Liquid Metal Droplets Research Articles

Formation characteristics and acoustic regulation of liquid metal droplets in low-aspect-ratio channels

The uniformity in size of liquid metal droplets is crucial in determining the accuracy of flexible circuit printing as well as the stability in signal transmission. In this study, the numerical simulation and the experiment method are combined to analyze the droplet preparation process of liquid metal. Furthermore, the mechanism of the surface acoustic wave as an external force dominating the breakup of the liquid metal interface is investigated. The results show that the squeezing pressure and the capillary force are the dominant forces of the interface evolution in the low-aspect-ratio (height/width) channel. When the dispersed phase flow rate is low, the interface will retract upstream of the channel under the influence of large interfacial tension after breakup, resulting in fluctuations in flow rate, and therefore, the stability of droplet size is weak. When the dispersed phase flow rate is high, the interface randomly breaks up under the influence of the Rayleigh–Plateau instability, which also leads to uneven droplet size. As the acoustic intensity increases, the acoustic radiation pressure gradually becomes the dominant force responsible for the squeezing and breakup of the interface. It increases the radial contraction rate of the interface, shortens the droplet generation period, and ultimately reduces the droplet size. Additionally, the size deviation value is significantly reduced from 10.13% to 1.05%. This study is useful in elucidating the evolution mechanism of liquid metal interfaces in low-aspect-ratio channels, improving the fundamental theory of interface breakup caused by acoustic radiation pressure, and providing theoretical guidance for the controlled and stable production of liquid metal droplets.

Designing liquid metal microstructures through directed material extrusion additive manufacturing

Material extrusion (MEX) of soft, multifunctional composites consisting of liquid metal (LM) droplets can enable highly tailored properties for a range of applications from soft robotics to stretchable electronics. However, an understanding of how LM ink rheology and print process parameters can reconfigure LM droplet shape during MEX processing for in-situ control of properties and function is currently limited. Herein, the material (ink viscosity, and LM droplet size) and process (nozzle velocity, height from print bed, and extrusion rate) parameters are determined which control LM microstructure during MEX of these composites. The interplay and interdependence of these parameters is evaluated and nearly spherical LM droplets are transformed into highly elongated ellipsoidal shapes with an average aspect ratio of 12.4 by systematically tuning each individual parameter. Material and process relationships are established for the LM ink which show that an ink viscosity threshold should be fulfilled to program the LM microstructure from spherical to an ellipsoidal shape during MEX. Additionally, the thin oxide layer on the LM droplets is found to play a unique and critical role in the reconfiguration and retention of droplet shape. Finally, two quantitative design maps based on material and process parameters are presented to guide MEX additive manufacturing strategies for tuning liquid droplet architecture in LM-polymer inks. The insights gained from this study enable informed design of materials and manufacturing to control microstructure of emerging multifunctional soft composites.

Liquid Metal Powders Wrapped with Robust Shell by Bimetallic Ions Chelation Strategy for Energy Harvesting and Flexible Electronics

AbstractExcellent electrical and fluidic properties render liquid metal (LM) a promising material for flexible electronics, soft robotics, and stretchable circuits. Although producing LM micro/nano droplets by nanometerization addresses the tricky issue of the processing result from high surface tension, it still remains challenging to obtain stable LM droplets because of their dynamic surfaces. In this study, LM powders wrapped with robust shells are fabricated by bimetallic ions chelation strategy. During sonicating LM (e.g., EGaIn) in an alginate solution, a microgel shell is first formed by the coordination of Ga3+ and carboxyl groups. Subsequently, LM powders are achieved by introducing Ca2+ as secondary metal ions to chelate with redundant carboxyl groups. Besides high chemical stability in water and air, these nonstick LM powders also exhibit superior photothermal effects for energy harvesting, being capable of recovering electrical conductivity by mechanical sintering for flexible electronics. These conductive circuits based on LM powders not only work as electro‐thermal heaters, and electromagnetic interference shielding material but also can be designed as smart actuators. Thus, this bimetallic ions chelation strategy may start a pathway to produce stable, transportable LM powders with multifunctional properties, applicable in stretchable electronics, smart actuators, and electric skins.

