Superhydrophobic surfaces show ‘world-record effectiveness’

Researchers in China and Finland have developed armour-plated superhydrophobic surfaces that repel liquids with what is claimed to be ‘world-record effectiveness’.

Superhydrophobic surfaces
A schematic representation of how the surface looks, and how the structure repels water (Image: Aalto University)

Superhydrophobic surfaces are extremely useful for antimicrobial coatings because bacteria, viruses and other pathogens cannot hold on to their surfaces. Such surfaces are, however, susceptible to cuts, scratches or dents that can trap liquids and render the coatings ineffective.

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The research – featured in Nature – is said to have designed superhydrophobic surfaces that can be made from metal, glass, or ceramic. The superhydrophobic properties of the surface come from nano-sized structures spread over it. The surface of the material is patterned with a honeycomb-like structure of tiny inverted pyramids. The water-repellent chemical is then coated on the inside the honeycomb. This prevents any liquid from sticking to the surface, and the delicate chemical coating is protected from damage by the pyramid’s walls.

“The armour can be made from almost any material, it’s the interconnection of the surface frame that makes it strong and rigid,” said Professor Robin Ras, a physicist at Aalto University whose research group was part of the project. “We made the armour with honeycombs of different sizes, shapes and materials. The beauty of this result is that it is a generic concept that fits for many different materials, giving us the flexibility to design a wide range of durable waterproof surfaces.”

The superhydrophobic surfaces can also be used more generally in any application requiring a liquid-repellent surface, such as photovoltaics where the build-up of moisture and dirt over time blocks the amount of light they can absorb.

Making a solar panel out of a superhydrophobic glass surface would maintain their efficiencies over long periods of time. Furthermore, as solar cells are often on roof tops and other difficult to reach locations, the repellent coatings would cut down the amount of cleaning required.

“By using the decoupled design, we introduce a new approach for designing a robust superhydrophobic surface. Our future work would be to push this method further, and to transfer robust superhydrophobic surfaces to different materials and its commercialisation” said Professor Xu Deng, the leader of the group at the University of Electronic Science and Technology of China in Chengdu who took part in this research.

Other desirable applications for superhydrophobic surfaces include in machines and on vehicles, where conditions can be challenging for brittle materials over long periods of time. To simulate these working environments, the researchers are said to have subjected their new surfaces to extreme conditions, including baking them at 100°C non-stop for weeks, immersing them in highly corrosive liquids for hours, blasting them with high-pressure water jets, and subjecting them to physical exertion in extreme humidity. According the team, the surfaces were still able to repel liquid as effectively as before.

Now that the strengths of this new material design have been demonstrated, future research will explore its real-world applications.