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.