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

Published on Nov 25, 2019in Macromolecules5.985
· DOI :10.1021/ACS.MACROMOL.9B00901
Weizhong Zou5
Estimated H-index: 5
(UM: University of Michigan),
Soroush Moghadam3
Estimated H-index: 3
(UM: University of Michigan)
+ 1 AuthorsRonald G. Larson88
Estimated H-index: 88
(UM: University of Michigan)
Sources
Abstract
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 ...
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1 Author (Hendrik Meyer)
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We carried out a large set of tests to establish a correlation between the molecular (network) structure (influenced by molecular weight, molecular weight distribution, and melt predeformation) and mechanical responses of several glassy polymers to uniaxial compression at different temperatures and different compression speeds. The experimental results show that to have ductile responses there must be an adequate chain network, afforded by the interchain uncrossability among sufficiently long ch...
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The traditional Doi–Edwards tube model, applied to extensional flows at strain rates above the inverse Rouse time, predicts that the tube deforms affinely, which implies that the extensional stress reaches its plateau as soon as the chain has become locally fully stretched, even if the chain is still folded, and far from being completely unraveled. By starting from a state in which the chain is in a locally fully stretched, but folded, state, we develop an “entangled kink dynamics algorithm” tha...
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