Viscoelasticity and self-healing property of dynamic covalent polymers: A molecular dynamics simulation

In this work, a coarse-grained model of dynamic covalent polymers (DCP) based on dynamic covalent bonds (DCBs) is first constructed. Then, the dynamics of DCBs is characterized by analyzing the time correlation function where lifetime exhibits an Arrhenius dependence on temperature. Following it, the viscoelasticity of DCP is explored by tuning the number of DCBs and temperature. The storage modulus exhibits a significant decrease at the critical shear strain amplitude (γ₀) while the loss modulus reaches the maximum value. This is because of the orientation and stretching of chains as a function of the shear strain amplitude. The decrease magnitude in the storage modulus rises with increasing the number of DCBs. This can be understood well by characterizing the number, lifetime, bond length distribution of DCBs, and bond energy per DCBs at the critical γ₀. Furthermore, both the storage modulus and loss modulus decrease with increasing the temperature. This is because the number and lifetime of DCBs are reduced with increasing the temperature while the bond energy per DCBs is improved. Interestingly, the maximum loss modulus peak at the critical γ₀ gradually disappears with reducing the temperature. Finally, the self-healing process is quantitatively simulated by analyzing the self-healing degree. The relationship between the characteristic self-healing time and the self-healing temperature follows an Arrhenius behavior. In summary, this work presents a new understanding on the effect of DCBs on the viscoelasticity and self-healing property of DCP at the molecular scale.