How the lotus effect revolutionizes facades and roofs
The lotus effect is a well-known prime example of bionics, which deals with the creative transfer of natural phenomena into technology. Nature is used as a model and inspiration for ideas, innovative products, processes and problem solutions. The further development of nanotechnology has opened up new applications for bionics in the industrial innovation process in the building materials industry.
The lotus effect principle
In concrete terms, the "lotus effect" is the ability of a surface to clean itself of dirt. This property was discovered in the 1970s by the German botanist Prof. Dr. Wilhelm Barthlott of the University of Bonn in the lotus plant, which grows in muddy waters but whose leaves are always perfectly clean.
Barthlott realized that lotus leaves are not smooth as previously thought, but are covered with a multitude of tiny pimples made of water-repellent wax crystals. Dirt, fungal spores, bacteria and algae remain on the microscopically small pimples and are washed off with the next downpour.
The discovery of the lotus effect led to a paradigm shift in certain areas of materials science and enabled the development of superhydrophobic (water-repellent) bionic surfaces. The building materials industry in particular has taken advantage of nature's self-cleaning powers.
The lotus effect in the building materials industry
As long as the lotus effect is known, it took so long to be picked up and finally commercialized. The first commercial product with a self-cleaning effect was not launched on the market until the late 1990s with the facade paints "Lotusan" from Sto AG. Due to the further development of nanotechnology, numerous other technical applications of the lotus effect came onto the building materials market in the following years:
- Self-cleaning glass facades, solar modules and windows
- Self-cleaning nano-based facade coatings and plasters
- Self-cleaning roof tiles
- Nano-sealing in sanitary areas (shower glass wall, tiles, etc.)
Nano-sealers use the pearl-off effect of lotus blossom. They contain nanoparticles with components that bond firmly during surface sealing. The surface remains water-repellent, but can get so wet that the dirt is removed with water.
Longer service life for glass facades and windows
Dirty glass facades not only entail high cleaning costs, they also reduce light transmission and have an unfavourable effect on the daylight quotients in the interior. The degree of soiling of a glass façade is therefore considered a significant reduction factor in the design of daylight incidence.
The development of self-cleaning glass based on the lotus effect has significantly reduced this problem and at the same time minimized glass corrosion and the costs of cleaning the façade. An invisible special layer on the outside of the glass pane ensures that no dirt adheres to the surface. Due to the water-repellent surface, the rainwater rolls off and takes the existing dirt particles with it.
In most cases, sealing today is based on the photocatalytic effect of titanium dioxide. The coating is permanently burnt into the glass. Currently, products for the subsequent sealing of glass and other surfaces are also available on the market. However, the service life of such coatings is limited.
Lotus effect also with solar control glass
The self-cleaning effect can also be achieved with a solar control glass. For this purpose, the outer pane of the insulating glass is coated with a sun protection film which has the lotus effect and at the same time shields up to 80 percent of the sun's rays. Self-cleaning glass with solar protection film is used for glass facades, roof glazing, canopies or glass surfaces that are difficult to access. A prominent example of this is the Unilever headquarters in Hamburg's Hafencity. ETFE foils with lotus effect were used for the façade so as not to impair the view to the outside.
Self-cleaning coating for solar modules
Contaminated solar modules reduce the yield by up to 20 percent. A solution to this problem was found by coating the solar modules with titanium dioxide. Under the influence of light, titanium dioxide releases reactive oxygen from the ambient air, which reliably decomposes all organic deposits by oxidation ("cold combustion"). The remaining impurities are then washed off by dew and rain.
The roof that cleans itself
Self-cleaning roof tiles are based on the same principle. In order to protect the roof from algae, soot and moss formation, nano coatings with a lotus effect are also most effective here. Both baked-in surface seals based on photocatalysis and subsequent finishing are offered as variants. As in the case of glass facades and windows, the latter have a shorter service life.
Facade paint with lotus effect
A facade paint or plaster cannot reproduce new wax crystals like a lotus leaf, but a self-cleaning facade - like all facades - shows a crumbling of very fine particles. This very slow chalking always causes newly exposed micro-surfaces, which show an intact lotus structure. The facade paint regenerates itself. Concrete and plaster facades can be made water-repellent in this way and protect the surface from deposits, cracks or lime and concrete efflorescence. High renovation costs for these facades can be reduced.
Graffiti protection with nanocoating
Graffiti protection is a recurring theme in some areas. Above all in large cities or in socially deprived areas, damage runs into the millions every year. Although graffiti removal agents already exist that achieve good results on smooth surfaces or glass facades, cleaning mineral materials such as stone, plaster, concrete or clinker is usually much more complex.
Nanocoatings that take advantage of the lotus effect offer less surface for graffiti to attack. They have the advantage that no veil remains on the façade after cleaning and therefore no new façade coating is required. Graffiti on a facade with a nanocoating should be removed up to ten times without leaving any residue.
Conclusion: lotus effect in the building materials industry
The use of nanotechnology has made the lotus effect usable for the building materials industry. Glass, ceramics, plaster, concrete, paints, solar modules and even roof tiles can already clean themselves today. However, those who expect a 100 percent cleaning will be disappointed. This means that even glass facades with a lotus effect will have to be cleaned at certain points and self-cleaning facade bases will always show a low level of impurities. Nevertheless, we can look forward to innovative bionic building materials in the future.
Born and raised in Vienna. Since 2012 she has been in charge of Business Development at LEAD Innovation with the functions marketing, sales and communication.