Influence of Composition Variables on the Molecular Diffusion from Highly Concentrated Water-in-Oil Emulsions (Gel−Emulsions)

Diffusion of mandelic acid (MA) molecules added to highly concentrated water-in-oil emulsion has been studied. Highly concentrated water-in-oil emulsions formed in pseudoternary water/nonionic surfactant/hydrocarbon systems (gel−emulsions) have been used as the releasing material. These emulsions have been enclosed in dialysis bags, and the release of MA added to the emulsion has been studied as a function of time. Factors that can influence the release like stability of the gel−emulsion and partition of MA between the internal and external phases of the emulsion have been studied. Gel−emulsions containing MA are less stable than those with this molecule absent. Addition of a longer chain surfactant to the system improves stability and reduces release rates. However, addition of electrolytes to the aqueous phase improves stability but increases the observed release rates. These facts have been shown to be due to changes in the partition coefficient of MA due to the salting-out effect produced by the strong electrolytes. The effect of dispersed phase fraction on the stability and release rates is also discussed.