Influence of Disperse Phase Transfer on Properties of Nanoemulsions Containing Oil Droplets with Different Compositions and Physical States

Abstract

The impact of the initial oil droplet composition and physical state on molecular exchange processes in mixed oil-in-water nanoemulsions was investigated. Nanoemulsions consisting of model oils (hexadecane or octadecane), non-ionic surfactant (Tween 80), and water were prepared by microfluidization. The physical state of the droplets in the nanoemulsions was varied by altering their thermal history. The evolution of oil droplet size and composition during storage was monitored using dynamic light scattering and differential scanning calorimetry, respectively. The effects of oil phase composition were examined by preparing nanoemulsions containing liquid hexadecane droplets and liquid octadecane droplets mixed together at mass ratios of 100:0, 75:25, 50:50, 25:75 or 0:100 H:O (w/w). Changes in droplet growth and composition during storage depended on the initial mixing ratio of the two kinds of droplets. The higher the proportion of hexadecane droplets present, the faster the rate of droplet growth, which was attributed to its higher water-solubility. The final droplet composition depended on the initial ratio of the different droplets. Second, the impact of droplet physical state was examined by preparing nanoemulsions containing liquid hexadecane droplets and either liquid or solid octadecane droplets. The solidification of the octadecane droplets retarded molecular exchange, but promoted droplet growth in the mixed nanoemulsions. These results may have important implications for understanding molecular exchange processes in complex colloidal dispersions that contain multiple types of oil phase.