Discontinuous Shear Thickening in Brownian Suspensions By Dynamic Simulation

TL;DR

This study uses dynamic simulations to reveal that discontinuous shear thickening in Brownian suspensions is primarily a geometric transition influenced by contact forces, aligning well with experimental data.

Contribution

It demonstrates that shear thickening in colloidal suspensions is a geometric phenomenon driven by contact forces, extending understanding beyond hydrodynamic effects.

Findings

Shear thickening is a stress-induced transition to frictional contact networks.

Brownian and repulsive forces' effects on onset stress are additive.

Simulation results match experimental viscosity and normal stress differences.

Abstract

Dynamic particle-scale numerical simulations are used to show that the shear thickening observed in dense colloidal, or Brownian, suspensions is of a similar nature to that observed in non-colloidal suspensions, i.e., a stress-induced transition from a flow of lubricated near-contacting particles to a flow of a frictionally contacting network of particles. Abrupt (or discontinuous) shear thickening is found to be a geometric rather than hydrodynamic phenomenon; it stems from the strong sensitivity of the jamming volume fraction to the nature of contact forces between suspended particles. The thickening obtained in a colloidal suspension of purely hard frictional spheres is qualitatively similar to experimental observations. However, the agreement cannot be made quantitative with only hydrodynamics, frictional contacts and Brownian forces. Therefore the role of a short-range repulsive potential mimicking the stabilization of actual suspensions on the thickening is studied. The effects of Brownian and repulsive forces on the onset stress can be combined in an additive manner. The simulations including Brownian and stabilizing forces show excellent agreement with experimental data for the viscosity $\eta$ and the second normal stress difference $N_2$.