In Situ Deposition of Skin-Adhesive Liquid Metal Particles with Robust Wear Resistance for Epidermal Electronics

Liquid metal (LM) is increasingly employed as a conductive filler in soft and flexible elastomer composites owing to its favorable conductivity and liquid fluidity. However, the high density of LM inevitably increases the weight of composites, which brings limitations in large-area and weight-sensitive applications. This work reports a flexible and stretchable elastomer composite composed of pod-like contacting lightweight LM foam spheres and polydimethylsiloxane matrix (LMS/PDMS). The lightweight LMS reduces the amount of LM used in the preparation process while imparting good electrical conductivity and deformability to the composite. The different contact modes of LMS endow the final composites with diverse strain sensitivity. The mechanism of interfacial contact conduction between the LMS with different melting points has been systematically studied, and the result shows that the liquid–solid contact mode of LMS further improves the strain sensitivity of the composite. Moreover, the composite also has satisfactory electrothermal properties and the temperature can quickly reach 70 °C within 30 s, showing good applicability in electric heating. Finally, the composites containing LMS with different contact modes can be developed as multifunctional sensors to detect human activities, temperature variation, and even underwater vibration, demonstrating the great potential in next-generation sensors and electronics.

Section: Introductionmentioning

confidence: 99%

Flexible and Stretchable Elastomer Composites Based on Lightweight Liquid Metal Foam Spheres with Pod-like Contacts

Xuan

et al. 2023

“…A few efforts have been devoted to increasing the mechanical reliability of LM circuits by converting its liquid state into a biphasic (solid−liquid) state through heat treatment, 33,34 the use of pulsed laser lithography to obtain self-packaged structures, 35 or in situ deposition of adhesive LM particles by chemical modification. 36,37 thermally sensitive substrates, or the use of expensive equipment. Thus, it is highly needed to develop a simple and versatile way to create robust LM circuits for reliable use.…”

Section: Introductionmentioning

confidence: 99%

“…For the surface patterning, the liquid nature of LM conductors makes them prone to mechanical damage, requiring additional encapsulation steps to protect the delicate LM circuits. − Encapsulated LM cannot directly contact other objects and expose to the environment, limiting their practical use in many important application scenarios such as wearable and implantable electrophysiology monitoring, electrostimulation, and gas and temperature sensing. A few efforts have been devoted to increasing the mechanical reliability of LM circuits by converting its liquid state into a biphasic (solid–liquid) state through heat treatment, , the use of pulsed laser lithography to obtain self-packaged structures, or in situ deposition of adhesive LM particles by chemical modification. , However, these strategies have resulted in multistep operation for pretreatment and patterning of LM, being incompatible with thermally sensitive substrates, or the use of expensive equipment. Thus, it is highly needed to develop a simple and versatile way to create robust LM circuits for reliable use.…”

Section: Introductionmentioning

confidence: 99%

Surface-Embedded Liquid Metal Electrodes with Abrasion Resistance via Direct Magnetic Printing

Zhang

Chen

et al. 2022

Gallium-based liquid metals (LMs) featuring both high conductivity and fluidity are ideal conductors for soft and stretchable electronics. However, their liquid nature is a doubleedged sword in many key applications since LMs are inherently prone to mechanical damage. Although additional encapsulation is frequently used for the protection of delicate LM electrodes, it hinders the electrical interfacing with other objects for interconnection, sensing, and stimulation. Here, different from conventional patterning methods that deposit LM on or inside substrates, we for the first time report a simple strategy to create surface-embedded LM of eutectic gallium-indium (EGaIn) circuits with mechanical damage endurance. This was achieved by using direct magnetic printing to overcome the high surface tension of LM, allowing it to be passively filled into the laser-patterned microgrooves on soft substrates. We show that the surface-embedded LM circuits are resistant to mechanical erasure, washing, and peeling. We also show the applications of our surface-embedded LM electrodes in respiration monitoring and electrical stimulation of nerves. This work provides a simple and efficient way to create mechanically reliable LM microelectrodes, holding great promise for wearable and implantable bioelectronics.

“…Owing to the challenges encountered in the fabrication of LM-based stretchable conductors by direct deposition of bulk LMs on flexible substrates, deposition, and printing of LM micro- and nanodroplet inks are favorable since mechanical or laser-induced sintering of LM droplets can establish conductive paths on the substrates. − However, this strategy has several drawbacks, for instance, low conductivity, weak adhesion to substrates, requiring high accuracies of space and force for sintering, and it is only feasible for rather small areas. In some cases, surface modification of LM droplets can be employed to improve the adhesive properties of the LM pattern and even eliminate the mechanical sintering process. − …”

Section: Introductionmentioning

confidence: 99%

Conformally Adhesive, Large-Area, Solidlike, yet Transient Liquid Metal Thin Films and Patterns via Gelatin-Regulated Droplet Deposition and Sintering

Gan

Xiao

Handschuh‐Wang

et al. 2022

Adhesion and spreading of liquid metals (LMs) on substrates are essential steps for the generation of flexible electronics and thermal management devices. However, the controlled deposition is limited by the high surface tension and peculiar wetting and adhesion behavior of LMs. Herein, we introduce gelatin-regulated LM droplet deposition and sintering (GLMDDS), for the upscalable production of conformally adhesive, solidlike, yet transient LM thin films and patterns on diverse substrates. This method involves four steps: homogeneous deposition of LM microdroplets, gelation of the LM-gelatin solution, toughening of the gelatin hydrogel by solvent displacement, and peeling-induced sintering of LM microdroplets. The LM thin film exhibits a three-layer structure, comprising an LM microdroplet-embedded tough organohydrogel adhesion layer, a continuous LM layer, and an oxide skin. The composite exhibits high stretchability and mechanical robustness, conformal adhesion to various substrates, high conductivity (4.35 × 105 S·m–1), and transience (86% LM recycled). Large-scale deposition (i.e., 5.6 dm2) and the potential for patterns on diverse substrates demonstrate its upscalability and broad suitability. Finally, the LM thin films and patterns are applied for flexible and wearable devices, i.e., pressure sensors, heaters, human motion tracking devices, and thermal management devices, illustrating the broad applicability of this strategy.