Collaborative Research: Interfacial Self-healing of Nanocomposite Hydrogels

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Self-healing polymers are synthetic materials capable of autonomously repairing damages without human intervention. They have shown great potentials for sustainable technologies in diverse engineering applications, including artificial muscles and skins, flexible electronics, soft robotics and many others. Nevertheless, the state-of-the-art design of self-healing polymers remains at the trial-and-error stage with insufficient theoretical guidance. This award supports fundamental research to elucidate the self-healing mechanics of nanocomposite hydrogels that consist of water-mediated polymer networks crosslinked by nanoparticles. The knowledge obtained from this project will provide mechanistic insights into self-healing polymers that are able to restore their functionality after damage. The research will not only promote the fundamental science of self-healing mechanics, but also advance the national health, prosperity, and welfare through further development and enhancement of soft-materials based sustainable technologies. This project will also train a diverse group of students in the areas of solid mechanics, polymer science, mechanical engineering, and high-performance computing for next-generation workforce development. The educational objectives of the project will be realized through curriculum development, undergraduate research opportunities, summer research program for high school students, research experience for K-12 teachers program, and K-12 outreach program. Special efforts will be made to involve underrepresented students in this project. Despite extensive studies in the syntheses and applications of self-healing polymers, constructing the mechanistic relationship between self-healing properties and material/healing settings remains challenging. The key technical barrier is how to physically model the microstructure evolution of the polymer networks during the self-healing process. The central hypothesis of this project is that the self-healing strength of nanocomposite hydrogel is governed by the diffusion of polymer chains across the fractured interface and subsequent crosslinks formed with nanoparticles. To test this hypothesis, the project integrates molecular dynamics simulations and analytical theories to study microscopic diffusion-reaction behaviors of polymer chains during self-healing process and macroscopic interfacial strengths after self-healing. The computational and theoretical predictions will be systematically validated with experimental studies of nanocomposite hydrogels composed of several material compositions, such as particle concentration, particle size, and water fraction, and under various external healing controls, such as temperature and delaying time. The interdisciplinary effort will open promising avenues for quantitatively understanding the multiscale mechanics of self-healing polymers and providing fundamental design principles of high-performance self-healing polymers.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.