Application of Oxidized Lignin Encapsulated Liquid Metal Prepared Conductive Ink for Sustainable Flexible Electronics

Gallium–indium liquid metal (LM) exhibits both metallic conductivity and the ability to flow as a liquid at room temperature, rendering it an excellent conductor for flexible electronics based on paper. Nevertheless, the high surface tension of LM and its limited affinity for paper pose considerable difficulties in achieving precise patterns. Oxidized lignin (OL), prepared by alkali lignin (AL) through ozone oxidation, contains a large number of phenol hydroxyl and carboxyl groups on the surface, can adhere to the surface of liquid metal (LM), and has good self-assembly performance. In this study, we propose employing OL-encapsulated liquid metal microparticles (LMP-OL) as a conductive ink. The formulated ink demonstrates commendable stability, remarkable adsorption capacity, and the ability to swiftly print conductive patterns on paper. LMP-OL ink showcases outstanding adsorption, conductivity, and Joule heating behavior. Moreover, this investigation explores diverse integrated functionalities such as capacitive touch sensing, respiratory monitoring, and thermal management by directly spraying the ink onto paper, skin, and clothing using 3D printing technology. Most significantly, the circuits printed with LMP-OL ink are recyclable.