Self-cleaning surfaces: the Lotus-Effect

The structural base of the self-cleaning effect is a combination of water-repellent material, the waxes, and a corresponding micro- and nanostructure. In the case of the lotus flower, the surface structure is finely knobbed, defined by epidermal cell with a size of 20–50 µm and wax crystals with a size of about 0,5–3 µm. Droplets of water flow together and form a spherical shape on the unwettable, finely knobbed surface of the leaves. The faintest shake or a slight incline will cause the water to roll off. Because of the small contact angle on the rough surface, even dirt particles hardly stay attached. If a drop of water is moving over the surface, it takes up dirt particles and removes them while rolling off the leaf. On a smooth surface, the drops of water disperse and “creep” around dirt particles, without taking up the dirt.

In 1987, Wilhelm Barthlott revisited his earlier observations and – together with his collaegue Christoph Neinhuis – analyzed the physico-chemical base of the “Lotus-effect®”, understood its significance in biological terms and produced an articificical surface that works on the same principles. In collaboration with several industrial partners, things like façade paint, roof tiles and non-optical glass with Lotus-effect^® have been introduced to the market. The possible range of application is indeed far-reaching. This example illustrates how basic research can yield practical outcomes.

Surface with Lotus-Effect®		Smooth Surface ("easy to clean")
Compete cleaning of the surface.		Dirt will only be smeared over the surface.

More information at: http://www.nees.uni-bonn.de/lotus/de/lotus_effect_html.html