Digitally Printable Magnetic Liquid Metal Composite for Recyclable Soft-Matter Electronics

Abstract

The increasing interest in epidermal patches for wearable monitoring makes it urgent to move toward “greener” and recyclable materials in printed electronics. However, combining scalable fabrication, stretchable function, and recyclable material architecture is challenging to achieve. Herein, this article introduces a printable biphasic liquid metal (LM)-based composite that combines excellent electrical conductivity, high stretchability, low-electromechanical gauge factor, printability, sinter-free functionality, and compatibility with heat-sensitive substrates, thanks to the sinter-free formulation. The novel eutectic gallium indium LM-nickel-styrene-isoprene (SIS) thermoplastic elastomer composite takes advantage of a “greener” solvent composed of a mixture of methyl acetate, cyclohexane, and 4-chlorobenzotrifluoride compared to the toluene used in block copolymers (BCPs). Furthermore, it replaces the costly micron-sized silver flake filler particles with nickel, a lower-cost alternative that enables facile recyclability by using a magnetic force. The use of BCPs with non-permanent physical cross-links enables the possibility of recycling. A green route is shown for recycling the composite, using only bio-friendly acids and daily used products such as sugar and Epsom salt. The application of these composites is shown through the digital printing of stretchable circuits and magnetic switches.