Applied Physics

A Quick Freeze

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Science  22 Feb 2013:
Vol. 339, Issue 6122, pp. 885
DOI: 10.1126/science.339.6122.885-a
CREDIT: A. JAHN ET AL., LANGMUIR 29, 1717 (4 JANUARY 2013) © 2013 AMERICAN CHEMICAL SOCIETY

Microfluidics, in which small volumes of liquids are manipulated inside narrow channels, has proven to be a useful tool for the controlled fabrication of a range of materials. For example, through the delicate mixing of two fluid streams, it is possible to produce uniform oil-in-water emulsion droplets. Because the flow is laminar, it is also possible to create a long mixing layer at the interface between two miscible fluids. Cryogenic freezing has been used to capture or preserve fragile biological structures while minimizing ice crystal formation for subsequent analysis with an electron microscope. Jahn et al. extended this thinking to devise a technique for rapidly freezing a capillary stream as it exits the microfluidic device using jets of liquid propane. They studied the formation of nanometer-sized lipid membrane structures such as unilamellar vesicles, which are of interest because of the use of liposomes in cosmetics, pharmaceuticals, and food production. Through this process, they were able to capture both fully formed structures and their intermediaries. For the assembly of phosphocholines at the water and isopropyl alcohol interfaces, they observed disklike intermediate assemblies, consistent with current theories on the assembly process.

Langmuir 29, 1717 (2013).

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