Particle size reduction of emulsions by formulation design. I: Effect of polyhydroxy alcohols.

The objective of this study was to characterize the effect on particle size and stability of oil-in-water emulsion formulations caused by the addition of polyhydroxy alcohols. Stable soybean oil and hexadecane emulsions were prepared containing increasing amounts of propylene glycol (PG) and glycerol (GLY). A nonionic emulsifier system consisting of Tween 80 and Span 80 was used to achieve optimal stability. Particle size was found to decrease as the level of PG or GLY increased. A three-fold particle size reduction was obtained at a PG level of 40% w/w and at a GLY level of 70% w/w. The particle size of soybean oil emulsions decreased from about 4.8 microns to about 1.7 microns. The particle size of hexadecane emulsions decreased from about 2.7 microns to less than 1 micron. The increase in emulsion viscosity was found to be proportional to the amount of polyhydroxy alcohols added to the formulation. The particle size and creaming stability of the emulsions were found to improve with increasing PG or GLY concentration.