(349i) Nanoemulsion Formation: Controlling and Predicting Droplet Size
Nanoemulsions are liquid-liquid dispersions with droplet sizes on the order of 100 nm. They are used in diverse areas like drug delivery, pharmaceutics and development of smart food drinks, and possess exceptional properties such as high surface area, robust stability and tunable rheology. However, there is little knowledge in literature about the factors dictating the droplet size of nanoemulsions. In this work, we highlight that the droplet size correlations for macroemulsions (droplet size ~ 100 um) cannot be extrapolated to nanoemulsions. Hence, we derive a new criterion for predicting droplet size of nanoemulsions that takes into account the physics at small length scales. 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. Lastly, we also obtain a parity plot for the kinetic droplet size data prepared with different oil viscosities and different power density input. The proposed scaling theory and models are useful for rational design of nanoemulsions.