Generality of shear thickening in suspensions

TL;DR

This paper demonstrates that shear thickening in suspensions is more common than previously thought and can be masked by yield stress, which can be controlled to reveal shear thickening behavior, enabling new smart fluid designs.

Contribution

It shows that shear thickening is a general phenomenon masked by yield stress and provides a method to recover it across various suspension systems.

Findings

Shear thickening can be masked by yield stress.

Reducing yield stress reveals shear thickening behavior.

Control of yield stress enables design of smart suspensions.

Abstract

Suspensions are of wide interest and form the basis for many smart fluids. For most suspensions, the viscosity decreases with increasing shear rate, i.e. they shear thin. Few are reported to do the opposite, i.e. shear thicken, despite the longstanding expectation that shear thickening is a generic type of suspension behavior. Here we resolve this apparent contradiction. We demonstrate that shear thickening can be masked by a yield stress and can be recovered when the yield stress is decreased below a threshold. We show the generality of this argument and quantify the threshold in rheology experiments where we control yield stresses arising from a variety of sources, such as attractions from particle surface interactions, induced dipoles from applied electric and magnetic fields, as well as confinement of hard particles at high packing fractions. These findings open up possibilities for the design of smart suspensions that combine shear thickening with electro- or magnetorheological response.