CAREER: Manufacturing of Solid Particle-Liquid Metal Mixtures for Soft Robotics and Stretchable Electronics

This Faculty Early Career Development (CAREER) grant establishes a scalable manufacturing approach for incorporating diverse solid particle additives into room temperature liquid metals by controlling their reactivity and wetting characteristics through an interfacial engineering approach. This work provides new fundamental knowledge that enables the creation of a novel class of multiphase conductive pastes with customizable physical, rheological, and chemical properties. The enhanced properties increase the suitability of using liquid metal pastes for extrusion-based three-dimensional (3D) printing and lead to new applications in soft robotics and stretchable electronics, which contribute to the economic and societal advancement of U.S. manufacturing. The solid particle-liquid metal mixtures are suitable materials for additive manufacturing of a variety of applications such as control systems, soft matter actuators, and distributed sensors. The research is complemented by new learning modules that seek to actively engage students across the educational spectrum by integrating entrepreneurial literacy with research-based activities focused on additive manufacturing, materials processing, and digital modeling. These modules are delivered through local programs and via a mobile science lab to schools and teachers across Nebraska and elsewhere to enhance classroom learning for ethnically, geographically, and socio-economically diverse students. The goal of this research is to establish a universal strategy for incorporating solid particle additives into liquid metals to enhance their physical and rheological properties without compromising their fluidic attributes. Typically, the solid particle additive is a metal such as nickel, tungsten, or copper and the liquid metal is gallium or its compounds. The high reactivity and cohesive energy of gallium-based liquid metals offer challenges at the solid-liquid interface, which are overcome through an interfacial engineering approach where an intermediate layer is introduced to concurrently act as a corrosion barrier and wetting agent. The solid particle-liquid metal mixtures are created by mixing via mechanical shear under controlled conditions. The physical properties, rheological behavior, and chemical stability are subsequently characterized to establish the process-property-performance relationships to understand how the particle composition, volume loading, and size affect the properties and performance of the particle-liquid metal mixtures. The improved properties, enhanced chemical stability, and ability to pattern structures in three-dimensions enable particle-liquid metal mixtures to take a range of forms, from discrete inclusions in composite materials to patterned liquid networks. This research enables the design and manufacturing of materials and structures tailored for soft structures, devices and systems inspired by biology. This project is jointly funded by the Advanced Manufacturing (AM) Program, the Established Program to Stimulate Competitive Research (EPSCoR), and the Civil, Mechanical and Manufacturing Innovation (CMMI) Division. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.