When a drop of water falls off rapidly on the wing of an insect, a bird feather or leaf of a plant, there a shock wave, through which she quickly breaks into many small droplets, it is reported in the Proceedings of the National Academy of Sciences. This reduces the time of contact of the liquid with the surface and reduces the damage that moisture can cause the body. In previous studies, were evaluated as insect wings and similar surfaces interact with the slower drops.
For those who cannot wait out the rain in a warm house, as people, is a weather phenomenon sometimes poses a risk. If the animal gets wet, it will rapidly cool and may freeze. And small organisms, such as insects, rain can and does bring down to earth. To protect themselves from the falling water, the animals developed a variety of modifications of the integument: microscopic flakes or irregular protrusions on them repel water.
The mechanisms of hydrophobicity in living organisms are usually studied, dropping on them drop from a small height. But in nature, the rain may be rapid and strong, and in this case velocity will be much higher pilot — to 10 meters per second. For the butterfly the force from the impact of such a drop on the wing can be compared to the force that the bowling ball would hit the man falling from the sky. As such rain handle the integument of animals, was not very clear.
Staff at Cornell University under the leadership of Kim Sanho (Seungho Kim) has identified what happens when a rapid fall of drops on the leaf surface of plants (Cercidiphyllum japonicum), feathers of birds and wings of various butterflies and dragonflies. The samples surfaces were obtained from University Museum collections and from the nearest landing (in the case of plants). Water Lily on them from a height of two meters (the droplets had a radius of from 1.1 to 2 millimeters), and filmed on high speed camera.
It turned out that when a drop of water quickly (at a speed of 3.8 meters per second or more) drops on superhydrophobic wing, a feather or a leaf, appear the shock wave, it breaks on the ground and turns into significantly smaller droplets. Drops, whose speed did not exceed 0.9 meters per second, so it is not crushed.
Grinding drops reduces the contact time of water with the surface, whereby less heat is lost and reduces the force of impact. Apparently, the microscopic protrusions on the surface act on a drop like a needle to a balloon, and due to the nanoparticles of wax residual water quickly roll off the wing of a leaf or a feather.
Using this data, researchers have created a somewhat artificial superhydrophobic materials, which are rapidly falling drops too broke. However, they are still worse than biological, as it is not able to recover itself. Organisms constantly update their veils, through which their superhydrophobic surfaces are very long. How to recover micro – and nanostructure, superhydrophobic materials without the aid of living cells is not yet clear.
Biological structures often give the engineers ideas to create new devices and materials. So, inspired by the surface structure of the wings of a butterfly Pachliopta aristolochiae, scientists from Germany and the US have created a material that increases the efficiency of light absorption by solar panels.