Emulsification mechanism and storage instabilities of hydrocarbon-in-water sub-micron emulsions stabilised with Tweens (20 and 80), Brij 96v and sucrose monoesters

The influence of both the nature of the surfactant and surfactant concentration on the processes of droplet break-up and coalescence in the formation of decane-in-water nano-emulsions in a high-pressure homogenizer was investigated. Emulsions were produced using a Christison Scientific M110-S microfluidiser with an impinging jet high-shear chamber. For all six surfactants studied (Tween 20, Tween 80, Brij 96v, sucrose monolaurate, sucrose monomyristate and sucrose monopalmate), the droplet size decreased with increasing surfactant concentration reaching a limiting droplet size at a surfactant concentration of 15 mM. The limiting droplet size for the different surfactants used were; Tween 20 (approximately 250+/-30 nm), Tween 80 (approximately 320+/-40 nm), Brij 96v (approximately 200+/-20 nm) and the three sucrose monoesters had very similar sizes of approximately 250+/-20 nm. A hydrophobic fluorescent dye (1-undecylpyrene) was used to establish the extent of competition between droplet break-up and coalescence in the emulsification process. For all the emulsifiers studied, droplet coalescence in the process reduced as the amount of emulsifier increased, becoming zero at concentrations of about 15 mM, i.e. the same concentration as that required to produce the limiting minimum droplet size. This shows that in the emulsification process droplet size is determined by both break-up and re-coalescence events, and at lower surfactant concentrations (