Nonequilibrium molecular dynamics study of ring polymer melts under shear and elongation flows: A comparison with their linear analogs
Abstract
We present detailed results for the structural and rheological properties of unknotted and unconcatenated ring polyethylene (PE) melts under shear and elongation flows via direct atomistic nonequilibrium molecular dynamics simulations. Short (C{sub 78}H{sub 156}) and long (C{sub 400}H{sub 800}) ring PE melts were subjected to planar Couette flow (PCF) and planar elongational flow (PEF) across a wide range of strain rates from linear to highly nonlinear flow regimes. The results are analyzed in detail through a direct comparison with those of the corresponding linear polymers. We found that, in comparison to their linear analogs, ring melts possess rather compact chain structures at or near the equilibrium state and exhibit a considerably lesser degree of structural deformation with respect to the applied flow strength under both PCF and PEF. The large structural resistance of ring polymers against an external flow field is attributed to the intrinsic closedloop configuration of the ring and the topological constraint of nonconcatenation between ring chains in the melt. As a result, there appears to be a substantial discrepancy between ring and linear systems in terms of their structural and rheological properties such as chain orientation, the distribution of chain dimensions, viscosity, flow birefringence, hydrostatic pressure, themore »
 Authors:
 Department of Chemical Engineering, School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689798 (Korea, Republic of)
 Publication Date:
 OSTI Identifier:
 22598952
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Journal of Rheology; Journal Volume: 60; Journal Issue: 4; Other Information: (c) 2016 The Society of Rheology; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; BIREFRINGENCE; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; CORRELATION FUNCTIONS; COUETTE FLOW; ELONGATION; LIMITING VALUES; MOLECULAR DYNAMICS METHOD; NONLINEAR PROBLEMS; POLYETHYLENES; RINGS; SHEAR; STRAIN RATE; TOPOLOGY; VISCOSITY
Citation Formats
Yoon, Jeongha, Kim, Jinseong, and Baig, Chunggi, Email: cbaig@unist.ac.kr. Nonequilibrium molecular dynamics study of ring polymer melts under shear and elongation flows: A comparison with their linear analogs. United States: N. p., 2016.
Web. doi:10.1122/1.4954246.
Yoon, Jeongha, Kim, Jinseong, & Baig, Chunggi, Email: cbaig@unist.ac.kr. Nonequilibrium molecular dynamics study of ring polymer melts under shear and elongation flows: A comparison with their linear analogs. United States. doi:10.1122/1.4954246.
Yoon, Jeongha, Kim, Jinseong, and Baig, Chunggi, Email: cbaig@unist.ac.kr. 2016.
"Nonequilibrium molecular dynamics study of ring polymer melts under shear and elongation flows: A comparison with their linear analogs". United States.
doi:10.1122/1.4954246.
@article{osti_22598952,
title = {Nonequilibrium molecular dynamics study of ring polymer melts under shear and elongation flows: A comparison with their linear analogs},
author = {Yoon, Jeongha and Kim, Jinseong and Baig, Chunggi, Email: cbaig@unist.ac.kr},
abstractNote = {We present detailed results for the structural and rheological properties of unknotted and unconcatenated ring polyethylene (PE) melts under shear and elongation flows via direct atomistic nonequilibrium molecular dynamics simulations. Short (C{sub 78}H{sub 156}) and long (C{sub 400}H{sub 800}) ring PE melts were subjected to planar Couette flow (PCF) and planar elongational flow (PEF) across a wide range of strain rates from linear to highly nonlinear flow regimes. The results are analyzed in detail through a direct comparison with those of the corresponding linear polymers. We found that, in comparison to their linear analogs, ring melts possess rather compact chain structures at or near the equilibrium state and exhibit a considerably lesser degree of structural deformation with respect to the applied flow strength under both PCF and PEF. The large structural resistance of ring polymers against an external flow field is attributed to the intrinsic closedloop configuration of the ring and the topological constraint of nonconcatenation between ring chains in the melt. As a result, there appears to be a substantial discrepancy between ring and linear systems in terms of their structural and rheological properties such as chain orientation, the distribution of chain dimensions, viscosity, flow birefringence, hydrostatic pressure, the pair correlation function, and potential interaction energies. The findings and conclusions drawn in this work would be a useful guide in future exploration of the characteristic dynamical and relaxation mechanisms of ring polymers in bulk or confined systems under flowing conditions.},
doi = {10.1122/1.4954246},
journal = {Journal of Rheology},
number = 4,
volume = 60,
place = {United States},
year = 2016,
month = 7
}

Nonequilibrium molecular dynamics simulations have been performed in order to compare the characteristics of planar Couette, planar elongation, uniaxial stretching, and biaxial stretching flows in simple fluids at different strain rates. After deriving the periodic boundary conditions for general flow fields and introducing some methodological improvements for elongation flow calculations we simulated the combination of shear and shearfree flows as well. We found that even at high strain rates where simple fluids exhibit strong nonNewtonian behavior (shearthinning) it is a reasonable approximation to consider the two planar flows to be rotationally equivalent. This is because in planar Couette flow themore »

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