Electroacoustic Study of Concentrated Oil-in-Water Emulsions

Electroacoustics was used to study SDS-stabilized sunflower oil-in-water emulsions, with oil volume fractions between 2% and 50%. The dynamic mobility of the oil droplets was measured; the size and electric charge on the drops were calculated using formulas derived for dilute and concentrated systems and the results were compared. The relation derived for concentrated systems appears to be valid up to at least 50% provided the particles remain within the size range of the instrument, which shifts upward with rising concentration. Conductivity and pH had little effect on particle properties in the range studied; higher oil volume fraction (φ) had a substantial influence on the particle size produced in a homogenizer, but not on the zeta potential. Both median size and spread decreased with increases in φ. In contrast, both size and charge were hardly affected at volume fractions less than 10%. Dilution of the emulsion with a surfactant solution of the same composition as the water phase changed neither the particle size nor the zeta potential. The temperature of the emulsification process had a significant influence on the particle size but the zeta potential was hardly affected. Surfactant concentration had some effect on size at low volume fractions but not for φ>10%. The electroacoustic method hence could be applied to analyze both the dilute and the concentrated emulsions directly. Copyright 2001 Academic Press.