Printing of liquid metal by laser-induced thermal bubble at the liquid–liquid interface

The dynamics of bubbles near a liquid–liquid interface represent a complex multiphase problem with numerous potential applications. This paper utilizes pulsed laser-induced microbubbles at the liquid–liquid interface to achieve the multi-orifice ejection of liquid metal microdroplets that are challenging to achieve with traditional inkjet printing. The study combines the expansion and collapse processes of thermal bubbles at the two-phase liquid interface with the ejection process of liquid metal droplets, unveiling the underlying mechanisms of liquid metal droplet ejection. In this work, the influence of laser parameters on the behavior of thermal bubbles at the liquid–liquid interface and the double-peak pressure effect was investigated. The impact of laser parameters on the ejection behavior of liquid metal droplets was also examined, which provides theoretical support for the wide applications of bubble dynamics at the liquid–liquid interface in the field of liquid metal inkjet printing.

Controlled generation of high-frequency liquid metal microdroplets

Liquid metal (LM) microdroplets with high conductivity and fluidity have drawn extensive attention in the field of electronics, biomedicine, and catalysis. The properties of LM droplets, e.g., melting points, electrical actuation, and stability, are affected by their sizes. Continuous generation of LM microdroplets with precisely controlled size will benefit their applications, which however, remains an outstanding challenge. In this study, we have designed a scalable high frequency droplet generator for the liquid metal (EGaIn) that works on the principle of manipulating the electrohydrodynamic behaviour of EGaIn. By applying electric potentials < − 0.75 V vs Ag/ AgCl, EGaIn droplets with uniform sizes can be rapidly and continuously generated. The electric potential effectively tunes the thickness of the oxide layer on the EGaIn surface which in turn modulates the surface tension of the EGaIn and induces the generation of consistent sized EGaIn droplets. The size of the EGaIn microdroplets can be varied between 40 and 200 µm, depending on the electric potential applied and the diameter of the exit orifice. Droplet generation using this method requires relatively low energies, i.e., 2.77 × 10-7 kWh, and is coupled with high frequency droplet generation ∼ 60 droplet/min. The scalability of this droplet generation methodology can be further increased via design of an array of exit orifice. With the presence of surfactants, these EGaIn droplets can remain well-dispersed without coalescing. This considerably widens their capability for further applications.

Anisotropy behavior of liquid metal elastomer composites with both enhanced thermal conductivity and crack resistance by direct ink writing

Liquid metal elastomer composites (LMEC) have broad application prospects in flexible devices, but the research on the basic processes of DIW for LMEC and the properties of DIW-ed LMEC is lacking. In this study, liquid metal (LM) is added to silicone elastomers such as Polydimethylsiloxane (PDMS), and the effect of LM volume fraction on ink rheology is investigated. Results show that the storage modulus of ink is lower than its loss modulus, which is not conducive to self-support formation. Therefore, fluorination is adopted to treat the silicon dioxide substrate used, thereby reducing the deformation rate of the printed structure to below 110 %. The results of properties show that the crack resistance and thermal conductivity of soft elastomers increase with the LM volume fraction. Additionally, the tensile properties of PDMS printed via DIW exhibit significant anisotropy parallel and perpendicular to the scanning direction, and that the addition of LM droplets reduces the anisotropy. And with the increase of curing temperature and LM droplet size, the stretchability of DIW-ed LMEC in both directions decreases, but only LMEC samples cured at 140 °C exhibit significant anisotropy. This study provides guidance pertaining to the basic process and printing directions for the application of DIW in the manufacture of LMEC equipment.

