The Kirkwood-Riseman Polymer Model of Polymer Dynamics is Qualitatively Correct

TL;DR

This study uses Brownian dynamics simulations to compare the Kirkwood-Riseman and Rouse models of polymer dynamics in shear flow, demonstrating that the Kirkwood-Riseman model accurately predicts polymer rotation while the Rouse model does not.

Contribution

The paper provides evidence that the Kirkwood-Riseman model correctly describes polymer rotation in shear flow, unlike the Rouse model, which is invalid under these conditions.

Findings

Polymer coils rotate in shear flow as per Kirkwood-Riseman model.

Rouse modes are cross-correlated and affected by shear rate.

Rouse's calculation is only valid in quiescent fluids, not shear flow.

Abstract

We use Brownian dynamics to show: For an isolated polymer coil in a shear field, the Kirkwood-Riseman model for chain motion is qualitatively correct. Under the same circumstances the Rouse model for chain motion is qualitatively incorrect. The models are qualitatively different. Kirkwood and Riseman say polymer coils in a shear field perform whole-body rotation; in the Rouse model rotation does not occur. Our simulations demonstrate that \emph{in shear flow}: Polymer coils rotate. Rouse modes are cross-correlated. The amplitudes and relaxation rates of Rouse modes depend on the shear rate. Rouse's calculation only refers to a polymer coil in a quiescent fluid, where there is no viscous dissipation. Application of the Rouse model to a polymer coil undergoing shear is invalid.