Time-dependent constitutive behaviors of a dynamically crosslinked glycerogel governed by bond kinetics and chain diffusion

Soft materials featuring dynamic networks represent a burgeoning frontier in materials science, offering multifaceted applications spanning soft robotics, biomaterials, and flexible electronics. Unraveling the time-dependent constitutive behavior of these materials, rooted in dynamic networks, stands as a pivotal pursuit for engineering advancements. Herein, we fabricate a tough and extreme-temperature-tolerant glycerogel with a polymer network crosslinked by metal-coordination crosslinkers and conduct a thorough analysis of its intricate mechanical responses across monotonic loading, relaxation, creep, and cyclic tests. We then develop a physically grounded constitutive model integrating the dynamics of crosslinker association/dissociation and polymer chain diffusion, furnishing a holistic framework to elucidate their interplay. We employ a statistical description, using density functions of chains in terms of end-to-end vectors, to characterize network reconfiguration. The evolution of chain density under external load, mediated by crosslinker kinetics and chain diffusion in a viscous medium, leads to intriguing variations in elastic energy and stress responses. Through meticulous experimental validation and numerical simulations, we demonstrate the efficacy of the model in forecasting the mechanical behavior of dynamic polymer networks under diverse loading scenarios, encompassing strain rate effects, stress relaxation, Mullins effect, and self-recovery phenomena. Our findings provide valuable insights into the design and optimization of dynamic network-based materials for diverse applications in biomedical and engineering fields.