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Superhydrophobic Surfaces
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On superhydrophobic surfaces, water droplets roll off even at inclinations of just a few degrees, taking up any contaminants encountered on their way. Therefore superhydrophobic, self-cleaning surfaces would be a great advantage in many applications. In nature, superhydrophobicity is conferred by surface roughness on the micro- and nanometer scale. In many methods proposed for making artificial superhydrophobic surfaces roughness is introduced by direct modification of the surface. Other procedures attempt to mimic the dual-scale roughness known from nature, such as the lotus leaf structure, by deposition of particles on the surface. |
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SEM image of a Lotus leaf visualizing its double scale roughness. A double scale roughness is also intrinsic to our hybrid core-shell partilces. They are prepared by growing silica nanoparticles on the PS surface and coating these with a permanent 10-30 nm thick silica layer (see particle synthesis). |
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Superhydrophobic coatings should be easy to make and apply, mechanically resistant, and long-term stable. None of the techniques existing so far fulfils all three of these criteria. By preparing superhydrophobic surfaces from dispersed raspberry-like silica particles with a polystyrene core, we get a step closer to this goal. When multilayers of particles are exposed to tetrahydrofurane (THF) vapour, polystyrene leaks out of the core, and bridges form between the particles, conferring mechanical stability. |
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The resulting continuous films are superhydrophobic with static contact angle for water of about 150-160° and roll-off angle of a few degrees. |
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Scanning electron microscopy (SEM) images of a film prepared by water evaporation, after THF and silane exposure. Lower right: high magnification SEM image showing bridge formation Upper top: Water droplet deposited on the superhydrophobic film. |
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| Contact: Doris Vollmer | |
