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Sustainability / Natural Coatings
A research team from ETH Zurich and the University of California, Berkeley find a possible solution to limescale formation. It is a special limescale-repellent coating with microscopically small ridges. The ridges prevent the adhesion of limescale crystals.
Coating Surface with Tiny Ridges
Fundamental research into the development of limescale-repellent surfaces has been sparse. The researchers took a close look at the interactions among individual growing limescale crystals. They also studied the surrounding water flow and the surface at the microscopic level.
Based on this, Julian Schmid and other team members developed several coatings from various soft materials. They tested them in the lab at ETH Zurich. The research team is led by former ETH professor Thomas Schutzius. And Julian Schmid is Schutzius’ doctoral student.
The most effective coating turned out to be a polymer hydrogel. The coating surface is covered in tiny ridges due to microtextured molds. The researchers fabricated it using photolithography. The hydrogel’s microstructure is reminiscent of natural models such as shark scales. Shark scales also have a ribbed structure to suppress fouling on the sharks’ skin.
In kettles or boilers, the riblets ensure that the limescale crystals have less contact with the surface. This means they can’t adhere and are thus easier to remove. The water flowing over the hydrogel and through the ribbed structure carries them away.
The coating can’t fully prevent limescale crystals from forming. But the constant passive removal of the microscopic crystals stops them growing together to form a tenacious layer.
Biocompatible & Environmentally Friendly Solution
In producing the different coatings, the researchers primarily varied the polymer content. Lower polymer content and higher water content leads to less adhesion of calcium carbonate crystals to the surface.
Tests were carried out using model particles made of polystyrene. The test shows that the coating’s surface structures must be smaller than the particles that are deposited on it. This reduces the contact surface and thus the adhesive force. “
We varied the material’s surface structure to achieve the greatest efficiency. Then carried out the crystal experiments with this optimum structure size,” said Schmid.
The team’s experiments show that the hydrogel coating is very effective. The experiment was carried out on a hydrogel-coated surface. Previously, limescale crystals with a size of around 10 micrometers had been grown. But when water flowed across the hydrogel-coated surface, up to 98 percent of the crystals were removed.
The researchers emphasize that their solution is more eco-friendly. It is also more efficient than existing approaches to descaling. Some even involve toxic and aggressive chemicals. In contrast, hydrogel is biocompatible and environmentally friendly.
The technology behind this solution should also be scalable. The coating could be applied in various ways that are already in use in industry today. The researchers have deliberately decided in favor of publication in a scientific journal. This means that all interested parties are free to further develop and utilize the new coating.
View complete paper at: https://www.science.org/doi/10.1126/sciadv.adj0324
Source: Eidgenössische Technische Hochschule Zürich