Formation of water-in-oil (W/O) nano-emulsions in a water/mixed non-ionic surfactant/oil systems prepared by a low-energy emulsification method

W/O nano-emulsion formation by a low-energy emulsification method is described for the first time. The nano-emulsions have been formed in water/mixed Cremophor EL:Cremophor WO7 surfactant/isopropyl myristate systems at Cremophor EL:Cremophor WO7 ratios between 1:2 and 1:9, by slow addition of isopropyl myristate to surfactant/water mixtures. Phase behaviour studies have showed that the compositions giving rise to W/O nano-emulsions belong to multiphase regions, one of the phases being a lamellar liquid crystalline phase. The droplet size of the nano-emulsions at a fixed oil concentration of 85% and mixed surfactants/water ratio of 70/30 ranged from 60 to 160 nm as Cremophor EL:Cremophor WO7 ratio increased from 1:8 to 1:2. These nano-emulsions showed high kinetic stability. No phase separation was observed during 5 months in nano-emulsions of the water/Cremophor EL:Cremophor WO7 1:8/isopropyl myristate system with 85% oil concentration, although droplet size experienced an increase with time.