MICROFLUIDICS

Breaking Up Is Hard To Do

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Science  29 Oct 2004:
Vol. 306, Issue 5697, pp. 781
DOI: 10.1126/science.306.5697.781a

Emulsions consist of droplets of one liquid encased within a second immiscible liquid and are important, for example, in the manufacture of cosmetics and foods. Double emulsions consist of droplets that encase finer droplets that are suspended in a continuous phase, such as water in oil in water. Double emulsions can be made using vigorous mixing techniques or by forcing single emulsions through membranes or nozzles, but in all cases a broad size distribution is obtained. Okushima et al. have turned to microfluidic devices, which have already shown a lot of promise in making droplets of controlled sizes using T junctions and variations in flow conditions. A series of T junctions where the properties of the channel changed at the junction were used to make double emulsions. To make water droplets within an oil phase, the junctions were designed so that water flowed into a hydrophobic channel, causing it to pinch off. This stream then flowed into a second hydrophilic channel, thus creating the double emulsion, with a very narrow distribution in the size of the droplets. With a slight adjustment of the flow conditions, it was also possible to encapsulate two water droplets from different sources within a single oil droplet, and by reversing the order of the channels they were also able to make oil-water-oil emulsions. —MSL

Langmuir 10.1021/la0480336 (2004)

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