How does a concentrated emulsion flow?: Yielding, local rheology, and wall slip

Using high-frequency ultrasonic velocimetry, we perform simultaneously rheological and local velocity measurements in a 75% wt. concentrated emulsion after a step-like shear rate applied for 3 h. Velocity profiles in the vicinity of the yield stress unveil the existence of transient inhomogeneous flows. However, approaching the equilibrium, banded states disappear and the emulsion flows homogeneously. At higher shear rates, we show that the local rheological behaviour evolves with the imposed shear rate. Changes in droplet concentration may be responsible for such a behaviour. We finally point out the presence of wall slip and investigate the evolution of the lubricating layers’ thicknesses with the shear stress.