Formation of stable hydrocarbon oil-in-water nanoemulsions by phase inversion composition method at elevated temperature

Abstract

Stable hydrocarbon oil (hexadecane, C16)/nonionic surfactant (HCO-60, Span 80)/water system oil-in-water nanoemulsions were prepared by the phase inversion composition method at elevated temperature. To minimize droplet size, the composition ratio for stable nanoemulsions, we experimented by changing the HLB value, oil/surfactant ratio, and droplet volume fraction. When the HLBmix value 11, the nanoemulsions show a minimal sample droplet size of 360.3 nm. By varying the oil/surfactant ratio from 0.6 to 1.4, we found the optimum oil/surfactant ratio to be approximately 0.6, which corresponds to the minimum droplet size of 71.8 nm. We also varied the droplet volume fraction; when the droplet volume fraction is 0.06, the droplet size is very small. For the emulsion with the minimal droplet size, the polydispersity index is less than 0.3, which reflects a good monodispersity of the nanoemulsion. Viscosity and electrical conductivity measurements were carried out for determining the internal structure of the bicontinuous phase during the emulsification. When the water content ranges from 4 to 6 w/w%, the systems may have a bicontinuous or lamellar phase. Oil-in-water nanoemulsion stability assessment was performed by observing the droplet size as a function of storage time; we did not observe any change in droplet size over the course of a month.