Unifying shear thinning behaviors of meso-scaled particle suspensions

TL;DR

This paper reveals that flow-induced particle aggregation due to inter-particle interactions causes non-Newtonian behavior in meso-scaled suspensions, and introduces a dimensionless number to unify their rheological properties across different conditions.

Contribution

It introduces a dimensionless number that unifies the rheology of meso-scaled suspensions by accounting for hydrodynamic and inter-particle interactions, bridging micro- and macro-scale systems.

Findings

Flow-induced particle aggregation explains non-Newtonian behavior.

A dimensionless number unifies rheological behavior across conditions.

The model predicts suspension rheology based on particle interactions.

Abstract

The rheology of suspensions with meso-scaled particles [with size of $O(10^2)\ \text{nm}$ to $O(10)\ \mu\text{m}$] is intriguing since significant non-Newtonian behaviors are widely observed although the thermal fluctuation (Brownain motion) of the meso-scaled particles is negligible. Here, we show that the linear constitutive relation for such systems fails due to a flow-induced particle aggregation, which originates from the inherent inter-particle interactions, e.g., the weakly adhesive van der Waals interaction. This accounts for the temporal evolution of the rheological property in both steady and oscillatory shear flows. A dimensionless number that measures the importance of the hydrodynamic interaction in shear flow with respect to the inter-particle interaction, {is} proposed, through which the non-linear constitutive relation for suspensions with various particle sizes, particle concentrations, as well as flow conditions could be unified. This investigation bridge \mdf{the gap between micro- and macro-scaled suspension systems} and make the rheology of the meso-scaled suspensions predictable.