The lotus effect ( protected as a brand name in the notation lotus effect ) is the low wettability of a surface, as can be seen in the lotus plant . Water rolls off in droplets and takes all dirt particles on the surface with it. This is due to the complex microscopic and nanoscopic architecture of the surface, which minimizes the adhesion of dirt particles.
Other plants, such as the nasturtium ( Tropaeolum ) , reed ( Phragmites ) , cabbage ( Brassica oleracea ) or the columbine ( Aquilegia ) , as well as some animals (many insect wings) , show this effect.
The self - cleaning ability of water - repellent micro-nanostructured surfaces was discovered in the 1970s and transferred to bionic products since the mid-1990s. These are identified by the industry with the brand name "Lotus Effect".
Due to their high surface tension, water droplets tend to minimize their surface area and therefore try to achieve a spherical shape. Upon contact with another surface act adhesion forces (adhesion forces to the surface), so that it for wetting the same comes. Depending on the nature of the surface and the surface tension of the liquid, complete (spreader) or incomplete wetting can occur.
The cause of the self-cleaning lies in a hydrophobic (water-repellent) double structure of the surface. This reduces the contact area and thus the adhesive force between the surface and the particles and water droplets lying on it so much that self-cleaning occurs. This double structure is formed from a characteristically shaped epidermis , the outermost layer of which is called the cuticle , and waxes on it. The epidermis of the lotus plant forms papillae about 10 to 20 micrometers high and 10 to 15 micrometers apart , on which the so-called epicuticular waxes are deposited. These are renewable substances. These deposited waxes are hydrophobic and form the second part of the double structure. This means that water no longer has the opportunity to get into the spaces between the leaf surface, with the result that the contact area between the water and the surface is drastically reduced.
The hydrophobicity of surfaces is determined by the contact angle . The higher the contact angle, the more hydrophobic the surface. Surfaces with a contact angle <90 ° are called hydrophilic, those with a contact angle> 90 ° are called hydrophobic. With some plants, contact angles of up to 160 ° ( superhydrophobicity ) can be achieved. This means that only about 2 to 3% of the droplet surface is in contact with the surface of the plant, which means that it has extremely low wettability . Due to the double structure of the lotus plant, its leaves can reach a contact angle of around 170 °, which means that a drop has a contact area of only around 0.6%. The adhesion between the leaf surface and the water droplets is so low that the water can easily roll off. Overlying dirt particles - which also only have a small contact area - are carried along and washed away. Even hydrophobic dirt particles are washed off the plant surface because their adhesion to the plant surface is less than to the water droplet.
Due to the central importance of the surface tension of aqueous solutions for minimizing the contact area, it is understandable that self-cleaning in this form cannot occur with strongly wetting solvents , which is why such surfaces do not provide any protection against any kind of paint or inks.
The biological significance of the lotus effect for the plant lies in the protection against colonization by microorganisms (e.g. pathogens ), against fungal spores or against growth with algae . Another positive effect of the self-cleaning is the prevention of pollution that the incidence of light and thus the photosynthesis reduce and stomata could close. The same applies to animals such as butterflies, dragonflies and other insects: their legs cannot reach every part of their body for cleaning; It is all the more advantageous when moisture and dirt roll off independently.
The technical and economic importance of self-cleaning surfaces is increasing. This coveted property through micro- and nano-structuring of superhydrophobic surfaces is a purely physical-chemical phenomenon and it can be transferred bionically to technical surfaces. There are now around 600,000 buildings with this product alone that are equipped with lotus effect surfaces.
The self-cleaning ability of water-repellent nanostructured surfaces was discovered in the 1970s by Wilhelm Barthlott . With regard to the technical teaching for the implementation of the self-cleaning effect, Barthlott applied for international patent protection. Furthermore, products that go back to the technical teaching developed by Barthlott for the implementation of the self-cleaning effect are comprehensively protected internationally by the brands "Lotus-Effekt" and "Lotus-Effect". The exclusive brand owner is Sto AG in Stühlingen, manufacturer, among other things, of the facade paints "Lotusan", which Sto AG launched in 1999 as the first commercial product in implementation of Barthlott's teaching.
