An official website of the United States government
Possessing a unique combination of properties that are traditionally contradictory in other natural or synthetical materials, Ga-based liquid metals (LMs) exhibit low mechanical stiffness and flowability like a liquid, with good electrical and thermal conductivity like metal, as well as good biocompatibility and room-temperature phase transformation. These remarkable properties have paved the way for the development of novel reconfigurable or stretchable electronics and devices. Despite these outstanding properties, the easy oxidation, high surface tension, and low rheological viscosity of LMs have presented formidable challenges in high-resolution patterning. To address this challenge, various surface modifications or additives have been employed to tailor the oxidation state, viscosity, and patterning capability of LMs. One effective approach for LM patterning is breaking down LMs into microparticles known as liquid metal particles (LMPs). This facilitates LM patterning using conventional techniques such as stencil, screening, or inkjet printing. Judiciously formulated photo-curable LMP inks or the introduction of an adhesive seed layer combined with a modified lift-off process further provide the micrometer-level LM patterns. Incorporating porous and adhesive substrates in LM-based electronics allows direct interfacing with the skin for robust and long-term monitoring of physiological signals. Combined with self-healing polymers in the form of substrates or composites, LM-based electronics can provide mechanical-robust devices to heal after damage for working in harsh environments. This review provides the latest advances in LM-based composites, fabrication methods, and their novel and unique applications in stretchable or reconfigurable sensors and resulting integrated systems. It is believed that the advancements in LM-based material preparation and high-resolution techniques have opened up opportunities for customized designs of LM-based stretchable sensors, as well as multifunctional, reconfigurable, highly integrated, and even standalone systems.
more »
« less
Mechanically Rupturing Liquid Metal Oxide Induces Electrochemical Energy
Abstract Liquid metals, such as Gallium‐based alloys, have unique mechanical and electrical properties because they behave like liquid at room temperature. These properties make liquid metals favorable for soft electronics and stretchable conductors. In addition, these metals spontaneously form a thin oxide layer on their surface. Applications made possible by this delicate oxide skin include shape reconfigurable electronics, 3D‐printed structures, and unconventional actuators. This paper introduces a new approach where liquid metal oxide serves as an electrochemical energy source. By mechanically rupturing their surface oxide, liquid metals form a galvanic cell and convert their chemical energy to electrical energy. When dispersing liquid metals into an ionically‐conductive liquid to form emulsions, this composite material can provide ∼500 mV of open‐circuit voltage and up to ∼4 μWof power. Protected by the naturally occurring oxide skin, the passivating oxide layer of the liquid metal shields it from self‐discharge over time. The device is also stable in harsh environments, such as high temperature or aquatic conditions. Future applications of this device are demonstrated by designing a strain‐activated stretchable battery and a pressure‐sensitive self‐powered keypad. These findings may unlock new pathways to design stretchable batteries and harness their inherent energy for self‐powered robust devices.
more »
« less
- Award ID(s):
- 2047683
- PAR ID:
- 10471192
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 34
- Issue:
- 31
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Gallium‐based liquid metal alloys (GaLMAs) have widespread applications ranging from soft electronics, energy devices, and catalysis. GaLMAs can be transformed into liquid metal emulsions (LMEs) to modify their rheology for facile patterning, processing, and material integration for GaLMA‐based device fabrication. One drawback of using LMEs is reduced electrical conductivity owing to the oxides that form on the surface of dispersed liquid metal droplets. LMEs thus need to be activated by coalescing liquid metal droplets into an electrically conductive network, which usually involves techniques that subject the LME to harsh conditions. This study presents a way to coalesce these droplets through a chemical reaction at mild temperatures (T∼ 80 °C). Chemical activation is enabled by adding halide compounds into the emulsion that chemically etch the oxide skin on the surface of dispersed droplets of eutectic gallium indium (eGaIn). LMEs synthesized with halide activators can achieve electrical conductivities close to bulk liquid metal (2.4 × 104S cm−1) after being heated. 3D printable chemically coalescing LME ink formulations are optimized by systematically exploring halide activator type and concentration, along with mixing conditions, while maximizing for electrical conductivity, shape retention, and compatibility with direct ink writing (DIW). The utility of this ink is demonstrated in a hybrid 3D printing process to create a battery‐integrated light emitting diode array, followed by a nondestructive low temperature heat activation that produces a functional device.more » « less
-
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.more » « less
-
Abstract This review highlights the unique techniques for patterning liquid metals containing gallium (e.g., eutectic gallium indium, EGaIn). These techniques are enabled by two unique attributes of these liquids relative to solid metals: 1) The fluidity of the metal allows it to be injected, sprayed, and generally dispensed. 2) The solid native oxide shell allows the metal to adhere to surfaces and be shaped in ways that would normally be prohibited due to surface tension. The ability to shape liquid metals into non‐spherical structures such as wires, antennas, and electrodes can enable fluidic metallic conductors for stretchable electronics, soft robotics, e‐skins, and wearables. The key properties of these metals with a focus on methods to pattern liquid metals into soft or stretchable devices are summari.more » « less
-
Abstract The practical applications of skin‐interfaced sensors and devices in daily life hinge on the rational design of surface wettability to maintain device integrity and achieve improved sensing performance under complex hydrated conditions. Various bioinspired strategies have been implemented to engineer desired surface wettability for varying hydrated conditions. Although the bodily fluids can negatively affect the device performance, they also provide a rich reservoir of health‐relevant information and sustained energy for next‐generation stretchable self‐powered devices. As a result, the design and manipulation of the surface wettability are critical to effectively control the liquid behavior on the device surface for enhanced performance. The sensors and devices with engineered surface wettability can collect and analyze health biomarkers while being minimally affected by bodily fluids or ambient humid environments. The energy harvesters also benefit from surface wettability design to achieve enhanced performance for powering on‐body electronics. This review first summarizes the commonly used approaches to tune the surface wettability for target applications toward skin‐interfaced sensors and devices. By considering the existing challenges, one also discusses the opportunities as a small fraction of potential future developments, which can lead to a new class of skin‐interfaced devices for use in digital health and personalized medicine.more » « less
