Contrary to thermosets, vitrimers adjust their topology upon heating without loss of network integrity. Here, the proposed simulation methodology utilizes coarse-grained molecular dynamics in conjunction with a Monte Carlo method to capture the network integrity and flowability of vitrimers at high temperatures. The model vitrimer shows two transition temperatures. In addition to the conventional glass transition temperature, the topology freezing temperature is detected from the volumetric and rheological data. In the glassy state, the mobility of the vitrimer and thermoset is identical, whereas increasing the temperature results in a diffusive behavior in the vitrimer. The rheological data capture the main feature of vitrimers, which is the terminal regime of the elastic modulus at low frequencies. The zero-shear viscosity of the model vitrimer follows an Arrhenius-like temperature dependence at temperatures above the topology freezing temperature. The horizontal shift factors obtained from collapsing the rheological data onto master curves also display the same temperature dependence. Simulations reveal that the lifetime of the exchangeable bonds determines the rheology and dynamics of these networks. When the rate of the deformation is higher than the rate of the bond exchange, the system behaves as a typical thermoset, while at lower rates, the vitrimer behaves as a viscous liquid.

We implement a hybrid molecular dynamics/Monte Carlo simulation to study the microscopic dynamics and the macroscopic rheology of vitrimers with a fast bond exchange rate. We show that the linear viscoelastic properties and mean squared displacement of the vitrimers collapse onto master curves by applying the same shift factors that follow the Williams−Landel−Ferry equation at low temperatures and Arrhenius-like behavior at high temperatures. The linkage between the microscopic dynamics and the linear rheology of vitrimers is established using the generalized Stokes−Einstein relationship, which efficiently extends the timescale of simulations and predicts the viscoelasticity. The values of the shift factors are related to the characteristic decay time of the intermediate scattering function, which is accessible in scattering experiments. The same results hold in the case of an all-atom model of an ionic liquid. Our methodology provides a microscopic basis for the time-superposition principle and predicts the macroscopic rheology of thermo-rheologically simple vitrimers.

Thermoset polymers are classified amongst the most challenging materials to recycle due to the permanent crosslinks that increase their strength and stiffness compared to their thermoplastic counterparts. Vitrimers provide a promising route to achieve the recyclability of thermosets by implementing dynamic covalent bonds within the network. In this study, a hybrid molecular dynamics (MD)‐Monte Carlo (MC) technique is used to simulate these adaptive networks constructed by a coarse‐grained model. The model proposed in this work describes the dynamic nature of the covalent bonds while maintaining a constant crosslink density. As this framework also shows flexibility in accommodating various exchange reaction activation energy via adjusting the energy difference in MC step, the dynamic and mechanical properties of the vitrimer system are intensely affected by the number of successful bond exchanges happening at every step. In both rubbery and glassy regimes, lowering the energy barrier of the bond exchange reaction results in enhanced motion for the vitrimer segments. This enhanced mobility, in turn, directly affects the stress–strain relationship of these networks, where a higher number of exchanges results in larger deformation before fracture even at low temperatures. Furthermore, the stress distribution in vitrimers shows more homogenous distribution before failure than in the thermoset network.

Vitrimers encompass the desirable mechanical properties of thermosets with the recyclability of thermoplastics. This ability arises from the rearrangement of the vitrimer covalent network upon heating via a bond shuffling mechanism while its cross‐link density remains preserved. This unique feature makes vitrimers interesting candidates for the design of materials that combine dimensional stability at high temperatures and solvent resistance with the ability to be reshaped and processed. Despite these advantages, vitrimer exhibits significant creep at operating conditions where thermosets show little or no creep. As the mechanical properties of vitrimers not only depend on their chemical composition but also on the dynamics of the polymer chains, molecular dynamics (MD) simulations can provide detailed molecular mechanisms of the system of interest under macroscopic stress‐induced deformations. In this regard, the recently developed MD/Monte Carlo simulation methodology capable of capturing the bond exchange mechanics in vitrimers is used to study the creep and recovery response of a coarse‐grained model thermoset and vitrimer with a fast bond exchange rate. The time‐stress superposition principle is then successfully applied to the creep response. The resulting universal curves enable us to predict the long‐time creep behavior of both systems extending the timescale from 4 to over 10 orders of magnitude.

All-atom molecular dynamics (MD) simulation is used to determine the thermodynamics and rheological properties of fuel surrogates, which are modeled as a mixture of n-hexadecane and methyl laurate. The volumetric properties of the studied systems, namely, density and coefficient of thermal expansion, show an excellent agreement with experiments. The temperature dependence of translational and rotational diffusion of the molecules follows an Arrhenius-type behavior, which is consistent with the temperature dependence of the zero shear viscosity obtained from nonequilibrium simulations. At high shear rates, the molecules align in the flow direction that gives rise to the shear-thinning behavior for these fuel surrogates. The time–temperature superposition (TTS) principle is then successfully applied to collapse the shear viscosity and translational/rotational motion data in all systems. The application of TTS on the dynamics data obtained in equilibrium, which are readily accessible in the all-atom MD simulations, allows one to reduce the time scale gap between experiments and simulations and predict the rheological response of complex fluids, especially mixtures of short alkanes and fatty acid esters, which are of interest in fuel surrogates.