Mechanism behind the Controlled Generation of Liquid Metal Nanoparticles by Mechanical Agitation

The size-controlled synthesis of liquid metal nanoparticles is necessary in a variety of applications. Sonication is a common method for breaking down bulk liquid metals into small particles, yet the influence of critical factors such as liquid metal composition has remained elusive. Our study employs high-speed imaging to unravel the mechanism of liquid metal particle formation during mechanical agitation. Gallium-based liquid metals, with and without secondary metals of bismuth, indium, and tin, are analyzed to observe the effect of cavitation and surface eruption during sonication and particle release. The impact of the secondary metal inclusion is investigated on liquid metals' surface tension, solution turbidity, and size distribution of the generated particles. Our work evidences that there is an inverse relationship between the surface tension and the ability of liquid metals to be broken down by sonication. We show that even for 0.22 at. % of bismuth in gallium, the surface tension is significantly decreased from 558 to 417 mN/m (measured in Milli-Q water), resulting in an enhanced particle generation rate: 3.6 times increase in turbidity and ∼43% reduction in the size of particles for bismuth in gallium liquid alloy compared to liquid gallium for the same sonication duration. The effect of particles' size on the photocatalysis of the annealed particles is also presented to show the applicability of the process in a proof-of-concept demonstration. This work contributes to a broader understanding of the synthesis of nanoparticles, with controlled size and characteristics, via mechanical agitation of liquid metals for diverse applications.

Liquid metal synthesis solvents for metallic crystals

In nature, snowflake ice crystals arrange themselves into diverse symmetrical six-sided structures. We show an analogy of this when zinc (Zn) dissolves and crystallizes in liquid gallium (Ga). The low-melting-temperature Ga is used as a "metallic solvent" to synthesize a range of flake-like Zn crystals. We extract these metallic crystals from the liquid metal solvent by reducing its surface tension using a combination of electrocapillary modulation and vacuum filtration. The liquid metal-grown crystals feature high morphological diversity and persistent symmetry. The concept is expanded to other single and binary metal solutes and Ga-based solvents, with the growth mechanisms elucidated through ab initio simulation of interfacial stability. This strategy offers general routes for creating highly crystalline, shape-controlled metallic or multimetallic fine structures from liquid metal solvents.

Exploring Electrochemical Extrusion of Wires from Liquid Metals

Metal melt extrusion in gaseous or vacuum environments is a classical approach for forming wires. However, such extrusions have not been investigated in ionic solutions. Here, we use liquid metal (LM) gallium (Ga) and its eutectic alloy with indium (EGaIn) to explore the possibility of electrochemical extrusion of wires and study the tuning of the self-liming oxide layers as the coating for these wires formed during the process. By controlling the surface tension of the LM immersed in an electrolyte, and through the electrocapillary effect, we enable the extrusion of LM wires. The surface morphologies of LM wires and the thickness of the oxide layers are investigated when Ga and EGaIn are processed in neutral and basic electrolytes using various voltages. Taking advantage of the LM oxides, we show that LM wires offer tunable surface oxide thickness and composition using the electrochemical system and investigate the related working mechanisms. The wires are formed into patterns using an automated stage and show a self-healing capability. This work presents an unconventional method for electrochemical fabrication of LM wires, offering prospects for further research and industrial scale-up.

Liquid Metal-Based Route for Synthesizing and Tuning Gas-Sensing Elements

There is a strong demand for developing tunable and facile routes for synthesizing gas-sensitive semiconducting compounds. The concept of synthesizing micro- and nanoparticles of metallic compounds in a tunable process, which relies on liquid metals, is presented here. This is a liquid-based ultrasonication procedure within which additional metallic elements (In, Sn, and Zn) are incorporated into liquid Ga that is sonicated in a secondary solvent. We investigate liquid metal sonication in dimethyl sulfoxide (DMSO) and water to show their impact on the size, morphology, and crystal structure of the particulated products. The synthesized materials are annealed to investigate their responses to model reducing (H₂) and oxidizing (NO₂) gas species. The preparation process in DMSO gives rise to predominantly monoclinic Ga₂O₃ crystals which are favorable for gas sensing, while the emergence of rhombohedral Ga₂O₃ phases from the water sonication process led to inactive samples. The ease of tunability without hazardous precursors during the synthesis procedure is demonstrated. The route presented here can be uniquely employed for designing and engineering on-demand functional materials for sensing applications.

Advantages of eutectic alloys for creating catalysts in the realm of nanotechnology-enabled metallurgy

The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO₂ reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys.

The combination of metallurgy concepts and nanotechnology with liquid metal processing has been largely unexplored. Here the authors use liquid-phase ultrasonication to produce a model system of catalytically active nano-alloys, demonstrating electrocatalysis and photocatalysis.