#surfactants

Condensation-Based Method Could Create Stable Nanoscale Emulsions

Researchers at MIT have developed a condensation-based method that could create stable nanoscale emulsions.

The reluctance of oil and water to mix together and stay that way is so well-known that it has become a cliché for describing any two things that do not go together well. Now, a new finding from researchers at MIT might turn that expression on its head, providing a way to get the two substances to mix and remain stable for long periods — no shaking required. The process may find applications in pharmaceuticals, cosmetics, and processed foods, among other areas.

The new process involves cooling a bath of oil containing a small amount of a surfactant (a soap-like substance), and then letting water vapor from the surrounding air condense onto the oil surface. Experiments have shown that this can produce tiny, uniform water droplets on the surface that then sink into the oil, and their size can be controlled by adjusting the proportion of surfactant. The findings, by MIT graduate student Ingrid Guha, former postdoc Sushant Anand, and associate professor Kripa Varanasi, are reported in the journal Nature Communications.

As anyone who has ever used salad dressing knows, no matter how vigorously the mixture gets shaken, the oil and the vinegar (a water-based solution) will separate within minutes. But for many uses, including new drug-delivery systems and food-processing methods, it’s important to be able to get oil in water (or water in oil) to form tiny droplets — only a few hundred nanometers across, too small to see with the naked eye — and to have them stay tiny rather than coalescing into larger droplets and eventually separating from the other liquid.

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