Biphasic Liquid Metal Composites for Sinter-Free Printed Stretchable Electronics

This work introduces and presents a comprehensive study on a series of biphasic liquid metal (LM) composites that benefit from high conductivity, excellent stretchability, a low gauge-factor, excellent adhesion to a wide range of substrates, for sinter-free writing complex stretchable circuits. These trinary material systems are composed of a block-co-polymer binder, EGaIn liquid metal, and a microparticle (mu P) filler (Ag flakes, Ag-coated-Ni, Ag-coated-Fe, Ni, Ferrite, or TiC). They combine the fluidic behavior, resilience, and self-healing properties of LMs, and the printability, adhesion, and elastic integrity of elastomers. Unlike the previous efforts with LM-polymer composites and printed EGaIn nanodroplets, these composites are intrinsically conductive and do not require any thermal/optical/mechanical sintering. The binary combinations (LM-SIS, LM-Ag, Ag-SIS) are first synthesized and characterized, and then the trinary LM-mu P-SIS composites are evaluated. This includes analysis of microstructure, surface roughness, conductivity, electromechanical coupling, and LM smearing/leakage during mechanical loading, as well as the examination of the influence of filler particle size and composition. It is found that a binary combination of Ag-EGaIn or EGaIn-SIS does not result in the desired properties, and only trinary combination with conductive mu P, preferably Ag, results in a printable, stretchable and sinter-free composite. As an application, a digitally-printed epidermal sticker for respiration monitoring is demonstrated.

Automated summary

This study introduces a new type of biphasic liquid metal composite that enables sinter-free writing of stretchable circuits. The trinary material system exhibits high conductivity, excellent stretchability, low gauge-factor, and strong adhesion to various substrates. The composite combines the fluidic behavior, resilience, and self-healing properties of liquid metals with the printability, adhesion, and elastic integrity of elastomers. The study demonstrates that the introduction of conductive microparticle fillers, particularly silver, is essential for achieving printable, stretchable, and sinter-free composites.