Formation of nano-emulsions by low-energy emulsification methods at constant temperature

Formation of nano-emulsions has been studied in the system water/Brij 30/de cane at 25 degreesC by three low-energy emulsification methods: (A) stepwis e addition of oil to a water-surfactant mixture, (B) stepwise addition of w ater to a solution of the surfactant in oil, and (C) mixing all the compone nts in the final composition. Nano-emulsions with average droplet size of 5 0 nn and high kinetic stability have been obtained only at oil weight fract ions, R, lower than 0.3 by emulsification method B. Independent of the oil weight fraction, R, emulsions obtained by method B have lower polydispersit y than those obtained by methods A and C. Phase behavior studies have revea led that compositions giving rise to nano-emulsions consist of W-m, (O/W mi croemulsion), L-alpha (lamellar liquid crystalline), and O toil) phases, at equilibrium. It has been shown that equilibrium properties cannot fully ex plain nano-emulsion formation. Low values of equilibrium interfacial tensio ns and phase equilibrium involving a lamellar liquid crystalline phase are probably required but not sufficient to obtain nano-emulsions in this syste m. The key factor for nano-emulsion formation has been attributed to the ki netics of the emulsification process. The change in the natural curvature o f the surfactant during the emulsification process may play a major role in achieving emulsions with small droplet size.