Intrinsically conductive and nano-scale reconfigurable liquid metal nano-capsules

Abstract

Liquid metal (LM), particularly Gallium-based alloy, has emerged as an indispensable material for artificial skins, offering vast potential in wearable prophylactic medicine, AI-based human-machine interfaces, bodily-kinesthetic monitoring, etc. Nanosized LM has been adopted to facilitate its processability in various LM-elastomer interfaces, stretchable circuits, and dynamic self-healing devices. However, a naturally formed electrical-passive oxidation layer (Ga2O3) on LM nanoparticles would impede electron transportation, rendering the original LM nanoparticles nonconductive even when they are compacted together. Attempts, e.g., mechanical activation and chemical-assisted erosion, have been developed to remove this electrical barrier, but lead to other issues, including circuit short, weaken interfacial bonding, and unforeseen activation. Here, intrinsically conductive LM nano-capsules were proposed to address these issues. These nano-capsules are in situ encapsulated by platinum@redox graphene oxide (Pt/rGO) and exhibit an intrinsically high conductivity (up to 1.2 × 106 S m−1). The encapsulation process was assisted by oxidation layer thinning and particle-to-particle bridging through polyelectrolyte (PSS). As a result, the Pt/rGO tow-dimensional layer effectively can be encapsulated on LM nanoparticles via electrostatic interaction to enable conductivity of the shells of nano-capsules. And the highly compact and reconfigurable profile of the LM nano-capsules can be developed for highly conductive circuits. The LM nano-capsules maintain chemical and mechanical stability against external stimuli, including long-term exposure (up to 7 days in solvent and 30 days in air) and mechanical deformations (ΔR/R0 < 4% after 5000 stretching cycles under strain of 100%). And the LM capsule ink shows easy access to design printable circuits (∼70 μm) and fabricate electronic tattoos for robotic sensory skins and real-time health-monitoring technologies.