Surfaces modeled on shark scales: microstructured coating protects against limescale
Researchers at ETH Zurich have developed a surface coating to which limescale does not adhere to prevent the formation of a closed layer of limescale.
A research team from ETH Zurich and the University of Berkeley has found a possible solution to calcification: a special lime-repellent coating that has microscopically small ribs and prevents the adhesion of lime crystals.
As there has been little basic knowledge on the development of limescale-repellent surfaces to date, the researchers led by former ETH professor Thomas Schutzius have investigated in detail how individual growing limescale crystals interact with the surrounding water flow and the surface on a microscopic level. Based on this, Schutzius’ doctoral student Julian Schmid and other team colleagues developed several coatings from various soft materials and tested them in the laboratory at ETH Zurich.
Ribbed surface does not hold limescale
The most effective coating turned out to be a polymer hydrogel, the surface of which the researchers provided with microscopically small ribs using photolithography. The microstructure of the hydrogel is reminiscent of that of natural models such as shark scales, which also have a ribbed structure, which suppresses the formation of surface deposits in sharks.
The ribs ensure that the lime crystals have less contact with the surface, cannot adhere and can therefore be removed more easily. Water flowing over the hydrogel and through the ribbed structure carries them away. The coating cannot prevent some limescale crystals from forming. However, the constant passive removal of the microscopic crystals prevents the crystals from coalescing into a stubborn layer.
Hardly any crystals stick
The researchers primarily varied the polymer content in the different coatings. The lower this is and the higher the water content, the less well the calcium carbonate crystals adhere to the surface.
Tests with model particles made of polystyrene show that the surface structures of the coating must be smaller than the particles that are deposited on it. This reduces the contact area and therefore the adhesion force. “We varied the surface structure of the material to achieve the greatest efficiency and carried out the crystal experiments with this optimum structure size,” says Schmid.
The experiments show that the hydrogel coating is very effective: up to 98 percent of all limescale crystals with a size of around ten micrometers that had previously grown on a hydrogel-coated surface were removed.
Advantage over chemical descaling
The researchers emphasize that their solution is more environmentally friendly and efficient than previous approaches to descaling. To date, toxic and aggressive chemicals have sometimes been used for this purpose. The hydrogel, on the other hand, is biocompatible and environmentally friendly. The technology would also be scalable. The coating could be applied in various ways that are already used in industry today.
The researchers have not yet filed a patent for their development, but have deliberately opted for publication in a scientific journal. This means that all interested parties are free to further develop the new coating and make it usable.
This research was published in Science Advances, Volume 9, Issue 51, 20 Dec 2023.
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