Avalanche Coalescence of Liquid Metal Particles for Uniform Flexible and Stretchable Electrodes

Abstract Self‐sinterable gallium‐based liquid metal (LM) ink for a handy drop‐casting coating method is developed. The fabricated LM electrode is coffee‐ring‐free and bilayer‐free, which guarantees high electrical conductivity, wettability, flexibility, and stretchability. The ink consists of Galinstan, ethanol‐water mixture, hydrochloric acid, and polyvinylpyrrolidone. The binary mixture provides excellent wetting conditions and suppresses a coffee‐ring stain from Marangoni mixing. The acid removes an oxide layer on the LM interface. The colloidal interaction forces by self‐assembled polyvinylpyrrolidone induce avalanche coalescences of the particles at the end of evaporation, which produces a thin and uniform dried conductive layer. The acid and polymer provide a bilayer‐free structure and electrification without any post sintering. The drop‐casted self‐transformed LM electrode showed excellent electrical resistance of O (0.1–1 Ω) on folding and stretching conditions. It is believed that this method can serve as flexible and stretchable electrodes, on various substances for soft robots and wearable devices, without any complicated post‐process.