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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. Interfacial non-wettability between biocompatible iron oxide and liquid metal caused by the substantial mismatch in surface energy remains an issue. Here, the authors introduce a silver intermediate layer to reduce compositional mismatch and improve the wetting ability between iron oxide and liquid metal. [ABSTRACT FROM AUTHOR]

Printing or patterning particle‐based liquid metal (LM) ink is a good strategy to overcome poor wettability of LM for its circuits' preparation in flexible and printed electronics. Subsequently, a crucial step is to recover conductivity of LM circuits consisting of insulating LM micro/nano‐particles. However, most widely used mechanical sintering methods based on hard contact such as pressing, may not be able to contact the LM patterns' whole surface conformally, leading to insufficient sintering in some areas. Hard contact may also break delicate shapes of the printed patterns. Hereby, an ultrasonic‐assisted sintering strategy that can not only preserve original morphology of the LM circuits but also sinter circuits on various substrates of complex surface topography is proposed. The influencing factors of the ultrasonic sintering are investigated empirically and interpreted with theoretical understanding by simulation. LM circuits encapsulated inside soft elastomer are successfully sintered, proving feasibility in constructing stretchable or flexible electronics. By using water as energy transmission medium, remote sintering without any direct contact with substrate is achieved, which greatly protect LM circuits from mechanical damage. In virtue of such remote and non‐contact manipulation manner, the ultrasonic sintering strategy would greatly advance the fabrication and application scenarios of LM electronics. [ABSTRACT FROM AUTHOR]

The metallization of the SiC ceramic was realized with Sn0.5Zn at a relatively low temperature of 250 °C with the assistance of ultrasonication. This process avoided the use of high temperature, vacuum, or long holding time in traditional metallization methods. Results indicate that fine metallization without defects can be completed under ultrasonication excitation for 20 s. The bonding mechanism was forming a nano-scale layer of non-uniform but continuous amorphous zinc suboxide (ZnO 1-x) (even when the Zn was only 0.5 (wt%)), which acted as a transition region from the SiC ceramic substrate to the Sn0.5Zn metal layer. The tensile strength between the Sn0.5Zn layer and the SiC was 12.3 MPa. The acoustic pressure in the liquid Sn0.5Zn pool was calculated via COMSOL Multiphysics software. The simulation results show that alternating positive and negative acoustic pressure existed in the liquid Sn0.5Zn metal, with the highest amplitude of more than 107 Pa, thereby generating the cavitation effect. The collapse of cavitation bubbles resulted in micro-jets, hot spots, and a high cooling rate, promoting the movement of Zn atoms toward the SiC surface and the formation of ZnO 1-x. [ABSTRACT FROM AUTHOR]

Next‐generation electronics requiring high performance, recyclability, and low environmental impact are still in its infancy because of limited design strategies and materials. Herein, a facile approach for constructing liquid metal/wood anisotropic (LMWA) conductors via integration of gallium based LMs and delignified flexible wood (DF‐wood) is reported. Using a delignification treatment and a subsequent LM transfer process with patterns, a rigid and electrically insulating wood slice is converted into a flexible wood‐based LM conductor while retaining its original hierarchical porous structure. The LMWA conductor demonstrates a remarkable anisotropic electrical conductivity (σz/σx) on the order of 108. Subsequently, the LMWA conductors are successfully applied as flexible four‐channel tactile sensor, which exhibits excellent tactile sensitivity. Moreover, by immersing in a deep eutectic solvent (DES) composed of choline chloride with oxalic acid to dissolve the LM circuit, recycling of the LM is achieved with efficiency up to 96%. This is the first time that a DES is used to recycle LM, leading to increased economic and environmental viability of these sustainable electronics. The present LMWA conductors, which have the potential for a scalable and feasible fabrication process, substantially extend the scope of next‐generation electronics toward flexible and recyclable systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cavitation characteristics of Sn melt during ultrasonic-assisted spreading are studied through high-speed photography. • The bubble density decreases with the spreading of the droplet, which is correlated by acoustic pressure simulation. • A noncavitation region at spreading front is responsible for the phenomenon that the oxide layer is difficult to remove. • A method of measuring the cavitation threshold of liquid metals through experiment and numerical simulation is proposed. • The cavitation threshold of pure Sn is first identified, which is 1.26 MPa at 250 °C. The cavitation characteristics during the spreading of a pure Sn liquid droplet subjected to ultrasonication were studied for the first time through high-speed photography to reveal the wetting mechanism. Ultrasonic vibration realized the spreading of Sn droplet on the nonwetting pure Al substrate. However, the oxide layer of the substrate at the spreading front is difficult to remove. The high-speed photography result shows that a noncavitation region consistently appears at the spreading front, because the acoustic pressure is below the cavitation threshold of 1.26 MPa. In particular, the width of the noncavitation region gradually increases as the size of the spreading area increases. Such a result accounts for the condition wherein the oxide layer at the spreading front is difficult to remove. Furthermore, the bubble density during spreading gradually decreases due to the decreased acoustic pressure of the thinned liquid. Finally, the bubble dynamics were calculated to verify the wetting mechanism. [ABSTRACT FROM AUTHOR]