Cephalopod-inspired polymer composites with mechanically tunable infrared properties

Cephalopods have evolved an all-soft skin that can rapidly display colors for protection, predation, or communication. Development of synthetic analogs to mimic such color-changing abilities in the infrared (IR) region is pivotal to a variety of technologies ranging from soft robotics, flexible displays, dynamic thermoregulatory systems, to adaptive IR disguise platforms. However, the integration of tissue-like mechanical properties and rapid IR modulation ability into smart materials remains challenging. Here, by drawing inspiration from cephalopod skin, we develop an all-soft adaptive IR composite that can dynamically change its IR appearance upon equiaxial stretching. The biomimetic composite is built entirely from soft materials of liquid metal droplets and elastic elastomer, which are analogs of chromatophores and dermal layer of cephalopod skin, respectively. Driven by externally applied strains, the liquid metal inclusions transition between a contracted droplet state with corrugated surface and an expanded platelet state with relatively smooth surface, enabling dynamic variations in the IR reflectance/emissivity of the composite and ultimately resulting in reversible IR adaption. Strain-actuated flexible IR displays and pneumatically-driven soft devices that can dynamically manipulate their IR appearance are demonstrated as examples of the applicability of this material in emerging adaptive soft electronics.

3D Highly Stretchable Liquid Metal/Elastomer Composites with Strain‐Enhanced Conductivity

AbstractCurrent stretchable conductors, often composed of elastomeric composites infused with rigid conductive fillers, suffer from limited stretchability and durability, and declined conductivity with stretching. These limitations hinder their potential applications as essential components such as interconnects, sensors, and actuators in stretchable electronics and soft machines. In this context, an innovative elastomeric composite that incorporates a 3D network of liquid metal (LM), offering exceptional stretchability, durability, and conductivity, is introduced. The mechanics model elucidates how the interconnected 3DLM architecture imparts softness and stretchability to the composites, allowing them to withstand tensile strains of up to 500% without rupture. The relatively low surface‐to‐volume ratio of the 3DLM network limits the reforming of the oxide layer during cyclic stretch, thereby contributing to low permanent strain and enhanced durability. Additionally, the 3D architecture facilitates crack blunting and stress delocalization, elevating fracture resistance, while simultaneously establishing continuous conductive pathways that result in high conductivity. Notably, the conductivity of the 3DLM composite increases with strain during substantial stretching, highlighting its strain‐enhanced conductivity. In comparison to other LM‐based composites featuring 0D LM droplets, the 3DLM composite stands out with superior properties.

Super-tough, super-elastic, temperature-responsive, and tunable viscoelastic elastomer enabled by embedding nanosized liquid metal droplets

Liquid metal (LM) based composites are playing irreplaceable roles in many emerging fields such as stretchable and wearable electronics, soft robotics. However, it is still challenging to facilely fabricate the LM-based elastomers with nanosized and well-dispersed LM domains. Herein, the LM droplets filled elastomer nanocomposites (ENCs) with temperature-responsive, super-tough, super-elastic and tunable viscoelastic properties are introduced. By employing the conventional rubber processing method, LM is fragmented into nanoscale droplets and dispersed uniformly in cross-linked natural rubber (NR) without compromising the soft and highly stretchable properties of the matrix. In addition to the remarkable enhancement in tear resistance, the toughness of the resulting composites is strikingly improved as lowering the applied temperature, which is attributed to the phase transition and the simultaneous volume expansion of LM droplets. Surprisingly, for the viscoelasticity, this LM-based ENCs exhibit almost the same dynamic hysteresis with the pure NR system at the service condition of automobile tires, which is remarkably reduced compared to the traditional ENCs filled with rigid nanoparticles. Furthermore, this material also shows a good damping property for noise attenuation in the case of submarine covering. Collectively, this work opens a new avenue for the next generation of high-performance and multifunctional ENCs equipped in low-temperature working conditions.

Development of hierarchically constructed robust multifunctional hydrogels for sensitive strain sensors by using guar gum and polydopamine to encapsulate liquid metal droplets

