Effect of salt concentration on n-dodecane-in-brine nano-emulsions produced by phase inversion temperature method

Nano-emulsions are a class of very small and uniform nanometric-sized emulsions that can be defined as transparent or translucent liquid dispersions composed of water, oil and surfactants. They are kinetically stable with mean droplet diameters ranging from 20 to 1000 nm. Nano-emulsions can be prepared by a number of high and low energy processes. This study focuses on the preparation of nano-emulsions using one of the low energy methods known as phase inversion temperature (PIT) method which depends on the changes in the solubility of polyoxyethylene-type non-ionic surfactant with temperature. The surfactant is more hydrophilic at low temperatures and lipophilic at high temperatures. PIT point is a temperature in between at which condition the interfacial tension between the oil and water phases becomes extremely low leading to the production of emulsions with very fine droplets. The present work concentrates on the effect of salt concentration on oil-in-water nano-emulsions produced by PIT method using salt concentrations in the range from 0 to 0.1 M. NaCl and KCl were used as the salts. PIT points for the salt solution were found using conductivity measurements. The size distribution and polydispersity of droplets in nano-emulsions formed at PIT point were determined using dynamic light scattering technique. The results specify that both NaCl and KCl salts had no major effect on PIT points possibly due to the narrow salt concentration ranges used in this study. Also the changes in the size and size distribution of droplets with change in salt concentration were not significant within the range of salt concentration used in this study.