Microscopic View of How Leaves Repel Water 33
An anonymous reader writes: Years of research has gone into products that are hydrophobic — they resist getting wet. But nature solved this problem long ago, and it's ubiquitous outside our buildings and homes. You've probably seen it yourself, after a light rain: water collects in round droplets on many leaves from trees and plants, refusing to spread out evenly across the surface. This article explains why that happens using super slow-mo cameras and an electron microscope. "[T]he water isn't really sitting on the surface. A superhydrophobic surface is a little like a bed of nails. The nails touch the water, but there are gaps in between them. So there's fewer points of contact, which means the surface can't tug on the water as much, and so the drop stays round. ... [After looking at a leaf in the electron microscope,] we saw this field of tiny wax needles, each needle just a few microns in length! The water drops are suspended on these ultra-microscopic wax needles, and that keeps it from wetting the surface."
Sunlight and Water Myth (Score:5, Interesting)
Two years ago, four Hungarian scientists published a paper called “Optics of sunlit water drops on leaves: conditions under which sunburn is possible” in the journal New Phytologist. Given the near-universal belief that water drops can scorch plant leaves on a sunny day (e.g. the RHS book How To Garden: “Under a hot midday sun, water droplets on leaves will act as miniature magnifying glasses and may scorch them”), you may be surprised — or you may not — that no one had previously checked to see if this actually happens.
First of all, the short answer is no.
Are there any circumstances under which water drops on leaves can cause sunburn? Yes, but only if the leaf has a dense covering of water-repellent hairs, in which case drops can be held above the leaf surface, allowing them to focus light on the surface itself.