Figure 1: Water droplets on a lady's mantle leaf.

Figure 2: SEM image of a "young" lady's mantle leaf. In average, the hair has a diameter of 10 µm, a height of 1 mm and an average distance of 500 µm.

Microreplication of biological surfaces

The water-repellency of biological systems has attracted a lot of interest in the last decade when W. Barthlott and C. Neinhuis described the phenomenon in detail for the lotus flower[1]. Water is completely repelled from the lotus leaves thereby removing all sorts of particulate contaminations such as dust, polls and toner[2].

The superhydrophobic effect of the lotus as well as of other plants results from the topography of the leaf, i.e. its combined micro- and nanoroughness.

A second category of plants which have a hairy surface also exhibit a strong hydrophobic behavior. For this type of plants S. Herminghaus et al. proposed a model where the elasticity of the plant hair accounts for the water-repellency of the leaf surface. As a representative the lady's mantle's surface has been closely investigated[3].

Our aim is to mimic the lady's mantle surface using polymer networks in order to systematically study the influence of elasticity and hair length and distribution on the hydrophobic effect. The process used involves two steps: the molding of an elastomer against an appropriate master (a metal mask or the leaf itself) and a subsequent polymerisation within the mask in order to generate the desired elastic polymeric model structure.

Literature:
[1] W. Barthlott, C. Neinhuis, Planta 1997, 202, 1.
[2] http://www.botanik.uni-bonn.de/system/bionik_flash.html
[3] http://www.uni-ulm.de.../pfohl/diplom_otten.pdf