Baby Bubbles

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Science  04 Feb 2011:
Vol. 331, Issue 6017, pp. 512-513
DOI: 10.1126/science.331.6017.512-d

Emulsions consist of droplets of one fluid immersed in a second, immiscible fluid and stabilized through the addition of surfactants or emulsifiers. Examples include oil and vinegar salad dressing and some cosmetics or perfumes. Over time, droplets may adhere together and form a cream or sediment, but this is a reversible process. Droplets can also irreversibly coalesce together or undergo Ostwald ripening whereby the largest droplets grow even larger at the expense of the smaller ones. In studying droplets smaller than 150 nm, formed by sonication, Delmas et al. find that droplet size evolution is an exponential function of the sonication time for a given sonication power but is not influenced much by surfactant concentration or type, or the viscosity of the samples. They are able to obtain a master curve correlating the average diameter to the sonication energy. For these small droplets, destabilization only occurs by Ostwald ripening, but this can be prevented by kinetic trapping of molecules in the droplet interiors or at the membrane between the two phases.

Langmuir 27, 10.1021/la104221q (2011).

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