Rheology of high internal phase ratio emulsions

The rheology of high internal phase ratio oil-in-water emulsions was investigated experimentally using a controlled-stress rheometer. Steady shear, oscillatory shear, and creep/recovery measurements were carried out on a series of highly concentrated fine (Sauter mean radius 1.28 μm), coarse (Sauter mean radius 1.95 μm), and mixed fine-and-coarse emulsions. The dispersed-phase (oil) concentration ranged from 78.55% to 94.02% by volume. All the emulsions investigated in this study possessed a yield stress. The yield stress values obtained from different experiments for the same emulsion showed good agreement with each other. Both yield stress and storage modulus of the emulsions increased with the increase in the dispersed-phase concentration and with the decrease in the average droplet size. When coarse droplets were replaced by fine droplets (keeping total volume fraction of the dispersed-phase constant), the resulting emulsion exhibited an increase in the yield stress and storage modulus due to a decrease in the average droplet size. The Princen and Kiss equations were used to interpret the yield stress and storage modulus data of this study.