Preparation of monodisperse particles and emulsions by controlled shear

Monodisperse emulsions can be obtained by applying a shear step to a crude polydisperse one [1]. In this paper, we first describe the mechanisms and conditions for the occurrence of this transformation. The fragmentation, process involves two distinct regimes. At short time (shorter than one second), the droplet diameter decreases abruptly. The droplets deform into long threads that undergo a Rayleigh instability. The obtained diameter is mainly determined by the applied stress and weakly depends on the viscosity ratio between the dispersed and continuous phases. However, this last parameter is determining for monodispersity. After this first step, the resulting droplets can, once again, break up into daughter droplets. This second mechanism is much slower, with a characteristic time of several hundred seconds, and much less efficient for fragmentation. A large variety of calibrated materials (direct, inverted, multiple emulsions and suspensions) can be obtained following this monodisperse fragmentation process.