Most gardeners know that nasturtium leaves have an unusual resistance to water. When it rains the water collects in droplets and the leaf surface stays dry. Some butterfly wings offer the same resistance.
Recently, these surfaces have been found to have microscopic ridges, which increase the surface area and break-up rain-drops. JC Bird et al describe how this happens in this week’s Nature ( 21 November, 503, 385-388): drops bounce faster from the ridged surface so that water doesn’t retract symmetrically. This shortens the contact time between the drop and the surface.
Such hydrophobic materials are important not only in raincoats but when the icing-up of surfaces is a hazard, such as on aeroplane wings.
(T Whipple, The Times, Nov 22)
“We’ve demonstrated that we can use surface texture to reshape a drop as it recoils in such a way that the overall contact time is significantly reduced,” Professor James Bird said. “The surface stays drier longer if this contact time is reduced, which has the potential to be useful for a variety of applications.”
There is a prize for the author of the first posted comment that identifies the second and third pictures above.