Disentangling microstructural elements of shear thickening suspensions via computer simulations of a minimal model

TL;DR

This study uses 2D simulations of a minimal model to analyze microstructural changes in shear thickening suspensions, revealing distinct contact network structures and force distributions associated with thickening and thinning.

Contribution

It identifies specific microstructural building blocks and force distributions that characterize shear thickening, providing new insights into suspension rheology.

Findings

Contact networks show sharp peaks in radial distribution functions during steady flow.

Non-Gaussian stress fluctuations with power law tails emerge during thickening.

Percolation of strong contact force networks correlates with shear thickening.

Abstract

We use a minimal model for a dense suspension undergoing thickening and thinning to investigate microstructural changes in 2d simulations. Our simulations show that in steady flow the contact network contains distinct building blocks which are clearly signaled by sharp peaks in the radial distribution function, similar to what is observed in granular jamming. These structures {deform} during thinning. Non-Gaussian stress fluctuations that only emerge during thickening are associated to power law tails in the distribution of local contact forces, which tend to emerge when the flow-induced building blocks form large spanning assemblies. The subset of the contact network characterized by strong contact forces and connectivity large enough to be rigid or over-constrained is increasingly likely to percolate as the system starts to thicken, and to percolate over larger strain windows during thickening. The tendency of these structures to span the sample and to persist is dramatically reduced during thinning, where instead their deformation allows for a more homogeneous spatial redistribution of contact forces, significantly reducing the fluctuations of the macroscopic stress over time.