Yield stress aging in attractive colloidal suspensions

TL;DR

This study reveals that yield stress aging in attractive colloidal suspensions is governed by a time-dependent rolling threshold at the particle contact scale, linking microscopic contact mechanics to macroscopic rheological properties.

Contribution

It introduces a novel contact-scale model for yield stress aging, connecting microscopic contact mechanics with macroscopic suspension behavior.

Findings

Rolling threshold grows logarithmically with time.

Contact-scale flexural rigidity determines yield stress aging.

Macroscopic shear modulus relates to yield stress through a universal relation.

Abstract

We investigate the origin of yield stress aging in semi-dense, saline, and turbid suspensions in which structural evolution is rapidly arrested by the formation of thermally irreversible roll-resisting interparticle contacts. By performing optical tweezer (OT) three-point bending tests on particle rods, we show that these contacts yield by overcoming a rolling threshold, the critical bending moment of which grows logarithmically with time. We demonstrate that this time-dependent contact-scale rolling threshold controls the suspension yield stress and its aging kinetics. We identify a simple constitutive relation between the contact-scale flexural rigidity and rolling threshold, which transfers to macroscopic scales. This leads us to establishing a constitutive relation between macroscopic shear modulus and yield stress that is generic for an array of colloidal systems.