Nonlocal effects in the shear banding of a thixotropic yield stress fluid

We observe a novel type of shear banding in the rheology of thixotropic yield-stress fluids that is due to the coupling of both nonlocality and thixotropy. The latter is known to lead to shear banding even in homogeneous stress fields. Yet, in the presence of nonlocal effects such bands appear smoothed by the continuous shear rate variation across the shear band. Here, we introduce a simple nonlocal model for the shear banding (NL-SB), and we implement it for the analysis of sub-mm rheo-MRI velocimetry measurements of a milk microgel suspension in a cone-and-plate geometry. The proposed NL-SB model enables quantifying the cooperativity length, yielding values in the order of the aggregate size in the microgel.