Dynamically crosslinked liquid metal-complexing elastomer as robust solvent-free 3D printing ink for reprocessable flexible electronics

The three-dimensional (3D) printing of thermoset liquid metal (LM)-based flexible electronics holds considerable promise for various applications. However, the high surface tension and density of LM tend to cause sedimentation during the printing process, presenting significant challenges for 3D printing. Additionally, current 3D-printed thermoset LM-based flexible composite materials are not recyclable, resulting in resource wastage. In this work, a disulfide bond-based dynamically crosslinked polyurethane (SPU) is introduced as a solvent-free ink for fabricating an elastomer-liquid metal composite (SPU-LM). The crosslinking units in the SPU-LM ink are designed as Diels-Alder (DA) adducts, which undergo reversible dissociation upon heating, transitioning into a molten state. The multifunctional disulfide bonds facilitate interactions between the LM micro-nanoparticles and the polymer network, improving the dispersion of the LM and preventing sedimentation. These disulfide bonds also enhance the mechanical properties and self-healing capability of the material. The printed SPU-LM wires exhibit excellent stretchability, mechanical durability, near-infrared light-induced self-healing, and conductivity. Notably, these wires retain their mechanical and electrical properties even after multiple printing cycles. The results demonstrate the potential for sustainable printing of LM-based flexible electronics. Furthermore, the LM can be easily recycled, contributing to sustainability in flexible electronics fabrication.