Intrinsically Conductive Liquid Metal‐Elastomer Composites for Stretchable and Flexible Electronics

Liquid metal‐embedded elastomers (LMEEs) are a class of deformable composites made of particles of liquid metal dispersed in an elastomeric matrix. Although these composites possess high thermal conductivity, they are not intrinsically electrically conductive unless a stimulus is applied to join the liquid metal inclusions into a conductive pathway. LMEEs with intrinsic conductivity, especially with a conductive surface, have great potential uses in flexible and stretchable electronics as soft, nondamaging contacts for device characterization, stretchable interconnects for deformable circuits, and as a “soft solder” to electrically connect devices to flexible and stretchable substrates. Here, a simple process is introduced to fabricate intrinsically conductive LMEEs (iLMEEs) with conductive surfaces through the sedimentation of microparticles of eutectic gallium‐indium alloy (EGaIn) in the elastomer poly(dimethylsiloxane). During this sedimentation process, an EGaIn‐rich 3D percolation network forms at the bottom surface. The resulting iLMEE possesses a conductive surface comprising a mosaic of EGaIn particles embedded in PDMS, with a low sheet resistance of 0.63 ± 0.04 Ω sq–1. iLMEE is soft, stretchable, and exhibits stable conductivity to 100% strain. We demonstrate the use of iLMEE as nondamaging, reusable soft electrical contact probes and as mechanically robust electrical connections between light‐emitting devices and flexible plastic substrates. Liquid metal particles embedded in elastomer typically require a mechanical stimulus to sinter the particles to achieve conductivity. This study presents composites that form a conductive network spontaneously, during sedimentation. These intrinsically conductive composites are useful as nondamaging contacts for device characterization and as a “soft solder” to electrically connect devices to flexible substrates.