Manipulating the Properties of Polymer Vitrimer Nanocomposites by Designing Dual Dynamic Covalent Bonds

Abstract

Polymer vitrimer is a novel material that contains dynamic covalent bonds (DCBs) allowing it to combine the desirable characteristics of both thermoplastics and thermosets. Similar to the traditional polymer nanocomposites, introducing nanoparticles into polymer vitrimer is also an effective strategy to further enhance its properties. However, a comprehensive understanding of matrix and interfacial bond exchange reactions (BERs) to tailor the properties of polymer vitrimer nanocomposites (PVNs) is still lacking. Herein, we utilized coarse-grained molecular dynamics simulations to investigate model PVNs in which there are two different kinds of DCBs in the vitrimer matrix and at the interface. Our results show that the normalized bond autocorrelation function (C_sw) confirms the independence of BERs in the vitrimer matrix and in the interface. By varying the bond swap energy barrier ($\Delta E_{\mathrm{sw}}$) in the matrix $\Delta E_{\mathrm{sw}}^{\mathrm{mat}}$ or in the interface $\Delta E_{\mathrm{sw}}^{\mathrm{int}}$, or in both $\Delta E_{\mathrm{sw}}^{\mathrm{all}}$, a maximum mechanical property is observed at the moderate value of $\Delta E_{\mathrm{sw}}^{\mathrm{mat}}$, $\Delta E_{\mathrm{sw}}^{\mathrm{int}}$, or$\Delta E_{\mathrm{sw}}^{\mathrm{all}}$. Meanwhile, the effect of $\Delta E_{\mathrm{sw}}$ on the stress relaxation and the bond orientation as a function of the time under a fixed strain is well probed, which both decay more slowly at greater $\Delta E_{\mathrm{sw}}$. We simulated the tension-recovery curve to examine the effect of $\Delta E_{\mathrm{sw}}$ on the hysteresis loss and permanent deformation of PVNs, finding an optimal value to achieve its minimum energy dissipation and maximum recovery ratio. Lastly, we investigated the efficiency of self-healing by building and removing walls from the system. Interestingly, a maximum self-healing efficiency of the stress-strain behavior is observed at moderate $\Delta E_{\mathrm{sw}}$. Overall, this study provides valuable insights into the relationship between the structure and properties of PVNs, offering implications for the manipulation of their mechanical properties and enhancement of their self-healing capabilities.