Orientational arrest in dense suspensions of elliptical particles under oscillatory shear flows

TL;DR

This study investigates how dense suspensions of elliptical particles respond rheologically under oscillatory shear, revealing unique orientational arrest phenomena and the influence of friction and strain amplitude on particle orientation and jamming.

Contribution

It uncovers the orientational arrest of elliptical particles at low strains and shows how friction and strain amplitude affect the system's ability to escape these states.

Findings

Frictionless ellipses get dynamically arrested in their initial orientation at small strains.

Oscillatory shear respects Cox-Merz rule at large strains but not at low strains.

Larger strains or friction enable the system to escape orientational arrest and reach disordered states.

Abstract

We study the rheological response of dense suspensions of elliptical particles, with an aspect ratio equal to 3, under oscillatory shear flows and imposed pressure by numerical simulations. Like for the isotropic particles, we find that the oscillatory shear flows respect the Cox-Merz rule at large oscillatory strains but differ at low strains, with a lower viscosity than the steady shear and higher shear jamming packing fractions. However, unlike the isotropic cases (i.e., discs and spheres), frictionless ellipses get dynamically arrested in their initial orientational configuration at small oscillatory strains. We illustrate this by starting at two different configurations with different nematic order parameters and the average orientation of the particles. Surprisingly, the overall orientation in the frictionless case is uncoupled to the rheological response close to jamming, and the rheology is only controlled by the average number of contacts and the oscillatory strain. Having larger oscillatory strains or adding friction does, however, help the system escape these orientational arrested states, which are evolving to a disordered state independent of the initial configuration at low strains and ordered ones at large strains.