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High Thermal Conductivity in Soft Elastomers with Elongated Liquid Metal Inclusions

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Journal Article - Open Access

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Department of Mechanical Engineering, Carnegie Mellon University Pittsburgh United States

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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 thermalmechanical 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 Youngs 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 approx. 25 increase in thermal conductivity 4.7 or - 0.2Wm1K1 over the base polymer 0.20 or - 0.01Wm1K1 under stress-free conditions and a approx. 50 increase 9.8 or - 0.8 Wm1K1 when strained. This exceptional combination of thermal and mechanical properties is enabled by a unique thermalmechanical 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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