Liquid Metal Gel Ink with Self-Activating Conductivity for 3D Printing of Multifunctional Electronics.

Liquid metal inks have emerged as promising conductive inks for the printing of soft circuits and multifunctional electronics. However, the printed patterns are typically nonconductive due to the native insulating oxide layer surrounding the liquid metal (LM) particles, which requires mechanical or chemical post-treatments to restore their electrical performance. In this study, the design and preparation of a self-activating LM gel ink are presented. This viscous gel ink consists of LM particles and supramolecular assemblies, which are formed by β-cyclodextrin (β-CD) and sodium dodecyl sulfate (SDS). These assemblies entangle to create a supramolecular gel network, which prevents the LM particles from settling and facilitates 3D printing. Moreover, the supramolecular assemblies are dissociated into host-guest complexes upon heating to 50 °C, thereby allowing the ink to transition its viscosity from ≈13 to ≈0.005 Pa·s at a shear rate of 1 s. This viscosity transition leads to the sedimentation of LM particles, resulting in the formation of a continuous liquid metal phase upon water evaporation, with a high electrical conductivity of 3.4 × 10 S m. The printed conductive patterns can subsequently be used in multifunctional devices, including stretchable displays, wireless power-transmission circuits, and fabric bioelectrodes.