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Multiscale Modeling of Sub-Entanglement-Scale Chain Stretching and Strain Hardening in Deformed Polymeric Glasses

Using both coarse-grained (CG) and fine-grained (FG) simulations we show how strain hardening in polymeric glasses under uniaxial extension arises from highly stretched strands that form as the polymer chains deform subaffinely on increasing length scales as strain increases. The coarse-grained simulations are performed using the hybrid Brownian dynamics method (HBD) [Zou, W.; Larson, R. G. Soft Matter 2016, 3, 3853–3865] with 10–30 coarse-grained springs per polymer chain, while the fine-grained simulations employ the Kremer-Grest bead–spring model with 600 beads per chain. We find that the HBD model accurately predicts how the MD chain configurations evolve during deformation despite being a single-chain-in-mean-field model that does not account for entanglements or monomer-level structure. We show using both models that the glassy strain hardening modulus GR is much larger than the melt plateau modulus GN because chain segments become highly stretched at modest Hencky strain (ϵ < ∼1) owing to the high ...