On the addition of micron-size intruders in a shear-thickening suspension of nanoparticles

TL;DR

This paper explores how adding large intruders affects the shear-thickening behavior of nanoparticle suspensions, revealing that size ratio critically influences whether thickening is enhanced or suppressed.

Contribution

It demonstrates that large intruders can shift the onset and reduce the strength of shear-thickening in nanoparticle suspensions, highlighting the importance of particle size ratio.

Findings

Granules lower the shear rate at which thickening begins.

Thickening transitions from discontinuous to continuous with granule addition.

Large size ratio disrupts force chain formation, altering rheology.

Abstract

This study investigates the rheological behavior of shear-thickening suspensions made of different types of nanoparticles upon the addition of large intruders referred to as granules. The size ratio ranges from 20 to 120. We examine the effects of granule size, volume fraction, and surface properties on shear-thickening characteristics. Starting with a fumed silica suspension exhibiting discontinuous shear thickening (DST) without granules, the addition of granules at different volume fractions, shifts the onset of thickening to lower shear rates. Concomitantly, the strength of the thickening, quantified by the thickening index, decreases, transitioning from DST to continuous shear thickening (CST). Comparison with suspensions of nanosilica spheres reveals a similar trend, suggesting generality across different systems. However, these results contrast with cornstarch-based suspensions, where granule addition enhances thickening. This difference is attributed to the large size ratio studied here: When the granules are much larger than the particles in the interstitial suspension, the granules introduce a spread in the local shear rate and disrupt the particles' ability to form an extended fabric of force chains. The findings highlight the critical role of particle size ratio in determining the rheology of complex suspensions, paving the way for tailoring material properties in industrial and scientific applications.