Computational efficient, quasi-3D model for designing body wearable thermoelectric generators and experimental verification.

Harvesting body heat using thermoelectricity provides a promising path to realizing self-powered, wearable electronics that can achieve continuous, long-term, uninterrupted health monitoring. This paper reports a flexible thermoelectric generator (TEG) that provides efficient conversion of body heat to electrical energy. The device relies on a low thermal conductivity aerogel–silicone composite that secures and thermally isolates the individual semiconductor elements that are connected in series using stretchable eutectic gallium-indium (EGaIn) liquid metal interconnects. The composite consists of aerogel particulates mixed into polydimethylsiloxane (PDMS) providing as much as 50% reduction in the thermal conductivity of the silicone elastomer. Worn on the wrist, the flexible TEGs present output power density figures approaching 35 μWcm⁻² at an air velocity of 1.2 ms⁻¹, equivalent to walking speed. The results suggest that these flexible TEGs can serve as the main energy source for low-power wearable electronics.

We report a spray deposition technique for patterning liquid metal alloys to form stretchable conductors, which can then be encapsulated in silicone elastomers via the same spraying procedure. While spraying has been used previously to deposit many materials, including liquid metals, this work focuses on quantifying the spraying process and combining it with silicones. Spraying generates liquid metal microparticles (~5 μm diameter) that pass through openings in a stencil to produce traces with high resolution (~300 µm resolution using stencils from a craft cutter) on a substrate. The spraying produces sufficient kinetic energy (~14 m/s) to distort the particles on impact, which allows them to merge together. This merging process depends on both particle size and velocity. Particles of similar size do not merge when cast as a film. Likewise, smaller particles (<1 µm) moving at the same speed do not rupture on impact either, though calculations suggest that such particles could rupture at higher velocities. The liquid metal features can be encased by spraying uncured silicone elastomer from a volatile solvent to form a conformal coating that does not disrupt the liquid metal features during spraying. Alternating layers of liquid metal and elastomer may be patterned sequentially to build multilayer devices, such as soft and stretchable sensors.

This paper reports the thermal conductivity and mechanical properties of Sylgard 184 polydimethylsiloxane (PDMS) elastomer loaded with graphene nano-platelets (GnPs) and eutectic Ga-In (EGaIn) liquid metal droplets. We fabricated samples with different GnP and EGaIn concentrations and measured their thermal conductivity using the steady-state absolute technique. The results show that the thermal conductivity of the elastomer can be enhanced up to 5.6X when both GNP and EGaIn are included in the elastomer. Without EGaIn, the enhancement is limited to 4.4X. The results suggest that EGaIn inclusion did not change the viscosity of the uncured material significantly at any GnP loading level. We also observed that addition of just EGaIn to PDMS did not have a significant impact on the material’s stiffness while lowering its ultimate tensile strength by a factor of 2X and the maximum elongation at the break point by a factor of 1.6X. On the other hand, it was demonstrated that GnP addition to pure PDMS or EGaIn doped PDMS made the elastomer stiffer and less tear resistant with lower elongation at the break point.