Self-cleaning surfaces: the lotus effect

The natural model ...

The lotus flower (Nelumbo nucifera Gaertn.) is considered a symbol of purity in Asia. Its leaves unfold immaculately clean even from dirty water. Their leaf surface is not smooth, but microscopically rough - many small wax crystals cover the cone-like protruding (papillose) cells of the outer skin (epidermis). Plant species such as nasturtium, cabbage and Colocasia fallax Schott here in the Rainforest House also have similar leaf surfaces.

... how it works ...

Water does not find a good hold on such rough surfaces, because the bearing surface sinks. The wax additionally promotes detachment by its chemical properties. Therefore, drops roll off without wetting the leaf surface itself. On their way, they carry loosely adhering dirt particles with them. Every rain thus cleans the surface.

... and how we can use it

The principle of the self-cleaning surface has been transferred to many technical applications under the name Lotus-Effect, for example in textiles, facade paint, glass or special blow molds on blast furnaces.

Image captions

Water droplets on the leaves of lotus and Colocasia fallax do not wet the surface, but roll off as shimmering silvery spheres.

Electron micrograph of the leaf surface.

Dirt and water adhere well to smooth surfaces (left). On the rough leaves of the lotus, the beading water takes the dirt with it (right).

Text of the information board in the Botanical Garden