Yielding and fracturing of concentrated emulsions in narrow gaps

Abstract

We used rheology and confocal microscopy techniques to characterise the flow of emulsions as the droplets were confined by increasing the drop volume fraction and reducing the distance between the shearing surfaces. Slip was minimised by matching the density of the oil and water phases. Attractive interactions between the drops caused them to flocculate. The contribution of the emulsion microstructure to its shear response becomes significant when the oil drop flocs almost span the distance between the surfaces. We found that confining the flow of droplet flocs causes a transition from a fluid phase with shear thinning flow behaviour into a jammed, solid-like material. The large deformations caused by flow at the maximum drop packing fraction induce droplet coalescence within highly localised regions of the emulsion.