Reentrant transition in the shear viscosity of dilute rigid rod dispersions

TL;DR

This study uses direct numerical simulations to investigate the shear viscosity behavior of dilute rigid rod dispersions, revealing a reentrant transition from shear-thinning to Newtonian behavior around a specific Peclet number, with detailed analysis of underlying mechanisms.

Contribution

It introduces a DNS method to accurately reproduce the reentrant shear viscosity transition and confirms the theoretical Peclet number prediction for the dynamical crossover.

Findings

Reentrant transition from shear-thinning to Newtonian regime at Pe≈150.

Viscosity undershoot observed before reaching the 2nd Newtonian regime.

Good agreement between DNS results and theoretical predictions.

Abstract

The intrinsic viscosity of a dilute dispersion of rigid rods is studied using a recently developed direct numerical simulation (DNS) method for particle dispersions. A reentrant transition from shear-thinning to the 2nd Newtonian regime is successfully reproduced in the present DNS results around a Peclet number ${\rm Pe}=150$, which is in good agreement with our theoretical prediction of ${\rm Pe}=143$, at which the dynamical crossover from Brownian to non-Brownian behavior takes place in the rotational motion of the rotating rod. The viscosity undershoot is observed in our simulations before reaching the 2nd Newtonian regime. The physical mechanisms behind these behaviors are analyzed in detail.