Emulsion Stability in the Presence of Nonionic Surfactant Micelles: Role of Micellar Ordering and Ostwald Ripening

Abstract

The phenomenon of surfactant micelle ordering (i.e., stratification) in emulsion films was investigated using the reflected-light microinterferometric technique. In thinning films formed from a nonionic micellar solution of ethoxylated alcohol (1 wt %), it was found that the small droplets (i.e., less than 5 µm) are separated by thick (>0.1 µm) stable films containing surfactant micelles in multilayers that prevent droplet flocculation and coalescence. The Ostwald ripening process governs emulsion stability over a long-term. The direct microscopic observations of the evolution of the drop size distribution over time of hexadecane drops (∼25 vol %) dispersed in an aqueous micellar solution (≈ 120 times critical micellar concentration) was compared with that calculated from the Ostwald ripening model