|
|
Lotus effect
The Lotus-effect refers to the extremely small “wetability” and high self cleaning of biological surfaces, one example for this is the Lotus flower. On the bloom and the sheets even extremely bonding, colored powder is rinsed away by plain water, even water based adhesives are not able to stick to the surface. Other plants, as for example Reed and Bananas, show this effect too.
After the botanic-professor Wilhelm Barthlott of the University of Bonn stated that some plants were frequently dirty in the Herbarium, but other kinds remained always clean during many years, he examined this phenomenon more exactly and described its physicochemical basis, as well did C. Neinhuis in the 1990s.
The reason for the lotus effect lies in the special surface texture. It shows microscopically small cell collections, which are scattered with again even smaller crystals. This double structure causes an impressive physical effect - water drops which fall on the sheet form small beads due to the surface tension, then roll off and thereby carry away the contamination.
Opposite water contact angles of up to 160° are reached by the surface texture of the plants (they are super-hydrophobic). That means that only about 2 to 3% of the beads’ surface stays in contact with the surface of the plant, this means the surfaces possess an extremely small wetability. The adhesion between the surface and the water drop is so small that the water can flow away easily. Dirt particles resting on the surface also possess only a small contact area – they are rinsed away easily by the water flowing down.
Biological meaning:
The biological meaning of this effect for the plant lies in the protection against a settlement of micro organisms, pathogens or germs, for example mushroom pores, or the vegetation with algae. This is valid in similar way for animals as p.e. butterflies or insects which have legs that are not long enough to reach out over their whole body to clean themselves.
Application:
We are now able to copy the surface textures artificially. Nano-products are e.g. self-cleaning roofing tiles and self-cleaning facades. The treated surfaces are water-rejecting but not self-cleaning, they are only easy to clean.
|
|
