Bulk and interfacial rheology of emulsions stabilized with clay particles

Abstract

This contribution aims to investigate the stabilizing effect of clay particles on oil-in-water emulsions using bulk and interfacial rheological measurements. Depending on the surface properties of clay particles, the emulsion showed different rheological responses as a result of different stabilization behavior. Hydrophilic clays (natural montmorillonite (NMt)) stabilized the emulsion via an interfacial layer with distinguished interfacial modulus (G*interface), while hydrophobic clays (organically modified montmorillonite (OMt)) stabilized the emulsion by increasing the bulk modulus of the oil phase (G*oil). In composite systems, when NMt is present together with cationic surfactant or OMt, complex formation at the oil-water interface significantly influenced the rheological response and emulsion stability. The high interfacial modulus (G*interface) of the composite interface stabilized the flocculated droplets more than the repulsive interaction between droplets. As a consequence, the bulk modulus of the emulsion (G*emulsion) also increases. Finally it could be shown that with increasing interfacial area (oil-to-water ratio), microscopic and macroscopic stabilization of emulsions could be improved. Rheological study provided structural information of the complex interface and defined the role of clay particles for the stabilization.