Swollen elastomer networks are polymeric materials that have the potential to play key roles in advancing of a number of health, energy, and environmental applications. These include biological soft-tissue replacement materials such as those found in the meniscus of the knee or the intervertebral disc of the spine, separation membranes for selective removal of chemical or biological contaminants, durable and rapid ion-transport membranes for battery technology, and materials designed to provide long-term impact protection (military, athletics) while retaining high elastic flexibility. Reduction to practice, however, has been plagued by materials with limited ability to meet the mechanical demands required of such applications, being subject to rapid decay in elasticity and susceptibility to failure by fracture. This project is focused on using a new paradigm in swollen elastomer network design to create mechanically robust polymers capable of sustaining repetitive stress dissipation without fatigue while suppressing susceptibility to fracture and failure needed to ensure long-term performance. The scientific advancement efforts in the project will be integrated with interdisciplinary education of students. It will also be accompanied by development of workshops aimed at building collaborations among top soft-matter synthesis and mechanics groups around the world, in an effort to push the frontiers of science, explore new ideas, and accelerate the untapped potential of these unique polymeric materials. The workshops importantly will provide a forum to encourage talented, yet underrepresented young researchers, and provide them access to and mentorship from leading materials researchers in the world.
PART 2: TECHNICAL SUMMARY
Creative efforts in polymer network design over the last decade have led to numerous impactful improvements in hydrogel mechanics. Notable examples include both highly elastic hydrogel networks in which fatigue is minimal but very little energy is dissipated, and highly dissipative hydrogel networks in which toughness is maximized but fatigue is rapid and recovery is subject to long recovery times (minutes to days). Effective integration of both dissipative capabilities and efficient elastic recovery, however, appears limited using current design strategies. The principal objective of this proposal is to demonstrate the ability of junction point morphology (nanostructure) and strand-level organizational control to maximize non-plastic energy dissipation, recovery rate, and fatigue resistance simultaneously in swollen polymer networks. The central hypothesis of the proposed research is that synthetic integration of non-bond rupturing dissipative interactions into every molecular strand of the network, combined with implicit coupling of the dissipation mechanism to its own driving force for elastic recovery, will add substantial dissipative capability without sacrificing the rapid elastic recovery or the exceptional fatigue resistance. The project involves the synthetic development of uniquely designed ABC and ABCBA block copolymers which upon heating self-assemble into highly efficient network structures based on core-shell sphere morphologies. The objectives are to explore the ability of the B block domain size and degree of hydrophobicity to successfully tune the magnitude of dissipated energy (e.g., through measurement of fracture toughness) and understand its dependence on strain and strain rate. If successful, this project will transform our access to hydrogel materials that exhibit both fatigue resistance and toughness (bulk and fracture), at rates of recovery far exceeding the most advanced hydrogel systems developed to date.
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.
