Rheologica Acta

, Volume 46, Issue 9, pp 1171–1186 | Cite as

A molecular dynamics study of the stress–optical behavior of a linear short-chain polyethylene melt under shear

  • Chunggi Baig
  • Brian J. Edwards
  • David J. Keffer
Original Contribution


In this study, we present details of the stress–optical behavior of a linear polyethylene melt under shear using a realistic potential model. We demonstrate the existence of the critical shear stress, above which the stress–optical rule (SOR) begins to be invalid. The critical shear stress of the SOR of this melt turns out to be 5.5 MPa, which is fairly higher than 3.2 MPa at which shear thinning starts, indicating that the SOR is valid up to a point well beyond the incipient point of shear thinning. Furthermore, contrary to conventional wisdom, the breakdown of the SOR turns out not to be correlated with the saturation of chain extension and orientation: It occurs at shear rates well before maximum chain extension is obtained. In addition to the stress and birefringence tensors, we also compare two important coarse-grained second-rank tensors, the conformation and orientation tensors. The birefringence, conformation, and orientation tensors display nonlinear relationships to each other at high values of the shear stress, and the deviation from linearity begins at approximately the critical shear stress for breakdown of the SOR.


Birefringence Stress–optical rule Shear Nonequilibrium molecular dynamics Linear polyethylene melt 



This research used resources of the Center for Computational Sciences at Oak Ridge National Laboratory, through the University of Tennessee Computational Sciences Initiative. Additional support for CB was provided by the University of Tennessee Computational Sciences Initiative. ORNL is operated for the DOE by UT-Battelle, LLC, under contract number DE-AC0500OR22725.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Chunggi Baig
    • 1
  • Brian J. Edwards
    • 1
  • David J. Keffer
    • 1
  1. 1.Department of Chemical EngineeringUniversity of TennesseeKnoxvilleUSA

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