M. Porras

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

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 omega promote the necessary mixing level. However, results indicate that, if free oil remains together with liquid crystal formed during emulsification, a too high omega 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.

Preparation of Span 80/oil/water highly concentrated emulsions: Influence of composition and formation variables and scale-up

The influence of composition and preparation variables on the properties of W/O highly concentrated emulsions obtained in the system Span 80/oil/water was studied. Emulsions prepared with decane, dodecane and hexadecane were analysed. Stability of emulsions was found to depend on the oil as follows: stability of hexadecane emulsions > dodecane > decane. It was attributed to the lower solubility of water in the oil with longer chain. Experimental design tools were used to study the influence of composition and preparation variables and scale-up on the droplet size and polydispersity of emulsions formed. The most important factor was found to be the surfactant-oil ratio, SO, as more surfactant could stabilize more interface, but other preparation variables, like mixing rate, omega, were also found to influence the droplet size and polydispersity. The proper scale-up variables were found not to correspond to the dimensionless variables commonly used in scale-up studies, but total addition time, t(t), and angular mixing velocity, omega, seemed to be the proper ones.