Non-aqueous emulsions: hydrocarbon-formamide systems.

There are few reports in the literature on formulation of non-aqueous emulsions. This study was designed to evaluate some design criteria for such systems. Formamide is the closest polar solvent that has the ability to replace water in emulsification when employing established non-ionic surfactants as stabilisers. For the majority of studies, linear alkanes (C6-C16) were dispersed in formamide as the continuous phase were stabilised with polysorbate 20. Initial studies involved gentle emulsification and observing mean globule size. The mean globule size varied in a non-linear fashion with alkyl chain length, the minimum being between C10 and C12. Sonication for 30 s led to smaller differences in the mean globule size. The effect of various parameters such as surfactant concentration and solvophilicity of the surfactant was observed. The surface activities of polysorbate 20, 40, 60 and 80 in formamide and critical micellar concentrations were determined. The latter were several orders of magnitude higher in formamide than in water, and the areas per molecule larger. The addition of water to the dodecane formamide systems did not destabilise the emulsion. Release of the model drug dehydroepiandrosterone from dodecane in formamide emulsions was studied in distilled water, the rate of release being dependent on the volume fraction of dodecane.