Development of fibrous liquid-metal conductors with adaptive confinement of polymer network for stretchable electronic interconnects

Most issues in stretchable electronics come from the interfacial connections between different parts which frequently undergo stress/strain concentration. In particular, the interface mismatch between stretchable conductors and rigid microelectronics results inirreversible changes in electrical resistance and permanent interface failure. Designing flexible interconnects that can bridge mechanical mismatches and maintain reliable conductive contact is therefore highly desired. Gallium-based liquid metals (LMs) with a unique combination of metallic conductivity, low toxicity, and fluidity at room temperature have emerged as a promising class ofmaterials for the development of stretchable electronics. Considering their high surface energy which may cause depletion from coated substrates, LMs are usually blended and processed with various polymers to form flexible LM-polymer composites for furtherdevelopment of flexible conductors. However, there are critical issues in the development and application of LM-based flexible conductors. (1) They are not inherently conductive due to a thin layer of polymer that forms between the LM particles. (2) Post-treatments using mechanical forces and lasers can assist sintering of the LM particles within the composites, but the performance of the processed samples varies due to the irreversible damages of the polymer network. (3) They show limitations in interconnecting with microelectronics when service in stretchable electronics: encapsulation is typically applied to prevent the leaking of LMs, but this also makes the conductors less functional for soldering and welding. Targeting at these challenges, in this project, we aim to develop an easy-to-use toolbox of fibrous liquid-metal conductors and corresponding processing technologies for the fabrication of stretchable electronic interconnects. Our preliminary studies show that the dynamic confinement derived from a stretchable-yet-adhesive polymer network can effectively stabilize the conductive path of the liquid-metal conductor and offer high adhesion to diverse surfaces, allowing for efficient soldering. Leveraging the dynamic bonding nature and the confinement effect of the polymer network, we propose thatfibrous liquid-metal conductors with large surface-volume ratios and high LM loading ratios may potentially overcome the issues facing by bulk composite films, and thus they can be welded and integrated into various patterns and structures for the fabrication ofelectronic interconnects. The outcome of this project will not only advance our fundamental understanding on the surface science of LM-polymer assemblies, but also provide new insights into the design of flexible condoctors and electronic interconnects which will benefit their potential applications in wearable electronics, IoT devices, and healthcare-related applications.