Emergent Mechanics of Dynamic Polymer Network: Viscoelasticity, Damage, and Remodeling.*

A large majority of soft biological materials are made of elastic molecular networks with changing topology, allowing to accommodate growth, remodeling, and self-healing over time. Such behaviors can now be replicated in man-made polymers through the synthesis of networks whose chains are connected by weak molecular bonds, which under thermal fluctuations can permanently associate and dissociate. In contrast to their elastic counterparts, these networks therefore exhibit a myriad of new physics (flow, elastic deformation, self-healing, programmability, actuation, ...) that can be controlled by network topology, bond dynamics, and deformation rate. With these opportunities come challenges, related to a steep increase in the design space, but also is our ability to understand how these spatio-temporal network give rise to more and more complex macroscopic response. The presentation will tackle this challenge by providing an overview of the inner workings of these networks together with ways to characterize their response using concepts in statistical mechanics and the dynamics of complex systems. We will first discuss how a simple dynamic network can transition from a viscous fluid to an elastic solid and are able to remodel their structure and relax stresses over time. Based on this, we will turn to the behavior of these networks under damage, fracture and self-healing with a particular attention to the development of cavitation. These concepts will be used to illustrate the puzzling response of various dynamics networks, ranging from the nonlinear rheological behavior of fire-ant aggregations to the transient fracture of vitrimers, a new class of dynamic polymers. We will finally take inspiration from biological dynamic networks to explore how a new generation of living polymers can be developed to create well-controlled active and smart soft materials