Jamming Distance Dictates Colloidal Shear Thickening

TL;DR

This study investigates how jamming distance influences shear thickening in colloidal suspensions, revealing that surface roughness affects contact number requirements and free volume, with implications for understanding suspension rheology.

Contribution

It introduces the concept that jamming distance governs shear thickening and shows how surface roughness alters contact mechanics and free volume near jamming.

Findings

Shear thickening strength scales exponentially with scaled jamming distance.

Rough colloids require fewer contacts to achieve the same shear thickening.

Surface roughness affects free volume and contact force distribution.

Abstract

We report experimental and computational observations of dynamic contact networks for colloidal suspensions undergoing shear thickening. The dense suspensions are comprised of sterically stabilized poly(methyl methacrylate) hard sphere colloids that are spherically symmetric and have varied surface roughness. Confocal rheometry and dissipative particle dynamics simulations show that the shear thickening strength scales exponentially with the scaled deficit contact number and the scaled jamming distance. Rough colloids, which experience additional tangential and rolling constraints, require an average of 1.5 - 2 fewer particle contacts as compared to smooth colloids, in order to generate the same shear thickening strength. This is because the surface roughness enhances geometric friction in a way that the rough colloids do not experience a large change in the free volume near the jamming point. In contrast, smooth colloids must undergo significant reduction in the free volume to support an equivalent shear stress. The available free volume for different colloid roughness is related to the deficiency from the maximum number of nearest neighbors at jamming under shear. Our results further suggest that the force per contact is different for particles with different morphologies.