Direct observation of reptation at polymer interfaces

Russell, Thomas P.; Deline, V. R.; Dozier, W. D.; Felcher, G. P.; Agrawal, Gaurav; Wool, Richard P.; Mays, Jimmy W.

doi:10.1038/365235a0

Cited by 82 publications

(59 citation statements)

References 15 publications

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“…The predicted M and T-dependences of T, , of the new CM remains the same as the original CM according to eq 5, where n, appearing therein is now the initial constant coupling parameter before it starts to decrease due to the onset of LCM. The recognition of the importance of LC in the new CM brings it in harmony with earlier propositions [44-461, simulations [31-331 and conclusions made from recent experimental investigations [59] that motion of an entangled chain is more facile along the general directions defined by the LC. However, the chain motion in the new CM is governed by the general principle of contraint dynamics modified by LCM.…”

Section: Dilute Polyisoprene Probes In Polybutadiene Matricessupporting

confidence: 64%

General Applicability of the Coupling Model to Viscoelasticity of Polymers : from Local Segmental Motion to Terminal Flow

1996

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Abstract. We survey the important problems in polymer viscoelasticity that impede progress in this field. These problems manifest themselves as spectacular anomalies in the viscoetastic data that have been reproduced in different polymers and in different laboratories, but have largely been put aside for lack of explanation. Without solving these difficult problems, there can be no satisfactory understanding of the viscoelastic properties of polymers spanning across the local segmental motion, the glass-rubber softening dispersion, the rubbery plateau and the terminal dispersion. The coupling model, which has general applicablity to various relaxation mechanisms of polymers and beyond polymers, is able to resolve all these problems.

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Section: Dilute Polyisoprene Probes In Polybutadiene Matricessupporting

confidence: 64%

General Applicability of the Coupling Model to Viscoelasticity of Polymers : from Local Segmental Motion to Terminal Flow

1996

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“…10.1021/acs.macromol.5b00791 Macromolecules XXXX, XXX, XXX−XXX B exhibit tube dynamics reminiscent of their much higher molecular weight, more entangled counterparts.…”

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confidence: 98%

Relaxation Dynamics of Nanoparticle-Tethered Polymer Chains

2015

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Relaxation dynamics of nanoparticle-tethered cis-1,4-polyisoprene (PI) are investigated using dielectric spectroscopy and rheometry. A model system composed of polymer chains densely grafted to spherical SiO 2 nanoparticles to form self-suspended suspensions facilitates detailed studies of slow global chain and fast segmental mode dynamics under surface and geometrical confinementfrom experiments performed in bulk materials. We report that unentangled polymer molecules tethered to nanoparticles relax far more slowly than their tethered entangled counterparts. Specifically, at fixed grafting density we find, counterintuitively, that increasing the tethered polymer molecular weight up to values close to the entanglement molecular weight speeds up chain relaxation dynamics. Decreasing the polymer grafting density for a fixed molecular weight has the opposite effect: it dramatically slows down chain relaxation, increases interchain coupling, and leads to a transition in rheological response from simple fluid behavior to viscoelastic fluid behavior for tethered PI chains that are unentangled by conventional measures. Increasing the measurement temperature produces an even stronger elastic response and speeds up molecular relaxation at a rate that decreases with grafting density and molecular weight. These observations are discussed in terms of chain confinement driven by crowding between particles and by the existence of an entropic attractive force produced by the space-filling constraint on individual chains in a self-suspended material. Our results indicate that the entropic force between densely grafted polymer molecules couples motions of individual chains in an analogous manner to reversible cross-links in associating polymers. ■ INTRODUCTIONUnderstanding the behaviors of macromolecules tethered to rigid supports/fillers is a longstanding challenge in soft matter science. Movement of short, unentangled linear polymer chains tethered to a support can normally be described using models for Brownian motion of beads linked by harmonic springs, such as that proposed by Rouse, 1−3 with the added constraint that the bead tethered to the support cannot move. When the molecular weights of the tethered chains become long enough to allow individual molecules to entangle, reptation and armretraction dynamics 4−10 are expected to be overlaid with those associated with surface attachment. 11 Model polymers with long-chain branches, such as stars, H-polymers, combs, and pompoms, exhibit aspects of these dynamics, and the concepts of arm retraction, hierarchical relaxation, and branch point diffusion play crucial roles in understanding their overall rheological properties. 12−15 Dynamics of entangled polymers in a variety of branched architectures have been studied with diverse approaches, including NMR, 16−18 neutron scattering, 19−21 rheology, 16,18−22 dielectric spectroscopy, 18−21 and others. Among these techniques, dielectric spectroscopy is advantageous because a material can be interrogated in an undeformed state wi...

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“…Entanglements are not directly observable and experiments are usually restricted to post-analysis of fracture surfaces [13] or bulk scattering [8], which does not isolate the response of the failing region. In contrast, computer simulations provide full spatial resolution throughout the failure process, allowing macroscopic stresses to be directly related to molecular structure and dynamics.…”

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confidence: 99%