Mechanics of CO2-induced dynamic covalent polymer networks: Constitutive modeling and crack healing

CO₂-induced dynamic covalent polymer networks (DCPNs) have received significant attention due to their capability of sequestering CO₂ to remodel material properties. Despite the promising success of carbon sequestration in the polymer, the mechanistic understanding of the CO₂-induced polymer network is still at the very beginning. A theoretical framework to understand the CO₂-induced formation of bulk networks and healing of interfacial cracks of DCPNs has not been established. Here, we build up a polymer-network-based theoretical model system that can mechanistically explain the constitutive behavior and crack healing of CO₂-induced DCPNs. We assume that the DCPN consists of interpenetrating networks crosslinked by CO₂-induced dynamic bonds which follow a force-dependent chemical kinetics. During the healing process, we consider the CO₂ molecules diffuse from the surface to the crack interface to reform the polymer network for interfacial repair. Our theoretical framework can calculate the stress-strain behaviors of both original and healed DCPNs. We demonstrate that the theoretically calculated stress-strain responses of the original DCPNs across various CO₂ concentrations, as well as those of healed DCPNs under different CO₂ concentrations, consistently match the documented experimental results. We expect our model to become an invaluable tool for innovating, designing, understanding, and optimizing CO₂-induced DCPNs.