Formation and stability of n-dodecane nanoemulsions produced by the PIT method: effects of oil concentration and type of surfactant

Abstract

In this paper, the effects of sodium chloride on the formation and stability of n-dodecane/surfactant/NaCl/water nanoemulsions are discussed in terms of oil concentration (R) and the type of surfactant. Nanoemulsions, widely used in cosmetics and pharmaceuticals industries, are a dispersion system consisting droplets with sizes ranging from 20 to 200nm. Among the low energy methods, phase inversion temperature (PIT) method was used to prepare nanoemulsions by heating an emulsion system to a temperature close to PIT point followed by a quenching process as it works with the changes in affinity of a non-ionic surfactant with temperatures. Phase inversion process was determined by plotting the conductivity of emulsions versus temperatures. The change of the phase inversion process and the decrease of the PIT temperature, with increasing oil concentration, were more significant in brine system especially at high salt concentration. At low surfactant concentration, the nanoemulsions were monodispersed in either pure water or brine system, when R was 0.2 to 0.4. More sodium chloride was needed to produce stable nanoemulsions when the oil concentration was increased, viz. 0.001M NaCl in R=0.3 and 0.01M NaCl in R=0.4. When the oil concentration was increased, there was partial reversible system in low salt systems but irreversible system in high salt systems. In both pure water and brine system, nanoemulsions formed with mixed surfactant (Span80/Brij30) were polydispersed and had larger droplet size compared to n-dodecane/Brij30 systems. The mixed surfactant system was extremely unstable and there was no reversibility ability.