The lotus is an Asiatic aquatic plant known for the superhydrophobic behaviour of its leaves. What does superhydrophobic mean? It means that the leaves do not get wet as they repel water.

When the rain droplets touch the lotus leaves they remain spherical which allows the droplets to bounce around until they fall off the leaf which stays dried. This phenomenon carries out other advantages as when droplets run through the surface they pick up the dust that accumulates on top, leaving the leaves completely cleaned as well as dried. This self-cleaning effect is called lotus effect alluding to this wonderful plant but it can be also found in other plant species, birds and even insects.

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This phenomenon has aroused great interest for its numerous potential applications in self-cleaning materials and in many different fields. A deeper knowledge on how this surfaces attain superhydrophobicity is key to copying and reproducing this natural effect in for example, glasses for windows, clothes, etc…

lotus

If we take a look at the lotus leaves under the microscope we will see a very distinctive surface, built up in 2 levels: tiny bumps can be seen in a microscopic scale, and on its tips a second level is formed by thin nanometric wires. Furthermore, this structure is covered with a waxy layer that increases the hydrophobic effect. This doble structure underpins water dropplets that maintain their spherical shape and the waxy layer favours the rolling of the droplets without wetting the leaf surface.  Therefore, is the combination of the physical and chemical effects what allows to affirm that lotus leaves are superhydrophobic.

Hierarchical structures

The most common way to achieve this self-cleaning materials nowadays is by using coatings that provide hydrobocibic properties to the surface in which are applied. But nanotechnology is right now becoming more important in this matter, since it allows a perfect reproduction of the doble structured observed in lotus leaves, this means that coating can be replaced by nanostructures avoiding for example adhesion problems of coatinga,  chemical pollutants management , loss of coating due to the use and time, etc… It is a step forward in the matter, in continuos improvement.