Primitive chain network simulations for double peaks in shear stress under fast flows of bidisperse entangled polymers

TL;DR

This study uses multi-chain slip-link simulations based on the primitive chain network model to analyze the molecular origins of double peaks in shear stress observed in bimodal entangled polymer blends under fast flows.

Contribution

It introduces a detailed simulation approach to decompose shear stress contributions and elucidate the molecular mechanisms behind double peaks in shear stress.

Findings

Double peaks correspond to short-chain orientation and long-chain stretch.

Peak positions are unaffected by chain mixing, but peak intensity depends on mixing conditions.

Simulation results agree with experimental data.

Abstract

A few experiments have reported that the time development of shear stress under fast start-up shear deformations exhibits double peaks before reaching the steady state for bimodal blends of entangled linear polymers in specific conditions. To analyze the molecular origin of this phenomenon, multi-chain slip-link simulations based on the primitive chain network model were conducted for the data of a bimodal polystyrene solution reported by Osaki et al. [J Pol Sci B Pol Phys, 38, 2043 (2000)] Owing to the reasonable agreement with the data and the simulation results, the stress was decomposed into contributions from long and short-chain components and decoupled into segment number, stretch, and orientation. The analysis revealed that the first and second peaks correspond to the short-chain orientation and the long-chain stretch, respectively. The results also imply that the peak positions are not affected by the mixing of short and long chains, whereas the second peak intensity depends on the mixing conditions in a complicated manner, dominating the emergence of double peaks.