The stability of N-Dodecane/brine nanoemulsions produced by phase inversion temperature method

Abstract

Nanoemulsions which exist between macroemulsions and microemulsions contain droplets with size ranging from 20nm to 200nm. Nanoemulsions are commonly used in cosmetics, foods, agrochemicals, etc due to their ultra-small droplet sizes and kinetic stablility. Among the techniques for producing nanoemulsions, phase inversion temperature (PIT) method was chosen to produce n-dodecane/brine nanoemulsions in this study because of the advantages of saving energy and surfactant. By the PIT method, nanoemulsions can be produced by heating the system close to the PIT point followed by a quenching process, because the solubility of polyoxyethylene-type nonionic surfactant changes with temperatures. This study focused on the effect of salt concentrations on the production and stability of O/W nanoemulsions since this effect has not been completely understood. The stability of the system was assessed by measuring the particle sizes and polydispersity index (Pdl) by dynamic light scattering as a function of time and temperatures. In the range of salt concentrations studied, we found that salt had no significant effect on PIT points and the initial droplets were in similar sizes and size distribution. The system without or with an optimum salt concentration, produced more stable nanoemulsions with lower Ostwald ripening rate compared to others. The most interesting part was that the ageing nanoemulsions could be reverted into their initial particle sizes and Pdl only in the system containing salt. The reversible process could be done by heating the ageing nanoemulsions to a temperature higher than the PIT point then cooling to their original storage temperature