Prediction of viscoelastic properties with coarse-grained molecular dynamics and experimental validation for a benchmark polyurea system

To explore the relationship between microscopic structure and viscoelastic properties of polyurea, a coarse-grained (CG) model is developed by a structure matching method and validated against experiments conducted on a controlled, benchmark material. Using the Green-Kubo method, the relaxation function is computed from the autocorrelation of the stress tensor, sampled over equilibrium MD simulations, and mapped to a real time scale established by matching self-diffusion rates of atomistic and CG models. Master curves computed from the predicted stress relaxation function are then compared with dynamic mechanical analysis experiments mapped to a wide frequency range by time-temperature superposition, as well as measurements of ultrasonic shear wave propagation. Computational simulations from monodisperse and polydisperse configurations, representative of the benchmark polyurea, show excellent agreement with the experimental measurements over a multidecade range of loading frequency.