The mystery of how superhydrophobic lotus leaves remain completely dry whilst floating on water has been solved by Chinese scientists.

The top of a floating lotus leaf is a famous example of a superhydrophobic surface that sheds water, and has been used as a model for technologies such as self-cleaning windows. The leaf is covered in a rough surface of waxy projections, which causes water to form beads and slide off. Now Lei Jiang of the Chinese Academy of Sciences in Beijing and colleagues have found out why, when floating, no water flows onto the leaf.

Electron microscopy showed that, close to the leaf edge the projections are replaced by a smooth surface of folds and grooves, preventing the reverse-flow of water droplets. This means that the leaf is 50% more resistant to submersion than a model leaf with a smooth surface.

Jiang suggests that, just as the lotus leaf surface has provided inspiration for superhydrophobic surfaces, the leaf margin can serve as a model in applications such as tubes or microfluidic channels which require clean outflow or directional repellancy.

Abraham Marmur, a professor of water science and technology at Technion-Israel Institute of Technology, Haifa, says that 'the authors should be congratulated for opening a new angle for looking at the wonders of the lotus leaf'.

Michael Townsend