High-order multiple emulsions formed in poly(dimethylsiloxane) microfluidics.

Multiple emulsions are nested sets of drops. Drops of one kind of fluid are encapsulated inside drops of a second fluid, which themselves can be encapsulated inside drops of yet another fluid. Such ‘‘emulsions within emulsions’’ are very useful for many applications, including for the encapsulation of actives, such as nutrients, pesticides, drugs, and detergents, and as templates for the synthesis of colloids with structured interiors. Multiple emulsions are typically made in bulk using shear cells or porous membrane plates. To form the multiple emulsions, the drops from one emulsification are fed back into the apparatus with additional fluids and are emulsified again. Such methods can form large quantities of drops very rapidly; however, the individual drop formation is poorly controlled. This produces some double emulsions but they are exceedingly polydisperse. For higher-order multiple emulsions, such as triple emulsions or quadruple emulsions, the excessive polydispersity makes the methods impractical. With glass microcapillary devices, monodisperse multiple emulsions can be formed with controlled structure, albeit in much smaller quantities. As opposed to bulk methods in which many drops are formed in parallel with little control, in microcapillary devices, drops are formed individually with a high degree of control. However, the glass devices are difficult to fabricate, requiring the hand alignment of separate microcapillary tubes. This is labor intensive and makes the devices difficult to scale up sequentially for producing higherorder multiple emulsions or in parallel for producing larger quantities. A superior method would combine the control of microfluidic drop formation with increased scalability. In this paper, we present a simple system to form monodisperse high-order multiple emulsions. This method combines the control of microfluidic drop formation with the