(589f) Time?Temperature Superposition for Integration of Atomistic Simulations with Experiment for Thermomechanical Properties of Cross-Linked Epoxy

An inalienable aspect of the thermomechanical behavior of viscoelastic materials such as cross-linked epoxy is the time dependence of their response to perturbations such as temperature change or strain. As a result of the vast mismatch in accessible time scales between atomistic simulations and typical experiments, such time dependence makes the prospect of the quantitative comparison of results from the two methods nebulous. Here, we show that the time-temperature superposition principle can be leveraged for analyzing the trends of specific volume and dynamics (both translational and orientational) obtained using atomistic simulations. The resulting analysis shows that atomistic simulations quantitatively capture the molecular mechanism underlying the viscoelasticity of the cross-linked epoxy network. Specifically, the temporal features of master curves of dynamic properties obtained from atomistic simulations can be quantitatively compared with the trend in experimental creep compliance. Further, we show that the details of the molecular topology have an impact on the dynamics of the atoms, which then will have an impact on the behavior of the molecular probes (mechanophores) using for metrology by our experimental collaborators. While our application is specific to cross-linked epoxy, the methods developed in our work are general and should in principle be applicable to other viscoelastic materials. Our results suggest that time-temperature superposition, which has proved invaluable in polymer rheology for many decades, can now be an important tool for integrating molecular length and time scale insight from atomistic simulations with experiments at typical scales relevant for commercial applications.