The formulation and stability of water-in-oil-in-water emulsions

Date of Completion

January 1997


Health Sciences, Pharmacy




The film strength of single ((Spans$\sp\circler$ (20, 80, 83 and 85), and Tweens$\sp\circler$ 20 and 80)) and mixed (Span$\sp\circler$-Tween$\sp\circler)$ emulsifier systems typically used in multiple emulsion formulations, were determined. Film strength was evaluated by interfacial elasticity measurements using an oscillatory ring surface rheometer at a model planar mineral oil/water interface. Interfacial elasticity was evaluated as a function of bulk concentration (1-5% w/v), presence of electrolytes in the aqueous phase (0-1M NaCl) and temperature (25-50$\sp\circ$C). Interfacial elasticity measurement provides information on interfacial rigidity which is related to film strength and hence to emulsion stability to coalescence and rupture. Emulsion stability was evaluated by phase separation for W/O emulsions and by release studies, photomicrography and droplet size analysis for W/O/W emulsions.^ Spans 20, 80 and 83 films exhibited appreciable elasticity (753.17 $\pm$ 0.00, 683.10 $\pm$ 29.13 and 1128.09 $\pm$ 14.81 mN/m, respectively at 5% w/v at 60 mins) whereas Span 85 films exhibited low elasticity (11.10 $\pm$ 3.88 mN/m at 5% w/v at 60 mins) and the Tween films did not exhibit any elasticity (0.1-5% w/v). The interfacial elasticities of Spans 20, 80 and 83 films increased with increase in bulk concentration and were influenced by temperature and the addition of electrolytes. The interfacial elasticities of the Span films decreased considerably with increase in Tween concentration in the aqueous phase. The film strength of the single and mixed surfactants at the primary W/O and secondary O/W interface of a W/O/W emulsion was shown to influence emulsion stability. Relatively stable W/O and W/O/W emulsions were obtained with emulsifier systems which exhibited high interfacial elasticity.^ Span-cholesterol-Tween and Span-protein mixtures were investigated to enhance film strength at the secondary interface. These systems were determined to be limited in their application to improving multiple emulsion stability owing to their low interfacial elasticity and the inability to reduce interfacial free energy respectively.^ Coacervation of the multiple oil droplets was investigated as a novel and practical approach to stabilizing W/O/W emulsion systems. Gelled or powder multiple droplets using gelatin/alginate complex coacervation were prepared which can be stored as such and then reverted to liquid W/O/W emulsions on administration. ^