Three-dimensional jamming and flows of soft glassy materials

TL;DR

This paper demonstrates that soft glassy materials can be described by a simple 3D continuum model, revealing their unjammed behavior in secondary flows and shear-dependent viscosity, advancing understanding of their nonlinear rheology.

Contribution

It introduces a novel 3D continuum framework for soft glassy materials, linking their unjammed secondary flows and shear relaxation to a plasticity-based jamming criterion.

Findings

No yield resistance to secondary flows in any direction.

Materials behave as simple liquids orthogonal to main flow.

Viscosity inversely proportional to shear rate, indicating shear-induced relaxation.

Abstract

Various disordered dense systems such as foams, gels, emulsions and colloidal suspensions, exhibit a jamming transition from a liquid state (they flow) to a solid state below a yield stress. Their structure, thoroughly studied with powerful means of 3D characterization, exhibits some analogy with that of glasses which led to call them soft glassy materials. However, despite its importance for geophysical and industrial applications, their rheological behavior, and its microscopic origin, is still poorly known, in particular because of its nonlinear nature. Here we show from two original experiments that a simple 3D continuum description of the behaviour of soft glassy materials can be built. We first show that when a flow is imposed in some direction there is no yield resistance to a secondary flow: these systems are always unjammed simultaneously in all directions of space. The 3D jamming criterion appears to be the plasticity criterion encountered in most solids. We also find that they behave as simple liquids in the direction orthogonal to that of the main flow; their viscosity is inversely proportional to the main flow shear rate, as a signature of shear-induced structural relaxation, in close similarity with the structural relaxations driven by temperature and density in other glassy systems.