Biological and biomimetic materials and surfaces

From everyday life experience, we all know that during watering or rainfall, water rolls off the leaves of many plants in the form of spherical droplets leaving the leaves themselves entirely dry. This effect can be seen in an especially impressive manner on the leaves of the sacred lotus (Nelumbo nucifera) and Tropaeolum (Tropaeolum majus). Interestingly, with the rolling off of water droplets, dirt particles as well as fungus spores and bacteria are also very efficiently removed from the leaf surfaces as they are more tightly attached to the water droplet than to the leaf surface. The reason for this physicochemical “self-cleaning behaviour” is the double-structured water-repellent surface of the plant leaves which is comprised of microand nanostructured wax on dome-shaped papillose epidermis cells. Dirt particles as well as microorganisms and fungus spores are attached only via a few contact points to the leaf surface which has a micro-/nanoscale roughness. The same holds for the water droplets which become spherical for energetic reasons and cannot wet the leaf surface [1-3].