A miniemulsion is a special case of emulsion. A miniemulsion is obtained by shearing a mixture comprising two immiscible liquid phases, one surfactant and one co-surfactant (typical examples are hexadecane or cetyl alcohol).
The shearing proceeds usually via ultrasonication of the mixture or with a high-pressure homogenizer, which are high-shearing processes. In an ideal miniemulsion system, coalescence and Ostwald ripening are suppressed thanks to the presence of the surfactant and co-surfactant, respectively.
Stable droplets are then obtained, which have typically a size between 50 and 500 nm. The miniemulsion process is therefore particularly adapted for the generation of nanomaterials. There is a fundamental difference between traditional emulsion polymerisation and a miniemulsion polymerisation. Particle formation in the former is a mixture of micellar and homogenous nucleation, particles formed via miniemulsion however are mainly formed by droplet nucleation.