Simple Model for the Deformation-Induced Relaxation of Glassy Polymers

Fielding, Suzanne M.; Larson, Ronald G.; Cates, Michael E.

doi:10.1103/physrevlett.108.048301

Cited by 37 publications

(61 citation statements)

References 37 publications

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“…(Figure 1 shows all these features for a theoretical curve that was presented in Ref. 23 as the best fit to the data of Lee et al; the unloading part is discussed separately below.) The rise in τ (t) happens as the local strain rate starts to drop: the latter property defines onset of the so-called strain-hardening regime.…”

Section: Strain Hardeningmentioning

confidence: 99%

“…However, it should be possible to do this with relatively simple fluidity-inspired modifications to the EGP model, and indeed the work begun in Ref. 23 and continued in this paper could be interpreted as a step in exactly that direction. Meanwhile though, the EGP's precepts as currently formulated are arguably unsuited to the regime of strong fluidization arising just below T g that was addressed experimentally in Ref.…”

Section: Strain Hardeningmentioning

confidence: 99%

“…(As explained in Ref. 23, the numerical solver introduces, in lieu of inertia, a small additional fluid viscosity η n = 0.05G p τ 0 into Eq. (1), whose magnitude has negligible influence on these plots.…”

Section: Strain Hardeningmentioning

confidence: 99%

“…This renewed approach was initiated by three of us in Ref. 23, mainly within the specific context of explaining strain hardening under tensile loading, and its effects on segmental relaxation rates, as observed in Ref. 8.…”

Section: Introductionmentioning

confidence: 99%

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Modeling the relaxation of polymer glasses under shear and elongational loads

Fielding

Moorcroft

Larson

et al. 2013

The Journal of Chemical Physics

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Glassy polymers show "strain hardening": at constant extensional load, their flow first accelerates, then arrests. Recent experiments under such loading have found this to be accompanied by a striking dip in the segmental relaxation time. This can be explained by a minimal nonfactorable model combining flow-induced melting of a glass with the buildup of stress carried by strained polymers. Within this model, liquefaction of segmental motion permits strong flow that creates polymer-borne stress, slowing the deformation enough for the segmental (or solvent) modes then to re-vitrify. Here, we present new results for the corresponding behavior under step-stress shear loading, to which very similar physics applies. To explain the unloading behavior in the extensional case requires introduction of a "crinkle factor" describing a rapid loss of segmental ordering. We discuss in more detail here the physics of this, which we argue involves non-entropic contributions to the polymer stress, and which might lead to some important differences between shear and elongation. We also discuss some fundamental and possibly testable issues concerning the physical meaning of entropic elasticity in vitrified polymers. Finally, we present new results for the startup of steady shear flow, addressing the possible role of transient shear banding.

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Section: Strain Hardeningmentioning

confidence: 99%

Section: Strain Hardeningmentioning

confidence: 99%

Section: Strain Hardeningmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling the relaxation of polymer glasses under shear and elongational loads

Fielding

Moorcroft

Larson

et al. 2013

The Journal of Chemical Physics

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“…15(b)] during this early-time regime before the resulting polymeric contribution to the stress becomes comparable with solvent and nematic stresses, which are O(1) in our units. (A comparable phenomenon is seen in some models of polymeric glasses [69]. )…”

Section: B Elastomeric Active Mattermentioning

confidence: 61%

Viscoelastic and elastomeric active matter: Linear instability and nonlinear dynamics

2016

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Publisher's copyright statement:Reprinted with permission from the American Physical Society: Physical Review E 93, 032702 c (2016) by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modi ed, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We consider a continuum model of active viscoelastic matter, whereby an active nematic liquid crystal is coupled to a minimal model of polymer dynamics with a viscoelastic relaxation time τ C . To explore the resulting interplay between active and polymeric dynamics, we first generalize a linear stability analysis (from earlier studies without polymer) to derive criteria for the onset of spontaneous heterogeneous flows (strain rate) and/or deformations (strain). We find two modes of instability. The first is a viscous mode, associated with strain rate perturbations. It dominates for relatively small values of τ C and is a simple generalization of the instability known previously without polymer. The second is an elastomeric mode, associated with strain perturbations, which dominates at large τ C and persists even as τ C → ∞. We explore the dynamical states to which these instabilities lead by means of direct numerical simulations. These reveal oscillatory shear-banded states in one dimension and activity-driven turbulence in two dimensions even in the elastomeric limit τ C → ∞. Adding polymer can also have calming effects, increasing the net throughput of spontaneous flow along a channel in a type of drag reduction. The effect of including strong antagonistic coupling between the nematic and polymer is examined numerically, revealing a rich array of spontaneously flowing states.

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Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

Bending

Ediger

2016

J Polym Sci B Polym Phys

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We performed constant strain rate deformation and stress relaxation on a poly(methyl methacrylate) glass at Tg – 19 K, utilizing three strain rates and initiating the stress relaxation over a large range of strain values. Following previous workers, we interpret the initial rate of decay of the stress during the relaxation experiment as a purely mechanical measure of mobility for the system. In our experiments, the mechanical mobility obtained in this manner changes by less than a factor of 3 prior to yield. During these mechanical experiments, we also performed an optical measurement of segmental mobility based on the reorientation of a molecular probe; we observe that the probe mobility increases up to a factor of 100 prior to yield. In the post‐yield regime, in contrast, the mobilities determined mechanically and by probe reorientation are quite similar and show a similar dependence on the strain rate. Dynamic heterogeneity is found to initially decrease during constant strain rate deformation and then remain constant in the post‐yield regime. These combined observations of mechanical mobility, probe mobility, and dynamic heterogeneity present a challenge for theoretical modeling of polymer glass deformation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1957–1967

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Simple Model for the Deformation-Induced Relaxation of Glassy Polymers

Cited by 37 publications

References 37 publications

Modeling the relaxation of polymer glasses under shear and elongational loads

Modeling the relaxation of polymer glasses under shear and elongational loads

Viscoelastic and elastomeric active matter: Linear instability and nonlinear dynamics

Comparison of mechanical and molecular measures of mobility during constant strain rate deformation of a PMMA glass

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