Scaling Behavior of Anisotropy Relaxation in Deformed Polymers

Lam, Christopher N.; Xu, Wensheng; Chen, Wei‐Ren; Wang, Zhe; Stanley, Christopher B.; Carrillo, Jan‐Michael Y.; Uhrig, David; Wang, Weiyu; Hong, Kunlun; Porcar, Lionel; Do, Changwoo; Smith, Gregory S.; Sumpter, Bobby G.; Wang, Yangyang

doi:10.1103/physrevlett.121.117801

Cited by 16 publications

(28 citation statements)

References 51 publications

(47 reference statements)

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“…We presented results for the wave vector dependence of a spherical harmonic of the structure factor S 2 0 that has been measured in recent experiments. 23,58 The decay of the minimum of S 2 0 was found to be directly proportional to the decay in the mean nematic order of chains at the end−end scale. This correspondence will prove useful in interpreting future experiments.…”

Section: ■ Conclusionmentioning

confidence: 94%

Stress Relaxation in Highly Oriented Melts of Entangled Polymers

2019

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Molecular dynamics simulations are used to study relaxation of entangled polymer melts deformed far from equilibrium by uniaxial extensional flow. Melts are elongated to a Hencky strain of 6 at Rouse–Weissenberg numbers from 0.16 to 25, producing states with a wide range of chain alignment. Then flow is ceased and the systems are allowed to relax until twice the equilibrium disentanglement time. The relaxation of the stress is correlated with changes in the conformation of chains and the geometry of the tube confining them. Independent of initial alignment, chains relax to conformations consistent with the equilibrium tube length and diameter on the equilibrium Rouse time. Subsequent relaxation is the same for all systems and controlled by the equilibrium distentanglement time. These results are counter to recent work that suggests orientation causes a large, stretch-dependent reduction in the entanglement density that can only be recovered slowly by reptation on the equilibrium disentanglement time, raising fundamental questions about the nature of entanglement in aligned polymer melts.

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Section: ■ Conclusionmentioning

confidence: 94%

Stress Relaxation in Highly Oriented Melts of Entangled Polymers

2019

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“…While a chain length of 120 beads is somewhat above the entanglement length, which is reported to be about 84 in a similar coarse-grained polymer melt with purely repulsive nonbonded interactions at a number density of ρ = 0.85σ –3 and a temperature of T = 1.0ε/ k B , entanglement effects on segmental dynamics are expected to be small or negligible in our polymer model. In previous works, , a melt with a chain length of 120 beads was utilized to study the characteristic linear and nonlinear dynamics of unentangled polymer melts at ρ = 0.85σ –3 and T = 1.0ε/ k B . We use the model with 120 beads here to explore the glass formation of polymer melts in a mass range where the segmental dynamics should be insensitive to chain length.…”

Section: Model and Simulation Detailsmentioning

confidence: 99%

Investigation of the Temperature Dependence of Activation Volume in Glass-Forming Polymer Melts under Variable Pressure Conditions

Douglas

Xia

et al. 2020

Macromolecules

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Motivated by empirical observations suggesting that changes in the activation volume ΔV # upon varying temperature (T), determined from the pressure (P) dependence of the segmental structural relaxation time τ α , might be related to changes in the extent of collective motion in glass-forming liquids, we investigate the temperature dependence of ΔV # and the extent of collective motion in a coarse-grained polymer melt using molecular dynamics simulation. After confirming the validity of the string model of the dynamics of glass-forming liquids in predicting the T and P dependence of τ α , we find that there is unfortunately no direct relation between ΔV # and the average string length L quantifying the extent of collective motion. This negative finding is also in qualitative accord with predictions from the generalized entropy theory of glass formation, in which the extent of collective motion is quantified indirectly through the configurational entropy of polymer melts. By drawing an analogy between the definitions of ΔV # and the fragility of glass formation, we instead find that both ΔV # and fragility are complex quantities involving a convolution of energetic effects associated with the variation of activation free energy, along with changes in the extent of collective motion with T and P. We further demonstrate that the extent of collective motion can be estimated quantitatively by normalizing the activation free energy by its value at the onset temperature of glass formation. It is suggested that this normalized measure of the change of collective motion with T should be superior to fragility in quantifying the role of collective motion in condensed materials giving rise to non-Arrhenius relaxation.

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“…To complement the molecular dynamics simulations of the semi-flexible chain model, we further consider a fully flexible bead-spring model [12,[27][28][29]. In this model, the pair interactions between any two beads are described by the WCA potential, i.e., the repulsive part of the Lennard-Jones potential [Eq.…”

Section: Fully Flexible Chain Modelmentioning

confidence: 99%

Spatial correlations of entangled polymer dynamics

Ma,

Carrillo,

et al. 2021

Preprint

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The spatial correlations of entangled polymer dynamics are examined by molecular dynamics simulations and neutron spin-echo spectroscopy. Due to the soft nature of topological constraints, the initial spatial decays of intermediate scattering functions of entangled chains are, to the first approximation, surprisingly similar to those of an unentangled system in the functional forms. However, entanglements reveal themselves as a long tail in the reciprocal-space correlations, implying a weak but persistent dynamic localization in real space. Comparison with a number of existing theoretical models of entangled polymers suggests that they cannot fully describe the spatial correlations revealed by simulations and experiments. In particular, the strict one-dimensional diffusion idea of the original tube model is shown to be flawed. The dynamic spatial correlation analysis demonstrated in this work provides a useful tool for interrogating the dynamics of entangled polymers. Lastly, the failure of the investigated models to even qualitatively predict the spatial correlations of collective single-chain density fluctuations points to a possible critical role of incompressibility in polymer melt dynamics.

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Scaling Behavior of Anisotropy Relaxation in Deformed Polymers

Cited by 16 publications

References 51 publications

Stress Relaxation in Highly Oriented Melts of Entangled Polymers

Stress Relaxation in Highly Oriented Melts of Entangled Polymers

Investigation of the Temperature Dependence of Activation Volume in Glass-Forming Polymer Melts under Variable Pressure Conditions

Spatial correlations of entangled polymer dynamics

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