Dynamics of Localized Stresses in Shear-thickening Cornstarch Suspensions

Dense colloidal and cornstarch suspensions are common examples of shear thickening suspensions. Spatially resolved surface stresses in a model colloidal suspension using boundary stress microscopy (BSM) revealed dynamic regions of substantially increased local stresses that appear intermittently and move in shear direction. We report BSM of cornstarch suspensions and also find large stress heterogeneities, but with very different dynamics. Above critical stress, the heterogeneous regions propagate along the vorticity direction, perpendicular to shear direction, while only at higher applied stresses we do observe propagation in the shear direction similar to the behavior observed in colloidal suspensions.