Microstructured devices for preparing controlled multiple emulsions

The preparation of multiple emulsions with controlled droplet sizes and internal structures has been a challenge for a long time. However, in recent years, a major breakthrough has been achieved in the preparation of monodisperse single emulsions by small-scale fluid processing, which has enabled the formation of multiple emulsions with the desired droplet sizes, structures, and compositions. This review deals with the preparation of controlled multiple emulsions in various microstructured devices. The four preparation pathways are discussed individually. They are (a) membrane emulsification, (b) microchannel emulsification, (c) the use of a two-dimensional microfluidic device, and (d) the use of a three-dimensional coaxial microcapillary device. The applications of the prepared multiple emulsions to a novel class of materials are also discussed.