Individual Polymer Chain Dynamics in an Entangled Polymeric Liquid Using a Stochastic Tube Model

TL;DR

This paper uses a stochastic tube model to simulate and analyze the dynamics of individual polymer chains in entangled liquids under various shear and extension rates, revealing different rotational behaviors and elongation tendencies.

Contribution

It introduces new variables for analyzing chain linearity over time and clarifies polymer deformation mechanisms under shear and extension flows.

Findings

Polymer chains tend to elongate at higher shear rates.

Flipping rotations occur occasionally, especially at high shear.

No rotations observed under extensional flows.

Abstract

This study focuses on comparing the individual polymer chain dynamics in an entangled polymeric liquid under different shear and extension rates. Polymer chains under various shear rates and extension rates were simulated using a stochastic-tube model [J. Rheol. 56: 1057 (2012)]. We developed a Matlab code to visualize and analyze the simulated configurations from the stochastic-tube model. We introduced new variables to determine how the extent of linearity changes with time for different shear rates, which is more useful than a typical end-to-end distance analysis. We identified whether the polymer chains undergo a tumbling rotation (slight elongation not accompanying contraction) or flipping rotation (elongation accompanying contraction). The simulation results indicate that the polymer chains exhibit a significant tendency to elongate at higher shear rates and occasionally experience flipping, while lower shear rates tend to exhibit very frequent tumbling. Furthermore, no rotations were observed under extensional flows. These results help clarifying uncertainty of previously proposed polymer deformation mechanisms of the convective constraint release and the configuration-dependent friction coefficient.