Significance Efficient thermal transport is critical for applications ranging from electronics and energy to advanced manufacturing and transportation; it is essential in emerging domains like wearable computing and soft robotics, which require thermally conductive materials that are also soft and stretchable. However, heat transport within soft materials is limited by the dynamics of phonon transport, which results in a trade-off between thermal conductivity and compliance. We overcome this by engineering an elastomer composite embedded with elongated inclusions of liquid metal (LM) that function as thermally conductive pathways. These composites exhibit an extraordinary combination of low stiffness (<100 kPa), high strain limit (>600%), and metal-like thermal conductivity (up to 9.8 W⋅m−1⋅K−1) that far exceeds any other soft materials. Soft dielectric materials typically exhibit poor heat transfer properties due to the dynamics of phonon transport, which constrain thermal conductivity (k) to decrease monotonically with decreasing elastic modulus (E). This thermal−mechanical trade-off is limiting for wearable computing, soft robotics, and other emerging applications that require materials with both high thermal conductivity and low mechanical stiffness. Here, we overcome this constraint with an electrically insulating composite that exhibits an unprecedented combination of metal-like thermal conductivity, an elastic compliance similar to soft biological tissue (Young’s modulus < 100 kPa), and the capability to undergo extreme deformations (>600% strain). By incorporating liquid metal (LM) microdroplets into a soft elastomer, we achieve a ∼25× increase in thermal conductivity (4.7 ± 0.2 W⋅m−1⋅K−1) over the base polymer (0.20 ± 0.01 W⋅m−1·K−1) under stress-free conditions and a ∼50× increase (9.8 ± 0.8 W⋅m−1·K−1) when strained. This exceptional combination of thermal and mechanical properties is enabled by a unique thermal−mechanical coupling that exploits the deformability of the LM inclusions to create thermally conductive pathways in situ. Moreover, these materials offer possibilities for passive heat exchange in stretchable electronics and bioinspired robotics, which we demonstrate through the rapid heat dissipation of an elastomer-mounted extreme high-power LED lamp and a swimming soft robot.

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High thermal conductivity in soft elastomers with elongated liquid metal inclusions.

Summary Liquid metal (LM) with high electrical conductivity, thermal conductivity, excellent biocompatibility, and extraordinary fluidity has emerged as a promising class of functional materials. However, such materials still encounter many practical challenges due to the rather limited forms available so far. As a promising remedy, LM composites in synergy with other materials would open tremendous opportunities for fundamental research or practical applications. This is because controllable integration of base LM with functional materials (e.g., metal nanoparticles, polymers, and drug molecules) would significantly tune the intrinsic properties of LM as desired, enabling it to offer further major potential in tackling various sectors' challenging issues, including thermal management, biomedicine, chemical catalysis, flexible electronics, and soft robots. Here, we systematically summarize and review the fundamental progress in pursuing LM composites. The basic composite strategies are outlined in three categories: LM composites with core-shell structure, LM-polymer composites, and LM-particle composites. The effectiveness of the composite strategy is illustrated via the typical applications of LM composites in representative fields. The challenges and perspectives in developing LM composites are also identified and interpreted to better guide future research. It is expected that the coming LM era will witness a new world of fruitful composites thereby discovered or invented.

Liquid Metal Composites

There is little question that the "electronic revolution" of the 20th century has impacted almost every aspect of human life However, the emergence of solid-state electronics as a ubiquitous feature of an advanced modern society is posing new challenges such as the management of electronic waste (e-waste) that will remain through the 21st century In addition to developing strategies to manage such e-waste, further challenges can be identified concerning the conservation and recycling of scarce elements, reducing the use of toxic materials and solvents in electronics processing, and lowering energy usage during fabrication methods In response to these issues, the construction of electronic devices from renewable or biodegradable materials that decompose to harmless by-products is becoming a topic of great interest Such "green" electronic devices need to be fabricated on industrial scale through low-energy and low-cost methods that involve low/non-toxic functional materials or solvents This review highlights recent advances in the development of biodegradable materials and processing strategies for electronics with an emphasis on areas where green electronic devices show the greatest promise, including solar cells, organic field-effect transistors, light-emitting diodes, and other electronic devices

Biodegradable Materials and Green Processing for Green Electronics.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/inf2.12060

Physical sensors for skin-inspired electronics

Flexible materials with the ability to be bent, strained, or twisted play a critical role in soft robots and stretchable electronics. Although tremendous efforts are focused on developing new stretchable materials with excellent stability, inevitable mechanical damage due to long term deformation is still an urgent problem to be tackled. Here, a magnetic healing method based on Fe-doped liquid metal (Fe-GaIn) conductive ink via a noncontact way is proposed. Further, multifunctional flexible electronics are designed with combined performances of superior remote self-healing under magnetic field, water-degradable, and thermal transfer printing, which attribute to three parts of the materials including Fe-GaIn conductive ink, degradable PVA substrate, and adhesive fructose. The as-made light emitting diodes (LED) circuit is demonstrated with both structural and functional repairing after single or multipoint damage. The self-healing time from multipoint damage is pretty fast within 10 s. Due to the water-soluble PVA film, the recycling process is simple via immersing into water. Through heating, the electric circuit on fructose can be transferred to other flexible substrate with high efficiency, which broadens the practical applications of the present system. The novel and multifunctional electronics hold great promise for self-healing electronics, transient electronics, and soft robots.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201901478

Magnetic Liquid Metal (Fe-EGaIn) Based Multifunctional Electronics for Remote Self-Healing Materials, Degradable Electronics, and Thermal Transfer Printing.

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

The invention discloses a liquid metal wireless charging coil and a preparation method thereof. The wireless charging coil comprises a spiral flexible pipeline and liquid metal for filling the flexible pipeline; the inner diameter cross section of the flexible pipeline is 1-4mm; and the two ends of the flexible pipeline are connected with a PCB. By adopting the millimeter-level and large-dimensionflexible pipeline, and by injecting the flexible pipeline with the liquid metal, the liquid metal wireless charging coil is manufactured, so that the cross section of the coil is enlarged, the directcurrent resistance of the coil is lowered, the charging efficiency is highly increased, and energy consumption caused by heating is lowered in a condition of not influencing the inductance value; andin addition, the liquid metal wireless charging coil is high in flexibility, easy to bend and fold, convenient to carry, low in construction cost, recyclable and high in applicability.

Liquid metal wireless charging coil and preparation method thereof

The invention discloses a flexible recoverable circuit and a fabrication method thereof. The fabrication method comprise the steps of providing a polyvinyl alcohol thin film with microflow pipeline; injecting liquid metal into the microflow pipeline; and packing the polyvinyl alcohol thin film to fabricate the flexible recoverable circuit. The problem that a traditional flexible circuit is difficult to recycle is solved.

Ye Shichao

Papers

Liquid Metal‐Based Transient Circuits for Flexible and Recyclable Electronics

Liquid metal wireless charging coil and preparation method thereof

Flexible recoverable circuit and fabrication method thereof