Molecular Understanding and Design of Physically-linked Double Network Hydrogels

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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.