The Plant Cuticle: Multifuncional Interface and Model for Biomimetic Technical Surfaces

Christoph Neinhuis

Botanisches Institut und Botanischer Garten der Universität Bonn, Meckenheimer Allee 170, D-53115 Bonn, Germany

e-mail: unb11f@mailin.uni-bonn.de
 

The surfaces of plants are covered by a thin extracellular membrane, the cuticle. In many species, the cuticle is covered by characteristic microstructures formed by soluble lipids. They are usually called waxes and originate from self-organisation. Currently several principle ways are discussed how wax crystals emerge form the amorphous material that is transported to the cuticle surface. This wax layer represents a multifunctional interface between the plant and its environment influencing light reflexion, air flow and often causing high water repellency. While in smooth hydrophobic surfaces contact angles reach up to 110°, roughness in the dimensions of some micrometers causes nearly zero wetting with contact angles up to 170°. In such cases, the area for adhesion of water is minimized and air is enclosed between the droplets and wax crystals. And the same holds true for particles. Again, the contact area between particle and surface is minimized resulting in the adhesion of particles to water droplets that roll off the leaves. Independant of size and chemical nature, contaminations are removed from such evolutionary optimized surfaces with only a small amount of rain. Since this effect can be beautifully demonstrated on the leaves of the sacred lotus, the symbol of purity in Asian religions, we called it Lotus-Effect.

The Lotus-Effect depends only on the physico-chemical properties of the leaf surfaces. Therfore we initiated a joint project together with currently ten industrial companies to transfer the Lotus-Effect into products with biomimetic self-cleaning surfaces such as facade paints, roof tiles, polymers or paints.