Disentangling glass and jamming physics in the rheology of soft materials

TL;DR

This study demonstrates that the shear rheology of soft materials can be modeled as a linear combination of glass and jamming physics, with experimental and numerical data supporting the additive approach across various systems.

Contribution

It introduces a simple additive model for shear stress in soft materials, unifying glass and jamming physics contributions and validating it with extensive experimental and simulation data.

Findings

Flow curves are well described by the additive model.

Colloidal hard spheres are governed by glass physics.

Aqueous foams are dominated by jamming effects.

Abstract

The shear rheology of soft particles systems becomes complex at large density because crowding effects may induce a glass transition for Brownian particles, or a jamming transition for non-Brownian systems. Here we successfully explore the hypothesis that the shear stress contributions from glass and jamming physics are `additive'. We show that the experimental flow curves measured in a large variety of soft materials (colloidal hard spheres, microgel suspensions, emulsions, aqueous foams) as well as numerical flow curves obtained for soft repulsive particles in both thermal and athermal limits are well described by a simple model assuming that glass and jamming rheologies contribute linearly to the shear stress, provided that the relevant scales for time and stress are correctly identified in both sectors. Our analysis confirms that the dynamics of colloidal hard spheres is uniquely controlled by glass physics while aqueous foams are only sensitive to jamming effects. We show that for micron-sized emulsions both contributions are needed to successfully account for the flow curves, which reveal distinct signatures of both phenomena. Finally, for two systems of soft microgel particles we show that the flow curves are representative of the glass transition of colloidal systems, and deduce that microgel particles are not well suited to studying the jamming transition experimentally.