Conductive hydrogels have aroused tremendous interest as strain sensing materials because of their good biocompatibility, high stretchability, and structural similarity to natural soft tissues. However, fabricating a multifunctional conductive hydrogel that simultaneously exhibits high toughness, high sensing performance and a low detection limit remains a challenge. Herein, we developed a new conductive hydrogel with a hierarchical cluster network structure by using soft Ga droplets encapsulated by guar gum (GG), in situ polymerized polydopamine (PDA) as conductive materials and in situ synthesized/Ga3+-crosslinked poly acrylic acid (PAA) as a ductile hydrogel matrix. GG and PDA around Ga droplets constituted physically crosslinked dense rigid networks. Because of its completely physically crosslinked hierarchical cluster network structure with Ga droplets, the hydrogel, which was named GG-PDA-Ga-PAA, exhibited high toughness (1.8 MJ/m3), good moldability, adhesiveness, antibacterial activity and excellent self-healing properties. Its conductivity recovered more than 90 % within 83 ms, while its tensile strength (213.2 kPa) and elongation at break (1364 %) recovered 92.8 % and 100 %, respectively, within 6 h. When applied as a strain sensing material, the GG-PDA-Ga-PAA hydrogel displayed high sensitivity (GF=10.83), short response/recovery time (167/167 ms), ultralow detection limit (0.2 %) and good fatigue resistance and cyclic stability (1000 cycles). Due to its excellent comprehensive properties, the hydrogel can be applied as a competent wearable stain sensor for monitoring various human activities from pulses in the radial artery to human joint bending. This work provides a new approach for producing multifunctional conductive hydrogels for strain sensors.

From Droplets to Devices: Recent Advances in Liquid Metal Droplet Enabled Electronics

AbstractLiquid metals, particularly non‐toxic gallium‐based alloys, have emerged as promising materials for future soft electronics due to their unique properties, including fluidity, excellent electrical and thermal conductivities, and surface reactivity. They demonstrate adaptability, responsivity, and self‐healing abilities, offering a platform for innovative electronic devices. Embodied in a droplet form factor, gallium‐based liquid metal droplets (LMDs) combine the traits of liquid metals with the advantages of miniaturized structures, including high surface tension, high surface area, high mobility, and surface functionalization. This review discusses the inherent properties of LMDs, which have driven substantial research interest across various fields, such as sensors, robotics, electronic circuits, energy harvesters, drug delivery, and microfluidics systems, among others. Effective fabrication and processing techniques are detailed for LMDs, illustrating their role in applications previously challenging with conventional materials, such as reconfigurable, self‐healing, and transient electronics. Existing challenges and future directions in this growing field are discussed. This extensive review seeks to further the understanding of LMDs and their potential, offering a roadmap for their journey from a niche interest to a key material in various electronic devices.

Sustainable epoxy composites with high thermal conductivity using poly(lipoic acid) modified liquid metal as crosslinkers

With the increasing demand for electronics integration and the increasing accumulation of e-waste, thermal management materials combing high conductivity and sustainability is highly desired. Herein, bio-based recyclable epoxy composites with significantly improved thermal conductivity were prepared by utilizing poly(lipoic acid) modified liquid metal (LM) as the crosslinkers. The strong interactions between poly(lipoic acid) and LM enable the formation of a poly(lipoic acid) shell layer coating on the LM droplet core, which facilitates the dispersion of LM droplets as well as interfacial thermal transport in the composites. As a result, the composite with only 25 vol% LM exhibits a thermal conductivity of 0.82 W/(m·K), which is higher than those of the previous studies with randomly filled LM at the same loading. In addition, attributed to the existence of dual dynamic bonds (disulfide bonds and β-hydroxyl ester bonds), the composites are reprocessable and their thermal conductivities are maintained after reprocessing. Moreover, the composites can be degraded under mild reducing conditions. This work presents a novel approach for the preparation of high-performance thermal management materials featuring recyclability and degradability.

