Technical coatings, on which water rolls off in large droplets so that the surfaces can clean themselves, have their model in nature. The best-known example is the leaves of the lotus plant. Artificial attempts have been made for years to imitate the lotus effect named after it.
This results in so-called superhydrophobic coatings, which can be used in many niche markets in the aerospace, marine, construction, automotive and biomedical industries. Of the various approaches, molding and creating imitations of the original surface (replicas) has proven to be the simplest method.
However, the microscopically fine structures in combination with the surface chemistry of the leaves cause problems here. In addition, the molding process either fails to reproduce the microscopic structures or to form replicas.
In an international research project, the working group led by Guido Kickelbick, Professor of Inorganic Solid State Chemistry at Saarland University, together with colleagues from Portugal and Sweden, has now succeeded in using special polymer combinations to precisely reproduce the surfaces of carob tree leaves.
As the surface of the leaves is coated with a type of wax that melts at low temperatures, it was not possible to use molten polymer for molding. Instead, special silicones were used that harden at low temperatures. The molded structures had to be reproduced in replicas without affecting the existing microscopic texture of the carob tree leaves. The team was able to achieve this by precisely coordinating the adhesion properties as well as the mechanical and other properties of the materials used. First, a highly flowable silicone is applied to the leaves. This wets the finest structures on the leaf surface. Once the silicone has hardened, it can be removed from the blade surface.
Original publication: Langmuir 2021, 37, 6, 2011-2028
DOI: 10.1021/acs.langmuir.0c02806
