Fiber optic Doppler anemometry (FODA) as a tool in formulating emulsions

Abstract

Fiber optic Doppler anemometry (FODA) was used to determine the mean droplet radius and the relative number of droplets in a model olive oil emulsion. The model emulsion consisted of 40% olive oil in water with a nonionic surfactant mixture. Surfactant ratio, total surfactant concentration, and the initial distribution of the two surfactants were studied. The optimal surfactant ratio to produce the smallest mean droplet radius and the greatest relative number of droplets corresponded to an HLB of 9. The optimum total surfactant concentration was directly related to the olive oil concentration in the formulation. Also, the optimum insonation time and processing volume were determined. Droplet interactions were detected in the optimized emulsion formulation. The emulsion had a zeta potential of −36.7 mV. Replacement of a small portion of the nonionic surfactants with sodium lauryl sulfate while maintaining the overall HLB resulted in a zeta potential of −55.6 mV. Analysis by FODA indicated that the more negative surface charge increased the repulsive droplet interactions. In contrast, replacement of the nonionic surfactants with dodecyltrimethylammonium bromide resulted in a zeta potential of −17.1 mV, and enhanced attractive droplet interactions were detected by FODA.