Non-monotonic flow curves of shear thickening suspensions

TL;DR

This paper investigates the non-monotonic flow behavior in shear thickening suspensions, revealing complex flow curves and stability conditions through novel stress-controlled simulations, advancing understanding of DST phenomena.

Contribution

It introduces the concept of non-monotonic steady-state flow curves in shear thickening suspensions and explores their stability and physical implications.

Findings

Identification of non-monotonic flow curves analogous to equations of state

Observation of flow only at small stresses above shear jamming

Uniform shear flow remains stable during thickening transition

Abstract

The discontinuous shear thickening (DST) of dense suspensions is a remarkable phenomenon in which the viscosity can increase by several orders of magnitude at a critical shear rate. It has the appearance of a first order phase transition between two hypothetical "states" that we have recently identified as Stokes flows with lubricated or frictional contacts, respectively. Here we extend the analogy further by means of novel stress-controlled simulations and show the existence of a non-monotonic steady-state flow curve analogous to a non-monotonic equation of state. While we associate DST with an S-shaped flow curve, at volume fractions above the shear jamming transition the frictional state loses flowability and the flow curve reduces to an arch, permitting the system to flow only at small stresses. Whereas a thermodynamic transition leads to phase separation in the coexistence region, we observe a uniform shear flow all along the thickening transition. A stability analysis suggests that uniform shear may be mechanically stable for the small Reynolds numbers and system sizes in a rheometer.