Influence of shear stress applied during flow stoppage and rest period on the mechanical properties of thixotropic suspensions

TL;DR

This study reveals that shear stress during flow stoppage significantly influences the mechanical properties of thixotropic suspensions, highlighting the importance of stress history in their solidification process.

Contribution

It demonstrates that shear stress during the liquid-solid transition critically affects the elastic modulus and yield stress of thixotropic suspensions, a novel insight into their mechanical behavior.

Findings

Elastic modulus and yield stress depend strongly on shear stress during flow stoppage.

Mechanical properties are minimally affected by preshear or resting shear stress.

Suspensions age with a structuration rate largely independent of stress history.

Abstract

We study the solid mechanical properties of several thixotropic suspensions as a function of the shear stress history applied during their flow stoppage and their aging in their solid state. We show that their elastic modulus and yield stress depend strongly on the shear stress applied during their solid-liquid transition (i.e., during flow stoppage) while applying the same stress only before or only after this transition may induce only second-order effects: there is negligible dependence of the mechanical properties on the preshear history and on the shear stress applied at rest. We also found that the suspensions age with a structuration rate that hardly depends on the stress history. We propose a physical sketch based on the freezing of a microstructure whose anisotropy depends on the stress applied during the liquid-solid transition to explain why the mechanical properties depend strongly on this stress. This sketch points out the role of the internal forces in the colloidal suspensions' behavior. We finally discuss briefly the macroscopic consequences of this phenomenon and show the importance of using a controlled-stress rheometer.