Role of viscoelastic interfaces in emulsion rheology and drop deformation

Abstract

The small-deformation behavior of single Newtonian oil drops covered by an adsorbed viscoelastic protein layer and suspended in a Newtonian protein-free matrix phase was investigated in simple shear flow. A simple but effective technique is presented to coat the drops with a layer of surface-active protein (lysozyme), which was adsorbed irreversibly to the oil/water interface. The adsorption and network formation at the interface are tracked by interfacial shear and dilatational rheometry using a biconical disk interfacial rheometer and pendant drop tensiometry. While the clean drop is deforming to the expected ellipsoidal shape in shear flow according to the Taylor theory, the protein-covered drop is able to resist the bulk shear stress to a much higher degree. We propose that this effect is due to the adsorbed protein, which is known to form strong, gel-like viscoelastic networks when adsorbed at oil/water interfaces.

Keywords

interfacial gels / globular proteins / interfacial rheology / drop deformation / emulsions