Abstract Summary (Max 250 words)
Double emulsions (DEs) consist of a simple emulsion dispersed within a continuous phase, forming a two-compartment structure. They are widely used for encapsulation and controlled-release applications, such as in the pharmaceutical industry. Their preparation typically involves two steps, where the second step is mainly performed in batch devices (stirred tanks or rotor-stator, for instance). However, these systems exhibit highly non-uniform energy dissipation, often leading to broad droplet size distribution (DSD). In this study, a continuous alternative is proposed where the second step of preparation is carried out in open-cell solid foams (OCSF) used as static mixers. Thanks to their random structure and high porosity, these materials are cheap and result in reduced pressure drop and energy consumption, while promoting local drop deformation. Single-phase Computational Fluid Dynamics (CFD) simulations are carried out to compare their performance with that of SMX+ (a structured commercial static mixer). The simulations show that OCSFs generate high local shear and elongational rates, whereas the SMX+ mixer produces stronger overall energy dissipation. To connect local flow information with droplet-scale behavior, a population balance model accounting for the effects of both turbulence and elongation-induced breakage is employed to predict the DSD of these DEs. The influence of the operating conditions (flow rate of the continuous phase, mixer type) and the formulation parameters (oil viscosity, water fraction, etc.) on the DSD of water-in-oil-in-water DEs and their encapsulation efficiency is investigated. The results demonstrate that OCSF can achieve finer emulsions at lower energy cost.
