Yielding and flow of concentrated Pickering emulsions

Abstract

We have used rheo-imaging to investigate the shear flow of particle-stabilized (Pickering) emulsions with different interactions between droplets. To minimize creaming, we have worked with arrested networks of droplets. We observe three different yielding mechanisms as well as shear thickening at high strain. Pickering emulsions comprised of repulsive droplets respond to small strains initially by reversible movement, then, as the strain is increased, yielding occurs via cage breaking. At large strains there is a peak in both moduli and correlations between droplet trajectories indicative of shear thickening and jamming. Pickering emulsions comprised of attractive droplets share similar features and additionally have a loss modulus peak at low strain associated with the breakage and rearrangement of the attractive bonds. We observe that small attractive droplets already start to move irreversibly at small strains even though yielding has not yet occurred. As the strain is increased, the percolating network of larger droplets is eventually completely broken and the sample yields as a whole. Finally, we explore what happens when a highly compressed emulsion or bi-liquid foam is subjected to shear flow: we find that at high strain the particles fail to stabilize the interface and the emulsion is destroyed.