Shock-induced atomisation of a liquid metal droplet

The present study uses Galinstan as a test fluid to investigate the shock-induced atomisation of a liquid metal droplet in a high-Weber-number regime $(We \sim 400\unicode{x2013}8000)$ . Atomisation dynamics is examined for three test environments: oxidizing (Galinstan–air), inert (Galinstan–nitrogen) and conventional fluids (deionised water–air). Due to the readily oxidizing nature of liquid metals, their atomisation in an industrial scale system is generally carried out in inert atmosphere conditions. However, no previous study has considered gas-induced secondary atomisation of liquid metals in inert conditions. Due to experimental challenges associated with molten metals, laboratory scale models are generally tested for conventional fluids like deionised water, liquid fuels, etc. The translation of results obtained from conventional fluid to liquid metal atomisation is rarely explored. Here a direct multiscale spatial and temporal comparison is provided between the atomisation dynamics of conventional fluid and liquid metals under oxidizing and inert conditions. The liquid metal droplet undergoes breakup through the shear-induced entrainment mode for the studied range of Weber number values. The prevailing mechanism is explained based on the relative dominance of droplet deformation and Kelvin–Helmholtz wave formation. The study provides quantitative and qualitative similarities for the three test cases and explains the differences in morphology of fragmenting secondary droplets in the oxidizing test case (Galinstan–air) due to rapid oxidation of the fragmenting ligaments. A phenomenological framework is postulated for predicting the morphology of secondary droplets. The formation of flake-like secondary droplets in the Galinstan air test case is based on the oxidation rate of liquid metals and the properties of the oxide layer formed on the atomizing ligament surface.

Machine learning (ML)-assisted surface tension and oscillation-induced elastic modulus studies of oxide-coated liquid metal (LM) alloys

Pendant drops of oxide-coated high-surface tension fluids frequently produce perturbed shapes that impede interfacial studies. Eutectic gallium indium or Galinstan are high-surface tension fluids coated with a ∼5 nm gallium oxide (Ga2O3) film and falls under this fluid classification, also known as liquid metals (LMs). The recent emergence of LM-based applications often cannot proceed without analyzing interfacial energetics in different environments. While numerous techniques are available in the literature for interfacial studies- pendant droplet-based analyses are the simplest. However, the perturbed shape of the pendant drops due to the presence of surface oxide has been ignored frequently as a source of error. Also, exploratory investigations of surface oxide leveraging oscillatory pendant droplets have remained untapped. We address both challenges and present two contributing novelties- (a) by utilizing the machine learning (ML) technique, we predict the approximate surface tension value of perturbed pendant droplets, (ii) by leveraging the oscillation-induced bubble tensiometry method, we study the dynamic elastic modulus of the oxide-coated LM droplets. We have created our dataset from LM’s pendant drop shape parameters and trained different models for comparison. We have achieved >99% accuracy with all models and added versatility to work with other fluids. The best-performing model was leveraged further to predict the approximate values of the nonaxisymmetric LM droplets. Then, we analyzed LM’s elastic and viscous moduli in air, harnessing oscillation-induced pendant droplets, which provides complementary opportunities for interfacial studies alternative to expensive rheometers. We believe it will enable more fundamental studies of the oxide layer on LM, leveraging both symmetric and perturbed droplets. Our study broadens the materials science horizon, where researchers from ML and artificial intelligence domains can work synergistically to solve more complex problems related to surface science, interfacial studies, and other studies relevant to LM-based systems.

Surface‐Engineered Liquid Metal Particles for Printing Stretchable Conductive Composites with Enhanced Stability Under Different Strain Rates

AbstractIntegrating liquid metal (LM) particles into compliant polymers presents an innovative approach for developing intelligent and adaptable systems in stretchable electronics, wearable devices, soft robotics, and other emerging technologies. However, the inherent electrically insulative nature of these solid‐liquid composites, compounded by the gallium oxide shell surrounding LM droplets, poses a significant challenge in establishing conductive pathways, especially for small droplet sizes and ultrasoft elastomers. Here, an interface modification approach that addresses this bottleneck and enables the synthesis of highly stretchable and printable composites with LM microparticles (&lt;2 µm) is presented. Polyvinylpyrrolidone (PVP) is used to functionalize these small LM inclusions, weakening the particle‐matrix interface, and facilitating the formation of a conductive percolating network under tensile strain. Optimized synthesis parameters result in printed conductive traces with excellent electrical conductivity (0.2 Ω cm−1), ultra‐high elongation at break (&gt;900% strain), and minimal resistance change (≈131%). Furthermore, this comprehensive study of the electromechanical response of these stretchable conductors under various strain rates reveals their exceptional stability under dynamic loading conditions, surpassing the performance of conductive traces composed of sprayed liquid metal. Finally, the potential application of these multifunctional materials in stretchable circuitry, addressing the demand for high stretchability and stability in wearable electronics, is demonstrated.

