Self-sintering liquid metal colloidal inks for facile manufacture of stretchable conductors

Abstract

As soft robotic, bio-integrated and wearable systems proliferate, the need for stretchable conductors follows. In order to instrument such highly deformable systems with electronics for sensing, communication, and power, similarly soft and stretchable conductors are required. Liquid metals are an attractive material solution because they possess both metallic conductivity and mechanical properties of a fluid. In particular, eutectic gallium-indium alloy (eGaIn) is of interest because gallium at the surface will rapidly oxidize in the presence of oxygen. While this non-conductive surface oxide layer can be problematic when trying to pattern the bulk material, this oxide shell acts to stabilize eGaIn nano- and microparticles. Colloidal suspensions of these particles are much more amenable to scalable manufacturing methods, and the oxide surface can serve as a tunable process handle that can be readily modified. Here, we leverage the oxide formation and modify its composition to facilitate the patterning and formation of stretchable conductive traces. We demonstrate that drying eGaIn microparticles from a water-containing solution results in a self-sintering phenomenon where liquid metal particles will coalesce into a conductive trace upon evaporation of the solvent. We characterize the eGaIn colloidal system and demonstrate its utility as a stretchable conductor.