Collaborative Research: Interfacial Self-healing of Nanocomposite Hydrogels

自修复聚合物是一种无需人工干预就能自动修复损伤的合成材料。它们在各种工程应用中显示出巨大的可持续技术潜力，包括人造肌肉和皮肤、柔性电子、软机器人等。然而，最先进的自修复聚合物设计仍然处于试验和错误阶段，缺乏理论指导。该奖项支持阐明纳米复合水凝胶（由纳米颗粒交联的水介导聚合物网络组成）自愈机制的基础研究。从该项目中获得的知识将为能够在损伤后恢复其功能的自修复聚合物提供机械见解。这项研究不仅可以促进自愈力学的基础科学，而且可以通过进一步发展和提高基于软材料的可持续技术来促进国家的健康、繁荣和福利。该项目还将培养固体力学、聚合物科学、机械工程和高性能计算领域的多元化学生，以培养下一代劳动力。该项目的教育目标将通过课程开发、本科生研究机会、高中生暑期研究计划、K-12教师研究经验计划和K-12外展计划来实现。我们将特别努力让代表性不足的学生参与这个项目。尽管在自修复聚合物的合成和应用方面进行了广泛的研究，但构建自修复性能与材料/愈合设置之间的机制关系仍然具有挑战性。关键的技术障碍是如何物理模拟聚合物网络在自愈过程中的微观结构演变。该项目的中心假设是，纳米复合水凝胶的自愈强度是由聚合物链在断裂界面上的扩散以及随后与纳米颗粒形成的交联所控制的。为了验证这一假设，本项目将分子动力学模拟与分析理论相结合，研究聚合物链在自愈过程中的微观扩散反应行为和自愈后的宏观界面强度。计算和理论预测将通过实验研究系统地验证纳米复合水凝胶，这些纳米复合水凝胶由几种材料组成，如颗粒浓度、颗粒大小和水分数，以及在各种外部愈合控制下，如温度和延迟时间。跨学科的努力将为定量理解自愈聚合物的多尺度力学开辟有希望的途径，并提供高性能自愈聚合物的基本设计原则。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.