Federico Toschi (Eindhoven) - Unified theoretical and experimental view on transient shear banding

Dense emulsions, colloidal gels, microgels, and foams all display a solid-like behaviour at rest characterised by a yield stress, above which the material flows like a liquid. Such a fluidisation transition often consists of long-lasting transient flows that involve shear-banded velocity profiles. The characteristic time for full fluidisation has been reported to decay as a power-law of the shear rate and of the shear stress with two distinct respective exponents. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the Herschel-Bulkley law that describes the steady-state flow behaviour of these complex fluids. Here we introduce a continuum model based on the minimisation of an out-of-equilibrium free energy that captures quantitatively all the salient features associated with such transient shear-banding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steady-state flow properties of yield stress fluids.

Reference: arxiv.org/abs/1907.08846