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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 Biosensors are analytical tools for monitoring various parameters related to living organisms, such as humans and plants. Liquid metals (LMs) have emerged as a promising new material for biosensing applications in recent years. LMs have attractive physical and chemical properties such as deformability, high thermal and electrical conductivity, low volatility, and low viscosity. LM‐based biosensors represent a new strategy in biosensing particularly for wearable and real‐time sensing. While early demonstrations of LM biosensors focus on monitoring physical parameters such as strain, motion, and temperature, recent examples show LM can be an excellent sensing material for biochemical and biomolecular detection as well. In this review, the recent progress of LM‐based biosensors for personalized healthcare and disease monitoring via both physical and biochemical signaling is survey. It is started with a brief introduction of the fundamentals of biosensors and LMs, followed by a discussion of different mechanisms by which LM can transduce biological or physiological signals. Next, it is reviewed example LM‐based biosensors that have been used in real biological systems, ranging from real‐time on‐skin physiological monitoring to target‐specific biochemical detection. Finally, the challenges and future directions of LM‐integrated biosensor platforms is discussed.