Study on the design of liquid metal-based ink and printing process for direct ink writing of stretchable electronics devices

Abstract

Liquid metal is being regarded as a promising material for soft electronics owing to its distinct combination of high electrical conductivity comparable to that of metals and exceptional deformability derived from its liquid state. However, the applicability of liquid metal is still limited due to the difficulty in simultaneously achieving its mechanical stability and initial conductivity. Furthermore, reliable and rapid patterning of stable liquid metal directly on various soft substrates at high-resolution remains a formidable challenge. To overcome these limitations, in this thesis, the design strategy for custom liquid metal ink that can utilize the characteristics of the direct ink writing printing process is presented, and the development of the meniscus-guided printing process for the ink is discussed. Ink for the meniscus-guided direct ink writing printing includes liquid metal microgranular particles attached to a polyelectrolyte in an acidic water-soluble solvent. Next, meniscus-guided printing based on a direct ink writing method capable of printing a stretchable conductor having initial conductivity, robust adhesion on substrates, and electromechanical stability using this ink is presented. Liquid metal microgranularparticle printed in the evaporative regime is mechanically stable, initially conductive, and patternable down to 50 μm on various substrates. To validate the simplicity, versatility, and reliability of this manufacturing strategy, a ultra-stretchable (~500% strain) electrical circuit, customized electronic skin, and zero-waste ECG sensor were demonstrated, verifying the potential for broad application in the development of advanced soft electronic devices.