Ice-free wings by nanostructuring

New surfaces repel water and prevent ice formation

Thermographic image of a strongly undercooled, still liquid drop of water on a plasma-functionalized nanostructured film. Fraunhofer IGB
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Fraunhofer researchers have developed nanostructured surfaces on which water is repelled and virtually no ice forms even at freezing temperatures. In the future, they can be used on the wings of aircraft, but also on wind turbines.

Safety first, even in air traffic. The effects of low temperatures this winter has been felt by almost every passenger. If the thermometer drops below zero degrees, previously frozen aircraft wings must first be defrosted with de-icing agent. Ice on the wings disturbs the aerodynamics the current necessary for the lift could break off.

Provision is also made during the flight. Part of the hot engine exhaust air is diverted and directed into the wings. These are thus heated, so to speak, to prevent re-freezing. Expensive and climate-friendly effect: The fuel consumption of the aircraft can increase by up to 30 percent.

Anti-ice equipment for plastic surfaces

Researchers at the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB are therefore developing together with partners in the project sponsored by the Federal Ministry of Education and Research (BMBF) and by the project sponsor Karlsruhe (PTKA). The joint project Nanodyn is an anti-icing equipment for plastic surfaces.

For this purpose, they produce water-repellent micro- and nanostructured layers, on which water remains liquid even at temperatures below zero and thus does not form any ice at all. The reason: The layers do not provide crystallization nuclei on the surface of the water that wants to freeze, and it remains in a "highly supercooled" English supercooled state. display

"And even if the water freezes, our anti-icing equipment reduces ice adherence by more than 90 percent, " confirms Michael Haupt of the IGB, the test results in the ice chamber at minus 30 degrees,

Highly reactive gas mole fractions

The researchers use plasma technologies to separate the structured layers onto plastic films made of impact and impact-resistant polyurethane (PU). For this purpose, the film is guided into a vacuum chamber in which a so-called plasma modifies the surface. In a plasma, gas molecules are excited and fragmented by applying a high-frequency electrical voltage.

HochThe highly reactive gas mole fractions can now be coupled to the surface of the films: a layer is formed, explains the main. "By optimizing various process parameters, such as the type and amount of plasma gas used, the temperature, the pressure and the treatment time, we can produce very thin nanostructured layers."

These ordered structures are only a few nanometers in size, but have a great influence on the wetting properties: If water is brought to the surface of the film, it contracts into a spherical droplet, which then only due to the minimal interaction with the surface of it is repelled.

Never de-air planes again?

And how is the film on the aircraft wings? We can transfer the developed process to the industrial scale. One of our project partners, a plant manufacturer, can coat roll-to-roll entire film webs in large plasma chambers, "says Haupt. And the nanostructured film could then simply be glued to the wings. The costly de-icing of aircraft, large quantities of de-icing agents, and above all aviation fuel, could be saved and thus significant amounts of CO2 emissions avoided.

The fields of application are varied: Even on wind turbines, which stop in winter due to icing or run unbalanced, on solar panels, overhead lines and building parts, nanostructured surfaces would serve well. In addition, anti-icing equipment would make a significant contribution to safety.

(Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB, 28.02.2011 - DLO)