High thermal conductivity in soft elastomers with elongated liquid metal inclusions

Abstract

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 ) under stress-free conditions and a ∼50× increase (9.8 ± 0.8 W·m) 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.liquid metal | thermal conductivity | soft materials | soft robotics | stretchable electronics

Untethered soft robotics

“…Recent work has achieved SMA-powered locomotion, addressing this problem of overheating by precisely controlling the voltage applied to the SMA 52 (Fig. 2e), employing active cooling with water 53 or air 54 , or maximizing the heat dissipation by incorporating a thermally conductive soft elastomer 55 (Fig. 2f).…”

“…Referring to Fig. 5, these include implementations that contain SMAs 54,55 (Fig. 5a,b), DEAs 63,68,117 (Fig.…”

“…This comes either in the form of electronics-free, microfluidic sensors [110][111][112] , or NFC induction coils that can briefly power wearable devices with electromagnetic waves in order to allow sensor reproduced from ref. 55 , National Academy of Sciences (a); ref. 54 , IEEE (b); ref.…”

“…Furthermore, as soft systems become more complex, efficient heat management will become critical to designing functional soft electrical components. Creating and integrating soft thermally conductive materials 55 and polymers will help enable these advances. Finally, as these efforts produce increasingly mobile soft robots, research into their environmental impact (for example, using biodegradable structural materials 135 ) should also be pursued.…”

Ga‐Based Liquid Metal Micro/Nanoparticles: Recent Advances and Applications

“…LM particles with a high thermal conductivity (26.4 Wm −1 K −1 at 30 °C) can be used as soft materials to improve heat transfer capabilities. Bartlett et al prepared a soft‐matter composite in which LM microdroplets were dispersed in a highly deformable elastomer. When the sample of LM‐embedded elastomer (volume fraction of LM = 50%) was stretched to 600% strain and then relaxed to an unloaded state, the thermal conductivity of the LMEE sample in longitudinal direction ( k y ) was enhanced to 4.7 ± 0.2 Wm −1 K −1 , ≈25 times higher than that of the base polymer ( Figure a).…”