CHARACTERIZATION OF MINIEMULSION DROPLET SIZE AND STABILITY USING CAPILLARY HYDRODYNAMIC FRACTIONATION

Miniemulsions comprising submicrometer oil droplets were characterized by size using capillary hydrodynamic fractionation. These miniemulsions were prepared by dispersing toluene in water using a mixed surfactant/cosurfactant system of sodium lauryl sulfate (SLS) and either cetyl alcohol (CA) or hexadecane (HD) and a high shear homogenizing device. Using this technique, the stability of various miniemulsion recipes was characterized by following changes in the average droplet diameter with time. In addition, this technique was used to directly compare the relative sizes of miniemulsions made with varying recipes and preparative techniques. The results of this study show that miniemulsion droplets prepared with cetyl alcohol as the cosurfactant decrease in diameter with increasing cetyl alcohol concentration. In addition, a period in which the droplet size increased rapidly was observed for these miniemulsions which was followed by a gradual size increase after about 60 min. This phenomenon was observed regardless of the homogenizing device used or how the cosurfactant was introduced. Miniemulsion droplets prepared using hexadecane as the cosurfactant were shown to be smaller than those prepared using cetyl alcohol, and these were shown to maintain their droplet size throughout the course of the measurements (a duration of 4 h). © 1994 by Academic Press, Inc.