A common step in industrial cooling processes is the liquefaction of a vapor on a condenser. However, if a liquid film forms on the condenser, the cooling may be compromised. The problem can be addressed by coating the condenser with a hydrophobic material conducive to drop formation and then letting the drops slide off due to gravity. Chuan-Hua Chen of Duke University and his student Jonathan Boreyko now report a different approach. By depositing carbon nanotubes on silicon micropillars and coating both with hexadecanethiol (C16H34S), they engineered a rough “superhydrophobic” surface. The water drops that condensed on it were about a hundred times smaller than those on a conventional hydrophobic surface that the Duke team considered as a standard; the surface roughening offers the promise for more efficient cooling. Furthermore, as the figure and online video show, when two sufficiently large drops coalesce into a single...

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