Metals are excellent choices for electrical- and thermal-current conducting. However, either the stiffness of solid metals or the fluidity of liquid metals could be troublesome when flexibility and formability are both desired. To address this problem, a reliable two-stage route to improve the functionalities of gallium-based liquid metals is proposed. A series of stable semiliquid/semisolid gallium-based liquid metal amalgams with well-controlled particle packing ratios, which we call TransMixes, are prepared and characterized. Through effectively packing the liquid metal with copper particles (which are found to turn into intermetallic compound, CuGa, after dispersing), remarkable enhancements in electrical conductivity (6 × 10 S m, ∼80% increase) and thermal conductivity (50 W m K, ∼100% increase) are obtained, making the TransMixes stand out from current conductive soft materials. The TransMixes also exhibit appealing semiliquid/semisolid mechanical behaviors such as excellent adhesion, tunable formability, and self-healing ability. As a class of highly conductive yet editable metallic mixtures, the TransMixes demonstrate potential applications in fields like printed and/or flexible electronics and thermal interface materials, as well as other circumstances where the flexibility and conductivity of interfaces and connections are crucial.

Bulk liquid metals have prospective applications as soft and fluid electrical and thermal conductors in electronic and optical devices, composites, microfluidics, robotics, and metallurgy with unique opportunities for processing, chemistry, and function. Yet liquid metals' great potential in nanotechnology remains in its infancy. Although work to date focuses primarily on Ga, Hg, and their alloys, to expand the field, we define "liquid metals" as metals and alloys with melting points (mp) up to 330 °C, readily accessible and processable even using household kitchen appliances. Such a definition encompasses a family of metals including the majority of post-transition metals and Zn group elements (excluding Zn itself)with remarkable versatility in chemistry, physics, and engineering. These liquid alloys can create metallic compounds of different morphologies, compositions, and properties, thereby enabling control over nanoscale phenomena. In addition, the presence of electronic and ionic "pools" within the bulk of liquid metals, as well as deviation from classical metallurgy on the surfaces of liquid metals, provides opportunities for gaining new capabilities in nanotechnology. For example, the bulk and surfaces of liquid metals can be used as reaction media for creating and manipulating nanomaterials, promoting reactions, or controlling crystallization of dissolved species. Interestingly, liquid metals have enormous surface tensions, yet the tension can be tuned electrically over a wide range or modified via surface species, such as the native oxides. The ability to control the interfacial tension allows these liquids to be readily reduced in size to the nanoscale. The liquid nature of such nanoparticles enables shape-reconfigurable structures, the creation of soft metallic nanocomposites, and the dissolution or dispersion of other materials within (or on) the metal to produce multiphasic or heterostructure particles. This Perspective highlights the salient features of these materials and seeks to raise awareness of future opportunities to understand and to utilize liquid metals for nanotechnology.

Liquid metals offer unprecedented chemistry. Here it is shown that they can facilitate self-limiting oxidation processes on their surfaces, which enables the growth of metal oxides that are atomically thin. This claim is exemplified by creating atomically thin hydrated MnO 2 using a Galvanic replacement reaction between permanganate ions and a liquid gallium-indium alloy (EGaIn). The "liquid solution"-"liquid metal" process leads to the reduction of the permanganate ions, resulting in the formation of the oxide monolayer at the interface. It is presented that under mechanical agitation liquid metal droplets are established, and simultaneously, hydrated gallium oxides and manganese oxide sheets delaminate themselves from the interfacial boundaries. The produced nanosheets encapsulate a metallic core, which is found to consist of solid indium only, with the full migration of gallium out of the droplets. This process produces core/shell structures, where the shells are made of stacked atomically thin nanosheets. The obtained core/shell structures are found to be an efficient photocatalyst for the degradation of an organic dye under simulated solar irradiation. This study presents a new research direction toward the modification and functionalization of liquid metals through spontaneous interfacial redox reactions, which has implications for many applications beyond photocatalysis.

A biomimetic cellular‐eating phenomenon in gallium‐based liquid metal to realize particle internalization in full‐pH‐range solutions is reported. The effect, which is called liquid metal phagocytosis, represents a wet‐processing strategy to prepare various metallic liquid metal‐particle mixtures through introducing excitations such as an electrical polarization, a dissolving medium, or a sacrificial metal. A nonwetting‐to‐wetting transition resulting from surface transition and the reactive nature of the intermetallic wetting between the two metallic phases are found to be primarily responsible for such particle‐eating behavior. Theoretical study brings forward a physical picture to the problem, together with a generalized interpretation. The model developed here, which uses the macroscopic contact angle between the two metallic phases as a criterion to predict the particle internalization behavior, shows good consistency with experimental results.

Colloidal liquid metal alloys of gallium, with melting points below room temperature, are potential candidates for creating electrically conductive and flexible composites. However, inclusion of liquid metal micro‐ and nanodroplets into soft polymeric matrices requires a harsh auxiliary mechanical pressing to rupture the droplets to establish continuous pathways for high electrical conductivity. However, such a destructive strategy reduces the integrity of the composites. Here, this problem is solved by incorporating small loading of nonfunctionalized graphene flakes into the composites. The flakes introduce cavities that are filled with liquid metal after only relatively mild press‐rolling (<0.1 MPa) to form electrically conductive continuous pathways within the polymeric matrix, while maintaining the integrity and flexibility of the composites. The composites are characterized to show that even very low graphene loadings (≈0.6 wt%) can achieve high electrical conductivity. The electrical conductance remains nearly constant, with changes less than 0.5%, even under a relatively high applied pressure of >30 kPa. The composites are used for forming flexible electrically‐conductive tracks in electronic circuits with a self‐healing property. The demonstrated application of co‐fillers, together with liquid metal droplets, can be used for establishing electrically‐conductive printable‐composite tracks for future large‐area flexible electronics.

As a class of emerging multifunctional soft materials, gallium-based liquid metal (LM) amalgams, metal/nonmetal particles dispersed in an LM environment, suggest a combination of intriguing properties. In this article, Mg particles in gallium-indium alloy for making new conceptual biomedical materials, which can adapt to any irregular skin surface, are introduced, and superior photothermal effect with a 61.5% photothermal conversion (PTC) increase with respect to that of the LM is realized. The formation of a new intermetallic phase Mg Ga and adjustable surface roughness, which guarantees a rapid temperature increase when illuminated by laser, are found to be responsible for the photothermal effect enhancement. The obtained soft metallic mixtures also possess excellent thermal conductivity, favorable formability, together with benign biocompatibility. The potential use of the currently produced LM mixtures for conformable photothermal therapy (PTT) of skin tumors, which is hard to precisely heat otherwise via conventional ways, is explored. The soft Mg-GaIn mixtures can adapt to irregular tumor shapes to achieve conformable and minimal invasive tumor treatment. In vivo experiments on skin-tumor-bearing mice show obvious tumor growth suppression and life span extension after PTT treatment. As a novel functional PTC material, the Mg-GaIn mixtures exhibit promising potentials in the coming clinical cancer theranostics.

No abstract

No abstract