutectic gallium-indium (EGaIn) liquid metal couldbe a strong candidate as a soft electrode material of the supercapacitors because of its insulating surface oxidelayer for electric double layer formation. Here, we report the electrochemical study on the charging/reaction process at the interface of EGaIn liquid metal and electrolyte. Numerical fitting of the charging current curves provides the capacitance of EGaIn/insulating layer/electrolyte (~38 F/m 2 ). This value is two orders of magnitude higherthan a capacitance of a general metal electrode/electrolyte interface.Key words : Eutectic Gallium-indium liquid metal(갈륨-인듐 공융합금), Supercapacitor(수퍼커패시터), Oxide layer(산화막), Electrochemistry(전기화학), Electric double-layer(전기 이중층)

다이폴 상태와 루프 상태로 변환 가능한 종이접기 방식의 종이 안테나

본 논문에서는 잉크젯 프린팅 기술을 이용하여 종이 필름 위에 전도성 잉크를 인쇄하여 방사 패턴 변환이 가능한 종이접기 형태의 안테나를 제안한다. 제안된 안테나는 접었을 때와 펼쳤을 때 각각 다이폴 안테나와 루프 안테나로 동작하며, 종이 필름을 접고 펼치는 방식에 따라 상호 변환될 수 있다. 제안된 안테나는 다이폴 상태와 루프 상태일 때 모두 동일하게 1.85 GHz에서 동작하도록 설계되었다. 종이 필름을 접었을 때 종이 필름의 코팅과 그 위에 인쇄된 전도성 잉크가 깨짐 현상을 해결하기 위해 액체금속(liquid metal)중 하나인 EGaIn(Eutectic Gallium Indium)을 사용하였다. 제안된 안테나의 성능은 시뮬레이션과 실제 측정 결과로 확인할 수 있으며, 다이폴 상태와 루프 상태일 때 안테나 이득은 각각 -4 dBi, -5 dBi이다. 또한, 측정 결과, 다이폴 상태와 루프 상태일 때 서로의 Null 부분을 서로 상호 보완해 주는 것을 확인할 수 있다. A pattern-switchable origami antenna is designed with paper using inkjet-printing technology. The proposed antenna can be switched between loop and dipole antenna modes by folding and unfolding the paper, respectively. The proposed antenna is designed for the resonant frequencies of both modes to be 1.85 GHz. Eutectic gallium-indium liquid metal is introduced in order to avoid cracks in the conductive ink when the paper is folded. The performance of the proposed antenna is demonstrated through simulation and measurement results and antenna gain of dipole-mode and loop-mode are -4 dBi and -5 dBi, respectively. Also, the nulls of both dipole and loop modes compensate nulls from each mode.

A study of the production and reversible stability of EGaIn liquid metal microspheres using flow focusing

This manuscript describes an experimental study of the production of micro-scale droplets of the room-temperature liquid alloy eutectic gallium indium (EGaIn) formed using a microfluidic flow-focusing device. The EGaIn surface oxidizes readily to form a passivating oxide "skin" that imparts some mechanical stability to the resulting microspheres, but does not appear to affect the dynamics of droplet formation. EGaIn has an interfacial tension nearly an order of magnitude larger than typical water-in-oil systems that are used to study droplet production in microfluidic flow-focusing devices. The size of the microdroplets increase as the ratio of the flow rates of the dispersed and continuous-phase increase for both EGaIn-in-glycerol and water-in-oil systems; however, these fluid pairs form droplets through different dispersing modes at otherwise identical flow conditions (i.e., flow rate ratios and capillary numbers). Consequently, the EGaIn droplets are larger than the water droplets. The difference in dispersing modes and droplet size are attributed to the relatively larger interfacial and inertial forces of the EGaIn system compared to the water-in-oil system. The addition of polyvinyl alcohol (PVA), which is known to bind to oxide surfaces, to the continuous phase yields stable, monodisperse emulsions of liquid metal. These emulsions can be destabilized on demand by changing the solution pH, allowing the liquid metal to be recovered. The ability of the PVA to bind to the liquid metal also influences droplet production by changing the shape of the liquid as it approaches the orifice of the flow focusing device, which results in droplets with smaller diameters relative to those formed without PVA.