Discontinuous Shear Thickening in Cornstarch Suspensions

We study the emergence of discontinuous shear-thickening (DST) in cornstarch, the well know system for this phenomenon, by combining macroscopic rheometry with local Magnetic Resonance Imaging (MRI) measurements. We bring evidence that macroscopic DST is characterized in wide gap with a shear localization, part of the material close to the inner cylinder is flowing and the rest is not. The flow seperates into a low-density flowing and a high-density jammed region. Moreover, the local rheology of the flowing region does not directly reflect DST but, strikingly, is most often shear-thinning. Our data are not consistent with recent theoretical suggestions based on the presumed existence of s-shaped flow curves. Instead, they support that DST should be attributed to the existence of a shear jamming limit at volume fractions quite significantly below random close packing.