Molecular Understanding and Design of Physically-linked Double Network Hydrogels

非技术总结：聚合物水凝胶作为一种软湿材料，在废水处理、组织工程、药物输送和食品工业中有着广泛的应用，但大多数水凝胶的机械性能较弱，这极大地限制了它们的使用。双网（DN）水凝胶，由两个对比和互穿的聚合物网络组成，被认为是最坚韧的软材料。目前对DN凝胶从合成方法到增韧机理的认识主要来自于化学交联DN凝胶，但缺乏自恢复和自修复的特性。与化学交联的DN凝胶不同，这项工作试图开发一种新型的基于物理的DN水凝胶，它具有优异的机械、自修复、自恢复和机械诱导光学性质。系统地探索化学和物理连接的DN凝胶将有助于更好地理解结构-性能关系，并更好地设计具有其他理想性能的下一代坚韧水凝胶。从该项目中获得的新知识和技术也可能导致工程应用，如坚固的人造组织，自我修复材料，智能应力响应机器人和损伤控制传感器。该项目将为各个层次的学生提供研究机会，包括代表性不足的学生，并帮助发展教科书知识和实践技能，包括聚合物物理、材料化学、分子模拟和工程设计。该项目还将通过课程开发、暑期实习和当地推广活动，整合更广泛的教育方面。技术概述：本项目的主要目标是开发具有高机械强度、自修复性能和机械致发光三种综合性能的新型物理连接双网（DN）水凝胶。通过研究三种物理连接的DN凝胶，有或没有不同的交联剂，PI的小组希望揭示一些基本原理，关于结构网络拓扑之间固有的结构-性质关系，两个网络之间和内部的功能相互作用，以及结构对增韧，自愈和能量耗散机制的依赖。为此，将探索三个任务：第一项任务是研究第一和第二网络对基于物理的DN凝胶的力学性能的功能作用，并了解不同的网络及其相互作用如何影响可观察的力学性能。第二项任务是在保持良好力学性能的同时，研究DN凝胶的自恢复和自修复性能及其机制。与实验任务并行，计算组件将包括结构、动力学和两个网络和交联剂之间的相互作用的研究。此外，将开发一个理论模型来描述网络对机械，自我恢复/愈合特性和能量耗散的依赖。将计算结果与实验结果结合比较，有助于建立物理连接的DN凝胶的宏观性能与不同时间尺度和长度尺度下纳米级网络相互作用之间的关系，最终为新型韧性凝胶的合理设计制定一套规则。

NON-TECHNICAL SUMMARY:While polymer hydrogels as soft-and-wet materials have a wide range of applications for wastewater treatment, tissue engineering, medication delivery, and in the food industry, most hydrogels are mechanically weak which greatly limits their uses. Double network (DN) hydrogels, consisting of two contrasting and interpenetrating polymer networks, are considered as perhaps the toughest soft materials. Current knowledge of DN gels stemming from synthesis methods to toughening mechanisms comes mainly from chemically crosslinked DN gels, but these lack in self-recovery and self-healing properties. Differently from chemically crosslinked DN gels, the proposed work attempts to develop a new class of physically-based DN hydrogels with integrated superior mechanical, self-healing, self-recovery, and mechanically-induced optical properties. Systematic exploration of both chemically- and physically-linked DN gels will enable a better fundamental understanding of structure-property relationships and a better design of next-generation tough hydrogels with other desirable properties. New knowledge and techniques derived from this project may also lead to engineering applications such as robust artificial tissues, self-healing materials, smart stress-responsive robots, and damage-control sensors. The project will provide research opportunities to students at all levels, including underrepresented students, and help develop textbook knowledge and hands-on skills in polymer physics, materials chemistry, molecular simulations, and engineering design. The project will also integrate broader educational aspects via curriculum development, summer internships, and local outreach activities.TECHNICAL SUMMARY:The main objective of this project is to develop new physically-linked double-network (DN) hydrogels with three integrated properties of highly mechanical strength, self-healing properties, and mechanical-induced luminescence. By studying three types of physically-linked DN gels with and without different crosslinkers, the PI's group expects to reveal some fundamental principles about the intrinsic structure-property relationships amongst structural network topologies, functional interactions between and within two networks, and structural dependence on toughening, self-healing, and energy-dissipation mechanisms. To this end three tasks will be explored: The first task is to study the functional role of the first and second networks on mechanical properties of the physically-based DN gels and to understand how different networks and their interactions affect observable mechanical properties. The second task centers on the study of the self-recovery and self-healing properties and mechanisms of the DN gels while still retaining good mechanical properties. In parallel to the experimental tasks, computational components will include the study of structure, dynamics, and interactions between the two networks and crosslinkers. Moreover, a theoretical model will be developed to describe the dependence of networks on mechanical, self-recovery/healing properties, and energy dissipation. Combination and comparison of the computational and experimental results will help to establish a relationship between the macroscopic performance of the physically-linked DN gels and the nanoscopic network interactions at different time-scales and length-scales, eventually aiming to develop a set of rules for rational design of new tough gels.