Effect of droplet size on the rheology of emulsions

TLDR

The study investigates how droplet size affects the rheological behavior of water‑in‑oil and oil‑in‑water emulsions. The authors used a controlled‑stress rheometer to measure viscosity, storage and loss moduli across varying droplet sizes. Droplet size dramatically influences rheology: fine emulsions show higher viscosities, storage moduli, and stronger shear‑thinning; mixing fine and coarse droplets produces a rheological minimum at a specific fine‑droplet proportion only at low shear stresses, while at high stresses viscosity increases with more fine droplets; water‑in‑oil emulsions age faster than oil‑in‑water emulsions.

Abstract

Abstract The effect of droplet size on the rheological behavior of water‐in‐oil and oil‐in‐water emulsions was investigated using a controlled‐stress rheometer. Results indicate that the droplet size has a dramatic influence on emulsion rheology. Fine emulsions (water‐in‐oil or oil‐in‐water) have much higher viscosities and storage moduli than the corresponding coarse emulsions. The shear‐thinning effect is much stronger in the case of fine emulsions. When coarse droplets are replaced by fine droplets (keeping total volume fraction of the dispersed phase constant), the resulting emulsion exhibits a minimum in rheological properties (viscosity, storage and loss moduli, time constant) at a certain proportion of fine droplets. However, the minimum in viscosity occurs only at low shear stresses. At high stresses, the viscosity of the mixed emulsion increases as the proportion of fine droplets increases. The study of the aging effect on the rheological behavior shows that water‐in‐oil emulsions age much more rapidly than the oil‐in‐water emulsions.