Water that does not wet

2001/06/21 Roa Zubia, Guillermo - Elhuyar Zientzia

• Fisika

When the water drops fall in a dry pan they have a very curious behavior. They have a movement similar to that of the mercury droplets, that is, they do not wet the lower surface or lose matter in the path. From a physical point of view, they have no interaction with the skin.

That was what scientists wanted to get. Although they move on any material, they intended that the drop of water would not leave a mark. This effect would be very useful for both practical applications and theoretical research.

The dynamics of water drops have been studied for a long time. This type of studies on the physics of liquids can serve, among others, to study the stability of stars and planets. This scope is also related to metal refining processes and cell movement.

If by geometry there were no interaction between a drop and the surface that sustains it, the angle indicated in the image would be 180º. With conventional methods it is very difficult for this angle to exceed 120º.

So far, to achieve this effect, the underlying surface was treated with a number of chemical substances, but this method was not successful if the skin was not kept completely clean. In nature, in the leaves of some plants this effect occurs and the drops of water slip quickly until their fall. The leaves are not usually humid, but to achieve it the skin needs a very complex structure. Nature has been designing this surface for years.

The journal Nature has published today a method to artificially create this effect. A group of French physicists has achieved this through another strategy. Instead of treating the skin, they decide to treat the liquid itself.

When adding to a drop of water the spores of the Lycopodium moss, the liquid remains itself covered by a hydrophobic layer. The drops then adopt the position of a small sphere and the angle increases to 180. The balls thus formed, in addition, act as a solid stranger.

It is a flexible solid drop, with high surface tension, which bounces and rolls without losing matter. When moving, being in liquid state, the internal matter is reorganized until it takes the form of a peanut and begins to rotate freely. In this way it makes very fast movements.