Droplet production methods

The first droplet production method described in the review is the droplet generation batch method.

The most common batch method can be performed as simply as by mixing water and oil in a jar and shaking it thoroughly. The resulting mixture of two immiscible fluids termed “emulsion” will disappear over time due to destabilizing phenomena (coalescence, Ostwald ripening).

The instability can be avoided by several means:

By adding amphililic molecules or surfactants to one of the two immiscibles phases to reduce the interfacial tension between the two phases.
By generating monodisperse droplets forming the emulsion to prevent Ostwald ripening.
By adjusting the rheological properties of the two phases (continuous & disperse) such as the viscosity.
At bigger scale, the process of mixing two immiscibles fluids can be performed with high-shear mixers. High-shear mixing still induces emulsion instability due to the lack of control over the resulting droplet size. Since two decades, microfluidics has slowly taken over the use of high-shear mixers for droplet batch methods to generate highly monodispersed droplets and to fabricate stable emulsions for many fields of application.

Droplet production methods: microfluidics