Competing Timescales Lead to Oscillations in Shear-Thickening Suspensions.

Competing timescales generate novelty. Here, we show that a coupling between the timescales imposed by instrument inertia and the formation of interparticle frictional contacts in shear-thickening suspensions leads to highly asymmetric shear-rate oscillations. Experiments tuning the presence of oscillations by varying the two timescales support our model. The observed oscillations give access to a shear-jamming portion of the flow curve that is forbidden in conventional rheometry. Moreover, the oscillation frequency allows us to quantify an intrinsic relaxation time for particle contacts. The coupling of fast contact network dynamics to a slower system variable should be generic to many other areas of dense suspension flow, with instrument inertia providing a paradigmatic example.

Constraint-Based Approach to Granular Dispersion Rheology.

We present a phenomenological model for granular suspension rheology in which particle interactions enter as constraints to relative particle motion. By considering constraints that are formed and released by stress respectively, we derive a range of experimental flow curves in a single treatment and predict singularities in viscosity and yield stress consistent with literature data. Fundamentally, we offer a generic description of suspension flow that is independent of bespoke microphysics.

Erratum: Towards a Unified Description of the Rheology of Hard-Particle Suspensions [Phys. Rev. Lett. 115, 088304 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.115.088304.

Towards a Unified Description of the Rheology of Hard-Particle Suspensions.

The rheology of suspensions of Brownian, or colloidal, particles (diameter d≲1 µm) differs markedly from that of larger grains (d≳50 µm). Each of these two regimes has been separately studied, but the flow of suspensions with intermediate particle sizes (1 µm≲d≲50 µm), which occur ubiquitously in applications, remains poorly understood. By measuring the rheology of suspensions of hard spheres with a wide range of sizes, we show experimentally that shear thickening drives the transition from colloidal to granular flow across the intermediate size regime. This insight makes possible a unified description of the (noninertial) rheology of hard spheres over the full size spectrum. Moreover, we are able to test a new theory of friction-induced shear thickening, showing that our data can be well fitted using expressions derived from it.