Network alteration of cyclically loaded elastomers mediated by dynamic bonds

Abstract

Elastomers and hydrogels with dynamic network structures have received considerable research interest due to their high strength and toughness, and self-healing ability. While the general mechanical responses of dynamic polymer networks have been investigated, the study on their fatigue behaviors is still in its infancy. In this work, we employ experimental and theoretical approaches to gain a comprehensive understanding of the mechanical response of an elastomer with physical crosslinkers under fatigue tests up to 10,000 cycles. The constitutive model characterizes the network configuration using the density distribution function of the polymer chains, which is represented by a state variable denoting the stress-free configuration of each individual chain. The model takes into account the reversible dissociation/association of dynamic bonding facilitated by the physical crosslinkers. As a result, polymer chains can repeatedly release the involved strain energy and transform between different stress-free configurations. A multi-dispersed reaction process is further employed to describe the state transition of polymer chains, enabling the model to elucidate the progressive damage in long-term relaxation and fatigue tests by recording and updating the density distribution function of chain state. In addition, the reversible transition of the polymer chain between different state configurations enables the model to capture the rate-dependent stress response and relaxation behaviors of physically crosslinked elastomers and gels. Remarkably, our microscopic model, which requires only five parameters, offers an efficient approach to describe the mechanical responses of elastomers and gels with dynamic bonds.