Top-down vs. bottom-up synthesis of Ga–based supported catalytically active liquid metal solutions (SCALMS) for the dehydrogenation of isobutane

Supported catalytically active liquid metal solutions (SCALMS) catalysts consist of a liquid metal solution of an active metal (e.g., Pd, Rh, Pt, Ni) in a low melting metal (e.g., Ga, In, Sn) deposited on a porous support material. In the current study, we extend and optimize the recently developed top-down synthesis protocol (ultrasonication of gallium metal) to prepare GaPd, GaRh and GaPt SCALMS systems. We compare the morphological differences in the obtained catalyst materials achieved between this approach and the more traditional bottom-up synthesis protocol (in situ thermal decomposition of triethylamino-gallane complex) using electron microscopy. Moreover, the spatial distribution of the catalytically active material in the porous alumina support is evaluated using high resolution argon physisorption measurements. Both techniques strongly indicate that the bottom-up approach leads to a high degree of pore penetration while the gallium droplets are largely on the outer surface in case of the top-down method. Changes to the surface chemistry of the support were also investigated by means of NH3/CO2 temperature programmed desorption. All catalytic systems synthesized by the two synthesis methods, i.e., GaPd, GaRh and GaPt, were tested in a quartz, fixed-bed tubular reactor for isobutane dehydrogenation. All SCALMS materials, irrespective of their individual synthesis protocol, were significantly more active than their pure metal counterparts. The SCALMS catalyst prepared using the bottom-up approach showed initial productivity of 407gbutenes molM–1 min−1, 832gbutenes molM–1 min−1, and 963gbutenes molM–1 min−1 for the GaPd, GaRh and GaPt respectively. These values represent more than twice the initial activity obtained with the top-down synthesized counterparts. This activity difference can be explained by the analytically determined difference in liquid metal droplet size distribution.

A stretchable, environmentally tolerant, and photoactive liquid metal/MXene hydrogel for high performance temperature monitoring, human motion detection and self-powered application

Conductive gels have received extensive attention in flexible electronics due to their diverse characteristics. The requirement for versatility and incompatibility of the conductive fillers with the hydrogel matrix remain a challenge for hydrogels. Herein, the cellulose nanofiber stabilized liquid metal droplets are utilized to initiate the polymerization and simultaneously serve as solid conductive fillers to construct the polyacrylamide/MXene/glycerol hydrogel with eligible stretchability (1000%) and high environmental adaptability (−25 to 80 °C) for multifunctional sensing. The hydrogel is utilized as a flexible electrode to construct the triboelectric nanogenerator for mechanical energy harvesting and conversion as well as self-powered sensing. Importantly, as a versatile sensor, it combines temperature sensing and deformation sensing with a wide range of stimulus responses and exceptional sensing performance. The flexible temperature and strain sensors are realized with superior thermosensitivity and strain sensitivity. In addition, the hydrogel exhibits favorable photothermal antibacterial ability. This work opens new avenues for the preparation of photothermal, conductive, stress and thermal sensitive hydrogels for multimodal sensors, sketching a promising future for them in flexible and wearable electronics.

Anti-leak, self-adaptive liquid metal-epoxy in-situ cured composites with ultra-low thermal resistance via flexible droplet inclusions

