Viscosity of Concentrated Water-in-Oil Emulsions within the Framework of the Structural Model

A structural rheological model is used to interpret the viscosity curves and flow curves of concentrated emulsions consisting of water droplets in oil. It is shown that the rheological curves can be divided into separate intervals of shear rates, within which the experimental data are approximated by the rheological equations of the structural model. The generalized flow equation describes the breakdown of the emulsion structure under the action of tensile hydrodynamic forces. The second rheological equation additionally includes a rate constant related to the process of droplet aggregate formation under the action of compressive hydrodynamic forces. The dependence of the generalized flow equation coefficients ₂^{1/2} and ₂^{1/2} on the volume fraction Φ is described by separate equations which utilize hydrodynamic parameters. The compactness coefficient χ, associated with the spontaneous rupture of droplets, changes in a complex manner with increasing concentration, which may be related to the formation of aggregates and the change in droplet shape due to deformation upon droplet contact.