(444e) Nanoemulsion Formation: Controlling and Predicting Droplet Size
Nanoemulsions contain droplets of oil in water or water in oil with sizes on the order of 100 nm, and due to attractive properties such as high surface area, robust stability and tunable rheology, they are used in drug delivery, cosmetics, pharmaceutical formulations and development of smart food drinks. However, the literature uses relations for droplet size correlations developed for large emulsion droplets (or macroemulsions) in an ad-hoc manner without considering the effects of small droplet sizes. Here, we highlight that the droplet size correlations for macroemulsions (droplet size ~ 100 um) cannot be extrapolated to nanoemulsions, and hence derive a new criterion for predicting droplet size of nanoemulsions. The new scaling relation takes into account the effect of viscosity of droplet phase as well as continuous phase. We validate our scaling theory with a wide range of experimental droplet size data. Further, building on the proposed scaling theory, we propose a new breakage model for predicting the frequency of successful droplet breakup event, the rate-controlling step in nanoemulsion formation. A population balance analysis with the proposed breakage model provides insights about the kinetics of droplet size change and successfully captures the effect of droplet viscosity, unlike the earlier breakage models. The predictions of the proposed breakage model are supported by the experimental droplet size data. The proposed scaling theory and models are useful for rational design of nanoemulsions.