Constraint ratio controls viscosity in shear thickening suspensions

TL;DR

This paper presents a constraint-counting model that explains how microscopic contact mechanics influence the viscosity increase in shear thickening suspensions, enabling universal data collapse and predictive insights.

Contribution

The introduced model incorporates friction and dimensionality to unify rheological data and identify the constraint ratio as the key control parameter for shear thickening.

Findings

Data collapse onto a universal master curve.

Constraint ratio effectively predicts viscosity changes.

Model unifies microscopic contact mechanics with macroscopic flow behavior.

Abstract

The dramatic viscosity increase observed in dense suspensions under shear poses a major challenge in our understanding of how microscopic contact mechanics translate into macroscopic flow resistance. Here, we introduce a constraint-counting model that incorporates friction and dimensionality naturally without additional assumptions and allows for collapsing of rheological data onto a universal master curve. In this model, we borrow ideas from dry granular jamming physics and classify contacts as either locked or non-locked to define a single state variable, the constraint ratio, which measures the average strength of mechanical constraint per particle. By identifying the constraint ratio as the key control parameter, our framework provides a unifying route toward predictive modeling and rational design of shear-thickening materials.