Chemistry

Drying and Wetting Droplets

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Science  06 Jul 2007:
Vol. 317, Issue 5834, pp. 18
DOI: 10.1126/science.317.5834.18c

Exploring the phase relations of complex solutions requires a convenient means of systematically varying the component concentrations. In this vein, Shim et al. developed a microfluidic system in which permeable membranes facilitate variation of the water composition of solute-containing droplets. Surfactant-stabilized aqueous droplets are formed in an oil stream, and the flat rectangular cross-section of the channels causes the droplets to adopt a disklike shape, so that their area changes with droplet volume. A droplet is then maneuvered into a region where the channel is connected to a reservoir via a poly(dimethylsiloxane) membrane. The reservoir can be filled either with dry air to shrink the droplet and concentrate the solute, or with water to expand the droplet and dilute the solute. This system was used to determine the aqueous phase diagram of poly(ethylene glycol) (PEG) and ammonium sulfate and to study regions of nucleation and growth of protein crystals (lysozyme) from solutions containing salts and PEG. — PDS

J. Am. Chem. Soc. 129, 10.1021/ja071820f (2007).

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