The thermal composite is fabricated by shear mixing EGa In alloy (75% Ga, 25% In, by weight; Gallium Source) with an uncured silicone elastomer (Ecoflex 00-30; Smooth-On) ( coating that helps prevent coalescence and eliminates the need to add surfactants or other dispersing agents (24).The droplets have a statistically uniform spatial distribution and are polydisperse, with a median diameter of ∼15 μm (19).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.Thermal conductivity is measured using the transient hotwire (THW) method in which an embedded wire simultaneously acts as a resistive heat source and thermometer that measures the change in temperature (Δ) increases, thermal conductivity increases (Fig. These values are in good agreement with theoretical predictions obtained from the Bruggeman effective medium theory (EMT) formulation (25) for a uniform dispersion of spherical EGa In inclusions [) in the stress-free state.The programmed sample refers to a composite that has been stretched to 600% strain and then relaxed to an unloaded state.
) Schematic illustration of the LMEE composite where LM microdoplets are dispersed in an elastomer matrix and, upon deformation, the LM inclusions and elastomer elongate in the direction of stretching.Compared with previous attempts with LM-filled elastomers (12), we have discovered that strain creates thermally conductive pathways through the in situ elongation of the deformable liquid inclusions, which significantly enhances thermal conductivity in the stretching direction.For permanent (stress-free) and strain-controlled elongation of the LM inclusions, this enhanced , the exceptional combination of high thermal conductivity, low elastic modulus, and high strain limit allows the LMEE composites to occupy an uncharted region of the material properties space.() Alternating strips of LMEE and unfilled elastomer are heated with a heat gun, and the IR photo time sequence shows the LMEE dissipating heat more rapidly than the elastomer (images correspond to t = 0, 5, 10, and 15 s after the heat source is removed).(Scale bar, 25 mm.) ( = 50% LMEE composites described here occupy a unique region of the material properties space when comparing thermal conductivity with the ratio of strain limit to Young’s modulus. 2, 9, 12, and 14.) The LM embedded elastomer (LMEE) is composed of a Pt-catalyzed silicone elastomer embedded with a randomly distributed, polydisperse suspension of nontoxic (21), liquid-phase eutectic gallium−indium (EGa In) microdroplets (19, 20, 22). 1 and Movie S1, stretched and twisted strips of LMEE exhibit rapid thermal dissipation compared with adjacent strips of unfilled elastomer subject to the same initial heating.