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Issue 14, 2016
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Finite cohesion due to chain entanglement in polymer melts

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Abstract

Three different types of experiments, quiescent stress relaxation, delayed rate-switching during stress relaxation, and elastic recovery after step strain, are carried out in this work to elucidate the existence of a finite cohesion barrier against free chain retraction in entangled polymers. Our experiments show that there is little hastened stress relaxation from step-wise shear up to γ = 0.7 and step-wise extension up to the stretching ratio λ = 1.5 at any time before or after the Rouse time. In contrast, a noticeable stress drop stemming from the built-in barrier-free chain retraction is predicted using the GLaMM model. In other words, the experiment reveals a threshold magnitude of step-wise deformation below which the stress relaxation follows identical dynamics whereas the GLaMM or Doi–Edwards model indicates a monotonic acceleration of the stress relaxation dynamics as a function of the magnitude of the step-wise deformation. Furthermore, a sudden application of startup extension during different stages of stress relaxation after a step-wise extension, i.e. the delayed rate-switching experiment, shows that the geometric condensation of entanglement strands in the cross-sectional area survives beyond the reptation time τd that is over 100 times the Rouse time τR. Our results point to the existence of a cohesion barrier that can prevent free chain retraction upon moderate deformation in well-entangled polymer melts.

Graphical abstract: Finite cohesion due to chain entanglement in polymer melts

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Article information


Submitted
19 Jan 2016
Accepted
19 Feb 2016
First published
22 Feb 2016

Soft Matter, 2016,12, 3340-3351
Article type
Paper
Author version available

Finite cohesion due to chain entanglement in polymer melts

S. Cheng, Y. Lu, G. Liu and S. Wang, Soft Matter, 2016, 12, 3340
DOI: 10.1039/C6SM00142D

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