Unveiling the Multiscale Dynamics of Polymer Vitrimers Via Molecular Dynamics Simulations

Abstract

The multiscale dynamical behaviors of reversible cross-linked networks (vitrimers) are investigated using coarse-grained molecular dynamics simulations, revealing that these behaviors have different dependencies on temperature and bond swap energy barriers. The simulation model displays significantly slower bond exchange rates compared with segmental relaxations. Short-time segmental scale mobility and relaxation are relatively unaffected by bond exchange, while whole-chain scale relaxation or long-time mobility is more constrained. Specifically, increasing the temperature reduces the dynamical heterogeneity and accelerates segmental relaxations, rendering the time− temperature superposition principles (TTSP) ineffective. The universal correlations between different dynamical behaviors of vitrimers, such as chain segmental relaxations, short-time vibration, and dynamical heterogeneity, are deduced. The comparable rates of chain length scale relaxation and bond exchange influence each other, leading to the breakdown of the TTSP and time-energy barrier superposition principles (TESP). By rational design, the bond exchange scale and whole chain relaxation scale can be tailored to become separated, which provides guidelines for the design of dynamic covalent or noncovalent polymer materials combining fast self-healing and good stability.

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

“…We utilize the harmonic potential function to simulate the bonding interactions in linear polymers, as illustrated below: U bond = 1 2 K false( r − r 0 false) 2 where K = 200ε/σ 2 is the bond strength constant, and r 0 = 1.0 is the equilibrium bond length, which can guarantee a certain stiffness of the bonds while avoiding high-frequency modes and chain crossing. ,, …”

“…where K = 200ε/σ 2 is the bond strength constant, and r 0 = 1.0 is the equilibrium bond length, which can guarantee a certain stiffness of the bonds while avoiding high-frequency modes and chain crossing. 32,36,39 All particles are placed in a large box with periodic boundary conditions. The velocity-Verlet algorithm is used to integrate the motion process, where the time step δt = 0.001τ.…”

Molecular Simulation of Covalent Adaptable Networks and Vitrimers: A Review

“…However, when modeling the bond exchange with a nonbonded Lennard-Jones potential, it is greatly influenced by thermal fluctuations or external forces [111]. Moreover, using the same model, the timetemperature superposition (TTSP) and time-energy barrier superposition (TESP) principles were investigated since both the bond swap energy barrier and the temperature were reported to have an effect on multiscale dynamics [112]. The dynamics involved were segmental dynamics, polymer bead mobility, polymer chain dynamics and bond swap dynamics.…”

“…The dynamics involved were segmental dynamics, polymer bead mobility, polymer chain dynamics and bond swap dynamics. TTSP was valid for polymer bead mobility and bond swap dynamics, and was valid for segmental dynamics and polymer chain dynamics only at low temperatures and low energy barriers, respectively [112]. TESP was only valid for segmental dynamics [112].…”

“…TTSP was valid for polymer bead mobility and bond swap dynamics, and was valid for segmental dynamics and polymer chain dynamics only at low temperatures and low energy barriers, respectively [112]. TESP was only valid for segmental dynamics [112]. Moreover, the scale of the different dynamical behaviors revealed that segmental dynamics were the fastest, followed by polymer bead mobility and polymer chain dynamics; bond swap dynamics were the slowest [112].…”