3D laser activatable alloy-free solid/liquid biphasic conductive composites for additive manufacturable electronics

Recently, biphasic soft conductors have gained tremendous attention owing to their characteristic advantages by co-existence of solid and liquid metals. In this study, we developed the 3D printable composite that can generate alloy-free solid/liquid biphasic conductive features by 3D green-laser activation process. It comprises copper nanoparticles with localized surface plasmonic resonance in the visible wavelength regime, eutectic indium-gallium liquid metal droplets, and polyvinylpyrrolidone as a multifunctional polymeric additive. We clarify that, based on the photothermal simulation results, an instant thermal heating is triggered in the vicinity of copper nanoparticles upon green laser irradiation, which activates, comprehensively, the overall microstructural evolution reactions, including a rupture of the oxide shell surrounding the liquid metal droplets, a formation of networked copper particulate assemblies, and a combustion-free carbonization of polymeric substances. This allows us to generate double-layered biphasic conductive features in which the solid conductive compartments are in individual contact with the densified liquid metal bulks, enabling to achieve a high conductivity, excellent flexibility, self-healing capability, and solder processability without the critical problem of leakage of liquid metals.