Shear Thickening and Scaling of the Elastic Modulus in a Fractal Colloidal System with Attractive Interactions

TL;DR

This study investigates how fractal colloidal dispersions with attractive interactions exhibit shear thickening and shear thinning, revealing the role of cluster breakup and residual stress in gel elasticity.

Contribution

It introduces a scaling model linking shear-induced cluster breakup to the elastic modulus and residual stress in fractal colloidal gels.

Findings

Shear thickening occurs at shear rates around 10^2-10^3 s^-1.

Post-shear, gels show increased elastic modulus proportional to residual stress.

A simple scaling model explains the shear breakup of fractal clusters.

Abstract

Dilute oil dispersions of fractal carbon black particles with attractive Van der Waals interactions display continuous shear thickening followed by shear thinning at high shear rates. The shear thickening transition occurs at $\dot\gamma_{c}\approx 10^{2}-10^{3}s^{-1}$ and is driven by hydrodynamic breakup of clusters. Pre-shearing dispersions at shear rates $\dot\gamma>\dot\gamma_{c}$ produces enhanced-modulus gels where $G' \sim \sigma_{pre-shear}^{1.5-2}$ and is directly proportional to the residual stress in the gel measured at a fixed sample age. The observed data can be accounted for using a simple scaling model for the breakup of fractal clusters under shear stress.