Gallium based liquid metals (LM) have prospective biomedical, stretchable electronics, soft robotics, and energy storage applications, and are being widely adopted as thermal interface materials. The danger of gallium corroding...

Soft devices that sense touch are important for prosthetics, soft robotics, and electronic skins. One way to sense touch is to use a capacitor consisting of a soft dielectric layer sandwiched between two electrodes. Compressing the capacitor brings the electrodes closer together and thereby increases capacitance. Ideally, sensors of touch should have both large sensitivity and the ability to measure a wide range of stress (dynamic range). Although skin has such capabilities, it remains difficult to achieve both sensitivity and dynamic range in a single manmade sensor. Inspired by skin, this work reports a soft capacitive pressure sensor based on a bilayer of liquid metal elastomer foam (B‐LMEF). The B‐LMEF consists of an elastomer slab (elastic modulus: ≈655 kPa) laminated with a soft liquid metal elastomer foam (LMEF, elastic modulus: ≈7 kPa). The LMEF deforms at small stresses (<10 kPa), and both layers deform at large stresses (>10 kPa). The B‐LMEF has high sensitivity (0.073 kPa–1) at small stress and can operate over a large range of stress (200 kPa), which leads to a large dynamic range (≈4.1 × 105). Additionally, the elastomer slab has a large energy dissipation coefficient; the skin uses this property to cushion the human body from external stress and strain.

Gallium-based liquid metals (LMs) combine metallic properties with the deformability of a liquid, which makes them promising candidates for a variety of applications. To broaden the range of physical and chemical properties, a variety of solid additives have been incorporated into the LMs in the literature. In contrast, only a handful of secondary fluids have been incorporated into LMs to create foams (gas-in-LM) or emulsions (liquid-in-LM). LM foams readily form through mixing of LM in air, facilitated by the formation of a native oxide on the LM. In contrast, LM breaks up into microdroplets when mixed with a secondary liquid such as silicone oil. Stable silicone oil-in-LM emulsions form only during mixing of the oil with LM foam. In this work, we investigate the fundamental mechanism underlying this process. We describe two possible microscale mechanisms for emulsion formation: (1) oil replacing air in the foam or (2) oil creating additional features in the foam. The associated foam-to-emulsion density difference demonstrates that emulsions predominantly form through the addition of oxide-covered silicone oil capsules to the LM foam. We demonstrate this through density and surface wettability measurements and multiscale imaging of LM foam mixed with varied silicone oil contents in air or nitrogen environments. We also demonstrate the presence of a continuous silicone oil film on the emulsion surface and that this oil film prevents the embrittlement of contacting aluminum.

Conductive textiles are promising for human–machine interfaces and wearable electronics. A simple way to create conductive textiles by coating fabric with liquid metal (LM) particles is reported. The coating process involves dip‐coating the fabric into a suspension of LM particles at room temperature. Despite being coated uniformly after drying, the textiles remain electrically insulating due to the native oxide that forms on the LM particles. Yet, they can be rendered conductive by compressing the textile to rupture the oxide and thereby percolate the particles. Thus, compressing the textile with a patterned mold can pattern conductive circuits on the textile. The electrical conductivity of these circuits increases by coating more particles on the textile. Notably, the conductive patterns autonomously heal when cut by forming new conductive paths along the edge of the cut. The textiles prove to be useful as circuit interconnects, Joule heaters, and flexible electrodes to measure ECG signals. Further, the LM‐coated textiles provide antimicrobial protection against Pseudomonas aeruginosa and Staphylococcus aureus. Such simple coatings provide a route to convert otherwise insulating textiles into electrical circuits with the ability to autonomously heal and provide antimicrobial properties.

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