Technology offer: The “raspberry-lotus” effect – stable, water-repellent and self-cleaning surfaces
Solar modules with no dust layer, clean windscreens, spectacles that never need to be cleaned – water-repellent surfaces that use the lotus effect and are self-cleaning can be used in a wide variety of applications. An invention by the Max Planck Institute for Polymer Research now enables the production of transparent and stable surfaces on which water forms droplets that drip off and remove dirt particles in the process – with the help of so-called “raspberry particles”.
The new process, for which a patent has been filed, is based on small electrostatically charged polystyrene balls studded with tiny glass particles. These balls, whose form is reminiscent of raspberries, are heated so that their polystyrene cores melt, leaving behind only the porous glass balls. The tiny “raspberries” are then applied to a corresponding substrate with the help of electrostatics. The resulting surface is comparable with the microstructure and nanostructure of the lotus plant. Water cannot adhere to this porous surface so it forms droplets and runs off. In this way, surfaces can be produced that not only repel water but that are also self-cleaning. Moreover, thanks to the new production process, these surfaces, which can also be transparent, are very stable mechanically and resilient. They can therefore be used on the surface of solar modules that, owing to rain, sun and wind, are exposed to severe environmental conditions. Their use as coatings for skyscraper façades which would not attract dirt is also conceivable.
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