Tuning the shear-thickening of suspensions through surface roughness and physico-chemical interactions

TL;DR

This study investigates how surface roughness and chemical interactions influence shear thickening in suspensions, revealing the roles of hydrogen bonds and friction, and demonstrating tunable shear-thickening behavior through particle surface modifications.

Contribution

It provides experimental evidence that both surface roughness and chemistry affect shear thickening, especially highlighting the importance of hydrogen bonds for discontinuous shear thickening.

Findings

Hydrogen bonds are crucial for discontinuous shear thickening.

Surface roughness influences the onset of shear thickening.

Mixtures of particles with different surface chemistries allow tuning of shear response.

Abstract

Shear thickening denotes the reversible increase in viscosity of a suspension of rigid particles under external shear. This ubiquitous phenomenon has been documented in a broad variety of multiphase particulate systems, while its microscopic origin has been successively attributed to hydrodynamic interactions and frictional contact between particles. The relative contribution of these two phenomena to the magnitude of shear thickening is still highly debated and we report here a discriminating experimental study using a model shear-thickening suspension that allows us to tune independently both the surface chemistry and the surface roughness of the particles. We show here that both properties matter when it comes to continuous shear thickening (CST) and that the presence of hydrogen bonds between the particles is essential to achieve discontinuous shear thickening (DST) by enhancing solid friction between closely contacting particles. Moreover, a simple argument allows us to predict the onset of CST, which for these very rough particles occurs at a critical volume fraction much lower than that previously reported in the literature. Finally, we demonstrate how mixtures of particles with opposing surface chemistry make it possible to finely tune the shear-thickening response of the suspension at a fixed volume fraction, paving the way for a fine control of the shear-thickening transition in engineering applications.