S10.1-4  Tuesday, Jan. 7 09:03  The hairy, superhydrophobic surfaces on the water fern Salvinia – underwater air retention and raindrop impacts MAYSER, M.J.*; BARTHLOTT, W.; GILET, T.; University of Liege; University of Bonn; University of Liege m.mayser@ulg.ac.be

Superhydrophobic surfaces are of high scientific and economic interest because of their remarkable properties. Recently the immense potential of air-retaining superhydrophobic surfaces has started to be explored, e.g. for low-friction fluid transport and drag-reducing ship coatings. A major problem of superhydrophobic surfaces mimicking Lotus leafs is the limited persistence of the air retained, especially under rough flow conditions. However, a variety of floating or diving plant and animal species do exist. They possess hairy, air-retaining surfaces optimized for durable water-repellency. In particular, water ferns of the genus Salvinia have developed superhydrophobic surfaces that are capable of maintaining air layers for months.

Here the retained air volume of different Salvinia species is precisely measured and monitored over time. The rate of air loss is not necessarily proportional to the air-water interface area, but is also well correlated with the respective micro structure of different species. In a second set of experiments, we investigate the influence of the sophisticated hair architecture of Salvinia on raindrop impacts. Several regimes of rebounding, separation and splashing are observed for different drop sizes and impact velocities.