Emulsion droplets with smaller droplets inside them - double emulsions - can be made in a controlled way using microfluidic devices, say Japanese researchers.   

Toru Torri and colleagues from the University of Tokyo have shown how microfluidic devices, which create droplets with uniform sizes, can be used to control the formation of water-in-oil-in-water and oil-in-water-in-oil double emulsions.   

Double emulsions have many potential applications, including controlled release of encased chemical substances, but difficulties in reproducing droplets of specific sizes limits their manufacture. 

Torri's group has devised a system where a stream of aqueous droplets forms within a flowing organic phase when the two phases meet at a T-junction. When this stream then flows into a second aqueous phase at another T-junction, the result is an aqueous phase containing organic droplets that in turn contain the original aqueous droplets (water-in-oil-in-water). 

If a cross-shaped junction is used two different substances can be trapped. The size and number of encased droplets is controlled by simply adjusting the liquids' flow speeds at each junction.   

Caroline Moore