Nano-emulsions prepared by the phase inversion composition method: Preparation variables and scale up

Abstract

The aim of this work is to study, through experimental design, the effect of vessel geometry and scale-up in the properties of nano-emulsions prepared through the phase inversion composition method (PIC). Results show that a proper mixing is crucial for small droplet-sized nano-emulsions, especially when remaining free oil is found together with the key liquid crystal phase formed during the emulsification process. In these cases, mixing must be near the perfect mixed model. Proper geometries must be selected to promote a good mixture. Small addition rates V ad and high mixing rates ω promote the necessary mixing level. However, results indicate that, if free oil remains together with liquid crystal formed during emulsification, a too high ω could promote coalescence of oil droplets. When a cubic liquid crystal phase Pm3n is formed instead during emulsification, without free oil, coalescence is not promoted, probably due to the extremely high viscosity. For the system where Pm3n is formed during emulsification, scale-up cannot be done, as it would be expected, maintaining adimensional variables – Reynolds, Re, and adimensional time. A perfect correspondence between scales is observed when the total addition time and the lineal mixing rate are maintained between scales instead. Re, i.e. the ratio between inertial and viscous forces, does not seem adequate to describe the system, as inertial forces are worthless due to the extremely high viscosity.