Lotus-Effect

The lotus effect refers to the very high water repellence (superhydrophobicity) exhibited by the leaves of the lotus flower (Nelumbo). Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface, which minimizes adhesion.

Due to their high surface tension, water droplets tend to minimize their surface trying to achieve a spherical shape. On contact with a surface, adhesion forces result in wetting of the surface. Either complete or incomplete wetting may occur depending on the structure of the surface and the fluid tension of the droplet. The cause of self-cleaning properties is the hydrophobic water-repellent double structure of the surface. This enables the contact area and the adhesion force between surface and droplet to be significantly reduced resulting in a self-cleaning process. This hierarchical double structure is formed out of a characteristic epidermis (its outermost layer called the cuticle) and the covering waxes. The epidermis of the lotus plant possesses papillae with 10 to 20 µm in height and 10 to 15 µm in width on which the so-called epicuticular waxes are imposed.

The hydrophobicity of a surface is related to its contact angle. The higher the contact angle the higher the hydrophobicity of a surface. All this leads to a self-cleaning effect.

Source: en.wikipedia.org/wiki/Lotus_effect 22.03.2012