A principle of fluid flow is that the bottom-most molecules of a liquid stick to the surface of the solid they are sliding past — creating friction that, for instance, slows down water flowing through a pipe.
Choongyeop Lee at the University of California, Los Angeles, and his colleagues created textured surfaces with micrometre-scale grooves and posts. On these, fluids can slip past friction-free for tiny distances, coasting on the pockets of air between the grooves or posts. They report a slip length for water almost ten times longer than previously achieved — long enough, they suggest, to show that engineered surfaces can significantly reduce drag in fluid systems.
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Fluid dynamics: Slip and slide. Nature 454, 920 (2008). https://doi.org/10.1038/454920d