Shear Thickening of Cornstarch Suspensions as a Reentrant Jamming Transition

Abstract

We study the rheology of cornstarch suspensions, a non-Brownian particle system that exhibits shear thickening. From magnetic resonance imaging velocimetry and classical rheology it follows that as a function of the applied stress the suspension is first solid (yield stress), then liquid, and then solid again when it shear thickens. For the onset of thickening we find that the smaller the gap of the shear cell, the lower the shear rate at which thickening occurs. Shear thickening can then be interpreted as the consequence of dilatancy: the system under flow wants to dilate but instead undergoes a jamming transition because it is confined, as confirmed by measurement of the dilation of the suspension as a function of the shear rate.

Does Shear Thickening Occur in Semisolid Metals?

“…This is the phenomenon observed with dense suspensions of cornstarch in water, which allows someone to run across the surface of the suspension in a swimming bath for example (but when they stand still they sink in). Brown et al [6] have argued that all suspensions should show shear thickening under certain conditions because the underlying mechanisms (hydrodynamics, [7,8] dilatation [9][10][11] ) are general but they demonstrate that shear thickening can be masked by a yield stress. They attribute discontinuous shear thickening to frictional particle contacts that form when dense particle arrangements begin to dilate and push against boundaries.…”

Discontinuous Shear Thickening in Cornstarch Suspensions

“…Examples abound, however, in granular suspension rheology where the macroscopic response is sharply different from the local behaviour: the apparent yield stress [13,14] or a transient DST behavior [10], for example, were both shown to result from the emergence of flow inhomogeneities due respectively to density differences and migration. The observation of finite size effects in DST measurements [2,11], at sizes up to 100 particles, questions the idea that DST is a purely local phenomenon. In this context, it is unclear how a phase diagram for the local response can be deduced from experimental data and compared with numerical [5], and theoretical [6] works.…”

“…Proposed mechanisms include: the crossover to Bagnold scaling due to particle inertia [10]; the coupling between normal and shear stresses associated with material dilatancy [11,12]. In numerical simulations DST was observed in systems which are forced to remain homogeneous by periodic boundary conditions [5].…”

Volume fraction variations and dilation in colloids and granulars

“…The experiments in Cates et al (2005), Fall et al (2008) and Haw (2004), as well as a large body of rheological literature (e.g. Metzner & Whitlock 1958), demonstrate that concentrated suspensions are 'naturally' prone to respond by dilation.…”

“…fluid interfaces (Cates et al 2005), the total volume must be conserved. Recent experiments demonstrate that rheological jamming in cornstarch suspensions (not strictly colloidal) is directly associated with global dilation (Fall et al 2008). Consideration of local variations in volume fraction illustrates that dilation can happen in colloidal suspensions, albeit local dilation rather than global, even in a confined geometry such as a channel flow (Haw 2004).…”