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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.
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Nonsteady fracture of transient networks: The case of vitrimer
We have discovered a peculiar form of fracture that occurs in polymer network formed by covalent adaptable bonds. Due to the dynamic feature of the bonds, fracture of this network is rate dependent, and the crack propagates in a highly nonsteady manner. These phenomena cannot be explained by the existing fracture theories, most of which are based on steady-state assumption. To explain these peculiar characteristics, we first revisit the fundamental difference between the transient network and the covalent network in which we highlighted the transient feature of the cracks. We extend the current fracture criterion for crack initiation to a time-evolution scheme that allows one to track the nonsteady propagation of a crack. Through a combined experimental modeling effort, we show that fracture in transient networks is governed by two parameters: the Weissenberg number W 0 that defines the history path of crack-driving force and an extension parameter Z that tells how far a crack can grow. We further use our understanding to explain the peculiar experimental observation. To further leverage on this understanding, we show that one can “program” a specimen’s crack extension dynamics by tuning the loading history.
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- Award ID(s):
- 1761918
- PAR ID:
- 10295771
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 118
- Issue:
- 29
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- e2105974118
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1073/pnas.2105974118
