Properties of water-in-oil (W/O) nano-emulsions prepared by a low-energy emulsification method

Properties of water-in-oil (W/O) nano-emulsion formed by a low-energy emulsification method are described in this work. Nano-emulsions have been formed in water/mixed non-ionic surfactant/decane. Several mixtures of Span 20, Span 80, Tween 20 and Tween 80 were studied. Phase behavior studies and stability studies allowed to determine zones where nano-emulsions can be formed. Bluish and transparent W/O nano-emulsion with droplet sizes as low as 30 nm was formed. Nano-emulsion droplet size was measured by Dynamic Light Scattering. Nano-emulsions stability was studied by multiple light scattering and by dynamic light scattering. The results showed the evolution with time of the average radius droplet. The nano-emulsions prepared showed high kinetic stability for weeks, without phase separation, sedimentation or creaming. Nevertheless, their droplet size increased slightly over time. Stability studies show that nano-emulsion breakdown could be attributed to Ostwald ripening and coalescence mechanism, depending on the water concentration.