Single-Parameter and Two-Parameter Rheological Equations of State for Nondilute Emulsions

The existing viscosity−concentration equations for concentrated emulsions of nearly spherical noncolloidal droplets are first reviewed. The equations of emulsion relative viscosity η r vs volume fraction of dispersed-phase φ existing in the literature are characterized as single-parameter equations because viscosity ratio (ratio of dispersed-phase viscosity to continuous-phase viscosity) is the only parameter in the equations. The equations are evaluated in light of a large body of experimental data for concentrated emulsions, covering a broad range of viscosity ratios. The existing equations generally give good predictions of relative viscosity only at low values of φ (φ < 0.2). Several new equations are proposed and evaluated with experimental data. The proposed η r vs φ equations are characterized as two-parameter equations because they contain two parameters, namely, the viscosity ratio and φ m, the maximum packing volume fraction of droplets. The proposed equations generally show good agreement with the experimental data.