Colloidal silica has been used to prepare both water-in-oil-in-water (w/o/w) and oil-in-water-in-oil (o/w/o) multiple emulsions. Because the destabilisation caused by surfactant diffusion has been eliminated, the multiple emulsions described are highly stable and show no variation in secondary emulsion droplet size over a 6 month period. The 1° w/o emulsion for the w/o/w emulsion was prepared using a hydrophobic silica (Wacker HDK H2000). Hydroxypropyl cellulose was added to the dispersed aqueous phase to reduce the droplet size and to improve monodispersity. Ludox HS-40 was then used in the secondary emulsification to prepare the w/o/w emulsion. A mixture of NP30 and NP6 was used as the costabilizer, the latter surfactant being added to reduce the inter-facial tension. In a similar way the 1° o/w emulsion for the o/w/o emulsion was prepared using hydrophilic silica (Ludox HS-40) and NP30 as a costabilizer. The secondary emulsification to prepare the o/w/o emulsion was effected with HDK H2000 silica.
Rheological measurements indicated 100% multiple emulsion yield up to an internal emulsion volume fraction of 0.4 for the w/o/w multiple emulsion and 0.6 for the o/w/o system.