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To quantify how the viscosities of silicone oil (SO) and liquid metal (LM) relate to emulsion-formation (LM-in-SO versus SO-in-LM), a process was developed to produce LM pastes with adjustable viscosity... 

Abstract Native oxides form on the surface of many metals. Here, using gallium‐based liquid metal alloys, Johnson‐Kendall‐Roberts (JKR) measurements are employed to show that native oxide dramatically lower the tension of the metal interface from 724 to 10 mN m⁻¹. Like conventional surfactants, the oxide has asymmetry between the composition of its internal and external interfaces. Yet, in comparison to conventional surfactants, oxides are an order of magnitude more effective at lowering tension and do not need to be added externally to the liquid (i.e., oxides form naturally on metals). This surfactant‐like asymmetry explains the adhesion of oxide‐coated metals to surfaces. The resulting low interfacial energy between the metal and the interior of the oxide helps stabilize non‐spherical liquid metal structures. In addition, at small enough macroscopic contact angles, the finite tension of the liquid within the oxide can drive fluid instabilities that are useful for separating the oxide from the metal to form oxide‐encased bubbles or deposit thin oxide films (1–5 nm) on surfaces. Since oxides form on many metals, this work can have implications for a wide range of metals and metal oxides in addition to explaining the physical behavior of liquid metal. 

Abstract Gallium-based liquid metals (LM) have surface tension an order of magnitude higher than water and break up into micro-droplets when mixed with other liquids. In contrast, silicone oil readily mixes into LM foams to create oil-in-LM emulsions with oil inclusions. Previously, the LM was foamed through rapid mixing in air for an extended duration (over 2 hours). This process first results in the internalization of oxide flakes that form at the air-liquid interface. Once a critical fraction of these randomly shaped solid flakes is reached, air bubbles internalize into the LM to create foams that can internalize secondary liquids. Here, we introduce an alternative oil-in-LM emulsion fabrication method that relies on the prior addition of SiO2 micro-particles into the LM before mixing it with the silicone oil. This particle-assisted emulsion formation process provides a higher control over the composition of the LM-particle mixture before oil addition, which we employ to systematically study the impact of particle characteristics and content on the emulsions' composition and properties. We demonstrate that the solid particle size (0.8 µm to 5 µm) and volume fraction (1% to 10%) have a negligible impact on the internalization of the oil inclusions. The inclusions are mostly spherical with diameters of 20 to 100 µm diameter and are internalized by forming new, rather than filling old, geometrical features. We also study the impact of the particle characteristics on the two key properties related to the functional application of the LM emulsions in the thermal management of microelectronics. In particular, we measure the impact of particles and silicone oil on the emulsion's thermal conductivity and its ability to prevent deleterious gallium-induced corrosion and embrittlement of contacting metal substrates. 

Abstract Liquid metals (LMs) have compelling applications in stretchable electronics, wearable devices, and soft robotics ascribing to the unique combination of room temperature fluidity and metallic electrical/thermal conductivity. Adding metallic elements in gallium‐based LMs can produce heterophasic (i.e., solid and liquid) LMs with altered properties including morphology, surface energy, rheology, electrical/thermal conductivity, and chemical reactivity. Importantly, heterophasic LMs can respond to external stimuli such as magnetic fields, temperature, and force. Thus, heterophasic LMs can broaden the potential applications of LMs. This report reviews the recent progress about heterophasic LMs through metallic elements in the periodic table and discusses their functionalities. The heterophasic LMs are systematically organized into four categories based on their features and applications including electrical/thermal conductivity, magnetic property, catalysis/energy management, and biomedical applications. This comprehensive review is aimed to help summarize the field and identify new opportunities for future studies.