Rapidly homogenized joining has been a longstanding pursuit in the forming manufacturing of lightweight alloys structures. In this study, ultrasound energy was introduced into the joining process to accelerate cross-scale diffusion (direct grain migration rather than atomic-scale diffusion), and a homogeneous 6063Al joint was fabricated using a Zn-40Sn alloy at 360 °C in air. The network architecture joint composed entirely of α-Al grains was formed with a sandwich structure consisting of Sn@Al 2 O 3 /MgO as the grain boundary. The tensile strength of the joints was higher than that of the base metal in only a very short diffusion time (180 s). Physical effects of ultrasound in the Sn-Zn molten metal induced violent intergranular penetration, resulting in the decohesion and migration of the α-Al grains from the base metals and realizing a rapidly homogenized joining. This provides a foundation for full-strength joining of high-strength aluminum alloys with low thermal damage. [Display omitted] [ABSTRACT FROM AUTHOR]

• Thin liquid metal layer produces stronger cavitation with more uniform bubble size and distribution than bulk liquid. • Cavitation characteristics under different parameters are correlated with the acoustic pressure simulation results. • High acoustic pressure and strong cavitation can still be obtained at the weakly vibrated region. • High bubble growth speed of 16.8 m/s is obtained and evidenced by bubble dynamics calculation. Cavitation in thin layer of liquid metal has potential applications in chemical reaction, soldering, extraction, and therapeutic equipment. In this work, the cavitation characteristics and acoustic pressure of a thin liquid Ga–In alloy were studied by high speed photography, numerical simulation, and bubble dynamics calculation. A self-made ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and a max output power of 1000 W during the cavitation recording experiment. The pressure field characteristic inside the thin liquid layer and its influence on the intensity, types, dimensions, and life cycles of cavitation bubbles and on the cavitation evolution process against experimental parameters were systematically studied. The results showed that acoustic pressure inside the thin liquid layer presented alternating positive and negative characteristics within 1 acoustic period (T). Cavitation bubbles nucleated and grew during the negative-pressure stage and shrank and collapsed during the positive-pressure stage. A high bubble growth speed of 16.8 m/s was obtained and evidenced by bubble dynamics calculation. The maximum absolute pressure was obtained at the bottom of the thin liquid layer and resulted in the strongest cavitation. Cavitation was divided into violent and weak stages. The violent cavitation stage lasted several hundreds of acoustic periods and had higher bubble intensity than the weak cavitation stage. Cavitation cloud preferentially appeared during the violent cavitation stage and had a life of several acoustic periods. Tiny cavitation bubbles with life cycles shorter than 1 T dominated the cavitation field. High cavitation intensities were observed at high ultrasonication power and when Q235B alloy was used because such conditions lead to high amplitudes on the substrate and further high acoustic pressure inside the liquid. [ABSTRACT FROM AUTHOR]

Abstract: Power ultrasonic vibration (20kHz, 6μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air. [Copyright &y& Elsevier]