An original continuous process for double emulsions preparation using static mixers: Focus on the viscosity

Abstract

A novel method for the preparation of water-in-oil-in-water (W/O/W) double emulsions is proposed and evaluated in this work. It is based on the classical two-step method in which the inner water-in-oil (W/O) emulsion is prepared using a high shear device (first batch step). This inner emulsion is then dispersed continuously in an aqueous phase using in line static mixers as second emulsification step for the formation of double emulsions. This somehow semi-continuous preparation method is evaluated when varying the viscosity of the three phases (from 1 to 100 mPa s) and the internal aqueous phase fraction (from 1 to 40 wt %). Under the investigated conditions, the use of static mixers is shown to be efficient for the formation of double emulsions with monomodal droplet size distributions and high encapsulation efficiency despite the shear thinning behavior of the inner emulsions. A correlation was established to relate the viscosity of the inner (W/O) emulsion with the fraction of the inner phase, that was found to be independent of the viscosity of the inner water phase. Moreover, it was possible to control the range of variation of the droplets size of the double emulsion from some tens to hundreds of micrometers while the residence time is less than a second. This fast and efficient double emulsion preparation process constitutes a promising alternative to classical batch processes.