Rapidly reversible discoloration of liquid metal by contact or separation

Silver-white liquid metals (LMs), such as gallium (Ga), eutectic gallium-indium (EGaIn) and gallium-indium-tin (GaInSn) are becoming increasingly important functional materials in macroscopic bionic robots for their strong room temperature deformation capacities. However, their shiny color makes them particularly easy to be detected and "terminated". Therefore, how to naturally blend in with the surroundings and possess the contact discoloration capacities like the cyborg T-1000 terminator secretly crawling out of the chessboard floor in the movie, is what sci-fi fans are striving to pursue. Herein, we show a rapidly reversible silver-white to dark brown discoloration of LM GaInSn induced merely by being touched by or separated from a piece of rough surface graphite paper. Enhanced charge transfer by rough graphite paper constitutes the main reason for the contact induced discolorations. This work should suggest an exciting way for camouflage, light harvest skin materials on LM smart bionic soft robots.