New silicone coating inhibits bio-fouling on ship hulls

A research team from the Zoological Institute of Kiel University (CAU) has succeeded in developing a new silicone coating with a specific microstructure which reduces the contact area of barnacles to ships hulls by more than 50 percent, and thus prevents the permanent attachment of them. First application tests on sailing yachts have been promising so far. The results of this study, which was supported by the Cluster of Excellence “The Future Ocean” in Kiel, were published on 22th of August in the renowned scientific Journal of The Royal Society Interface.

© Lars Heepe und Dennis Petersen.
3-dimensional visualization of the surfaces of the micro-structured silicone surface (left) and the smooth control surface made of the same silicone (right). The control surface is much more heavily overgrown with barnacles.

The development of functional surfaces inspired by nature has received a lot of attention in science and industry. Especially in maritime industries there is a great interest in innovative solutions to prevent the undesirable adhesion of mussels or barnacles to ship hulls or offshore facilities, so called bio-fouling.

Adhesion plays an important role in nature. Barnacles and mussels use complex adhesives to permanently settle on natural and man-made surfaces such as ship hulls or offshore facilities. In the long term, organisms can damage these surfaces and, for example, increase fuel consumption through greater flow resistance.

Searching for non-toxic alternatives

Conventional methods to protect ship hulls against unwanted bio-fouling are often associated with environmentally harmful toxins. The researchers were therefore looking for new ways to overcome the permanent growth of macro-fouling without toxic substances being introduced into the sea.

For the development of the new surface, the researchers first analysed the wettability of the barnacle cement, meaning the ability of the organisms to adhere to surfaces underwater and to spread their “cement” throughout the surface, then developed strategies to fight it by introducing an appropriate surface microstructure.

“Our research has shown that adhesives used by organisms that settle underwater can stick to almost any surface. The reason is the complex chemical composition of these adhesives. The aim of our research was therefore to develop a surface as universal as possible, which, based on physical principles, prevents the organisms from adhering permanently,” says first author Dennis Petersen from the Zoological Institute of Kiel University.

Microstructure with lotus effect

The result is a coating made of a non-toxic silicone with a new microstructure similar to that of a mushroom head, causing liquids to roll off smooth surfaces. The geometry of this new structure prevents a strong adhesive bond between barnacles or mussels with the newly developed coating surface.

In a first practical test, parts of the hull of four sailing yachts of the Kiel Yacht Club were covered with the new material and tested for one season. The tests have proven: No barnacles or other macro-foulers such as mussels could be found on the new coating.

“In addition to the technological relevance, our work also makes a fundamental contribution to the bio-mechanics of the adhesion of marine organisms. Underwater adhesion still remains a mystery to scientists. Only by comparing the overgrowth on different surfaces we are able to understand the process of adhesion of marine organisms. With this understanding, it will certainly be possible to develop further innovative strategies for a toxin-free reduction of bio-fouling,” said Prof. Dr. Stanislav Gorb, co-author of the study and member of the Cluster of Excellence “The Future Ocean”.

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