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Polymers 2017, 9(11), 556; https://doi.org/10.3390/polym9110556

Microstructural Origins of Nonlinear Response in Associating Polymers under Oscillatory Shear

1
Computational Materials and Data Science, Sandia National Laboratories, Albuquerque, NM 87123, USA
2
Department of Physics, San Diego State University, San Diego, CA 92182, USA
*
Author to whom correspondence should be addressed.
Received: 29 June 2017 / Revised: 22 October 2017 / Accepted: 24 October 2017 / Published: 26 October 2017
(This article belongs to the Special Issue Complex Fluid Rheology)
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Abstract

The response of associating polymers with oscillatory shear is studied through large-scale simulations. A hybrid molecular dynamics (MD), Monte Carlo (MC) algorithm is employed. Polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. Stress-strain curves show nonlinearities indicated by a non-ellipsoidal shape. We consider two types of nonlinearities. Type I occurs at a strain amplitude much larger than one, type II at a frequency at which the elastic storage modulus dominates the viscous loss modulus. In this last case, the network topology resembles that of the system at rest. The reversible bonds are broken and chains stretch when the system moves away from the zero-strain position. For type I, the chains relax and the number of reversible bonds peaks when the system is near an extreme of the motion. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups. Even though major restructuring occurs, the system remembers previous network topologies. View Full-Text
Keywords: associating polymers; oscillatory shear; MD/MC simulations; nonlinear response associating polymers; oscillatory shear; MD/MC simulations; nonlinear response
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Wilson, M.A.; Baljon, A.R.C. Microstructural Origins of Nonlinear Response in Associating Polymers under Oscillatory Shear. Polymers 2017, 9, 556.

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