Generally, the function of thermal interface material (TIM) is filling rough surfaces, eradicating air pockets, decreasing thermal resistance, and improving heat dissipating effects. On this basis, we provide the TIM with another identity, “adhesion”, rendering it not only play a role of heat dissipation, but also serve as an adhesive to bond contacting surfaces. In this work, nano- to microscopic liquid metal (LM) droplets are embedded into the epoxy matrix to fabricate a LM-epoxy in-situ cured composite. By adding the curing agent, the LM-epoxy composite is cured into an entity structure, transforming from an amorphous grease state to a self-adaptive pad state. When the average droplet size is in a reasonable range of approximately 5–25 μm, the composite's thermal resistance (Rtotal) decreases to 2.19 mm2K/W at 70% volume fraction with its adhesive strength of 0.497 MPa, and the thermal conductivity (kTIM) could increase to 10.05 W/(m·K) at 85%. Both Rtotal and kTIM change rapidly for droplet size approximately ranging from 102 nm to 101 μm and then tend to level off when it further increases to 102 μm. A conception of equivalent contact thickness, δ, is presented to elucidate the contacting thermal resistance Rc, and set up predictive models of Rtotal for different volume fractions by considering the microscopic interfacial thermal resistance Rb between filler and matrix or not. This composite simultaneously possesses characteristics of the low thermal resistance like thermal grease, the whole entity like thermal pad, and the anti-leak characteristics by in-situ cured process. Actual cooling tests show it has a considerable temperature difference of 4.75 °C lower than the commercial thermal grease at 650 W heating power. This in-situ cured strategy, via decreasing the thermal resistance and solving the problem of LM leakage, remarkably promotes the LM-TIMs achieving a broader application prospect in the future.

Study on Flight Dynamics and Heat Transfer Solidification of Metal Droplets during Centrifugal Spray Deposition Forming Process

Centrifugal spray deposition forming technology, which is used in the preparation process of near-net-forming billets, not only reduces the macroscopic segregation and refines the microstructures of billets but also has the characteristics of a rapid solidification structure. The trajectory, velocity, heat transfer and solidification of metal droplets granulated by the centrifugal force during flight will affect the shape, precision and microstructure of the billet. Therefore, it is necessary to study the dynamics and thermal history of droplets in flight. In this study, a single droplet is taken as the object. Considering the resistance of ambient gas, Newton’s second law, classical nucleation theory, Newton’s cooling law and the energy conservation equation were used to establish a dynamic model and heat transfer solidification model of liquid metal droplets during flight. The influence of the centrifugal disc speed on the diameter of granulated droplets was analyzed. The variation law of droplet flight trajectory and velocity was explored. The supercooling degree in metal droplet nucleation was quantified, and the influence of droplet diameter, superheat and other factors on heat transfer and solidification was revealed. The results show that the numerical calculation results are basically consistent with the previous research results. The trajectory of the droplet is parabolic during flight. The initial velocity of the droplet, the environmental gas resistance and the convective heat transfer coefficient are positively correlated with the rotating speed of the centrifugal disc; however, the droplet diameter is negatively correlated with the rotating speed of the centrifugal disc. The super cooling degree at the time of droplet nucleation and the flight time required for solidification are negatively correlated with the droplet diameter. Among them, the droplet diameter has a linear relationship with the solidification start time and a quadratic curve relationship with the solidification end time. The effect of superheat on the heat transfer and solidification of droplets is not obvious. The conclusions obtained can provide a theoretical basis for the determination of the preparation process parameters.

Versatile Liquid Metal/Alginate Composite Fibers with Enhanced Flame Retardancy and Triboelectric Performance for Smart Wearable Textiles.

Liquid metal (LM) shows the superiority in smart wearable devices due to its biocompatibility and electromagnetic interference (EMI) shielding. However, LM based fibers that can achieve multifunctional integrated applications with biodegradability remain a daunting challenge. Herein, versatile LM based fibers are fabricated first by sonication in alginate solution to obtain LM micro/nano droplets and then wet-spinning into LM/alginate composite fibers. By mixing with high-concentration alginate solution (4-6wt.%), the LM micro/nano droplets stability (colloidal stability for > 30d and chemical stability for > 45d) are not only improved, but also facilitate its spinning into fibers through bimetallic ions (e.g., Ga3+ and Ca2+ ) chelation strategy. These resultant fibers can be woven into smart textiles with excellent flexibility, air permeability, water/salt resistance, and high temperature tolerance (-196-150°C). In addition, inhibition of smoldering result from the LM droplets and bimetallic ions is achieved to enhance flame retardancy. Furthermore, these fibers combine the exceptional properties of LM droplets (e.g., photo-thermal effect and EMI shielding) and alginate fibers (e.g., biocompatibility and biodegradability), applicable in wearable heating devices, wireless communication, and triboelectric nanogenerator, making it a promising candidate for flexible smart textiles.