Further areas of application are self-cleaning glasses based on the principle of the lotus plant from Ferro GmbH, which are used, for example, on Toll Collect cameras. The company Degussa AG has developed prototypes of plastics and sprays.
In advertising, so-called “easy-to-clean” surfaces are sometimes deliberately confused with self-cleaning surfaces based on the lotus principle.
The Swiss companies HeiQ Materials AG and Schoeller Textil AG have developed dirt-repellent textiles under the brand names "HeiQ Eco Dry" and "NanoSphere". In October 2005, tests by the Hohenstein Research Institute showed that clothes from the NanoSphere range allow tomato sauce, coffee and red wine to drain off even after being washed several times. There is another possible use for self-cleaning awnings, tarpaulins and sails, which otherwise get dirty quickly and are difficult to clean.
Although the phenomenon of the self-cleaning of lotus has been known in Asia for at least 2000 years (lotus is, among other things, the symbol of purity in Buddhism ), the effect was only investigated by the botanist Wilhelm Barthlott since the early 1970s with the use of scanning electron microscopy . The original work was mainly carried out on the nasturtium. The first scientifically fundamental analysis was carried out on the lotus leaves (W. Barthlott, C. Neinhuis). In the mid-1990s, these two authors also succeeded in the first implementation on technical prototypes and the first industrial collaborations. The processes are patented. Since the late 1990s, physicists and materials scientists in particular have studied the phenomenon intensively, and there is now a very extensive literature and dozens of dependent patents. Wilhelm Barthlott's work has been awarded numerous prizes for clarifying the functional principle of the self-cleaning surfaces of the lotus flower and its implementation in technical products (1997 Karl Heinz Beckurts Prize, 1998 nomination for the German Future Prize of the Federal President, 1999 Philip Morris Research Prize, 1999 German Environment Prize, 2005 Innovation Prize from the Federal Ministry of Education and Research and others).
- Z. Cerman, W. Barthlott, J. Nieder: Inventions of nature. Bionics - What we can learn from plants and animals . 3. Edition. Rowohlt Paperback, 2011, ISBN 978-3-499-62024-9 .
- P. Forbes: The Gecko's Foot: Bio-inspiration: Engineering New Materials from Nature . WW Norton, 2006, ISBN 0-393-06223-6 .
- Journal articles
- W. Barthlott: Scanning electron microscopy of the epidermal surface in plants . In: Scanning electron microscopy in taxonomy and functional morphology (= Systematics Association's Special ). tape 41 , 1990, pp. 69-94 .
- W. Barthlott, W. Erdelen, M. Daud Rafiqpoor: Biodiversity and technical innovations: bionics . In: Concept and Value in Biodiversity. Routledge Studies in Biodiversity Politics and Management . 2014, ISBN 978-0-415-66057-0 , pp. 300-315 .
- W. Barthlott, T. Schimmel et al. a .: The Salvinia paradox: Superhydrophobic surfaces with hydrophilic pins for air retention under water . In: Advanced Materials . tape 22 , 2010, p. 2325–2328 , doi : 10.1002 / adma.200904411 .
- P. Forbes: Self-Cleaning Materials . In: Scientific American Magazine . tape 299 , no. 2 , 2008, p. 88-95 , doi : 10.1038 / scientificamerican0808-88 .
- S. Herminghaus: Roughness-induced non-wetting . In: Europhysics Letters . tape 52 , no. 2 , 2000, pp. 165–170 , doi : 10.1209 / epl / i2000-00418-8 .
- K. Koch, B. Bhushan, W. Barthlott: Diversity of structure, morphology and wetting of plant surfaces . In: Soft Matter . tape 4 , no. 10 , 2008, p. 1943-1963 , doi : 10.1039 / b804854a .
- A. Lafuma, D. Quéré: Superhydrophobic states . In: Nat Mater . tape 2 , no. 7 , 2003, p. 457-460 , doi : 10.1038 / nmat924 .
- Andreas Solga, Zdenek Cerman, Boris F. Striffler, Manuel Spaeth, Wilhelm Barthlott: The dream of staying clean: Lotus and biomimetic surfaces . In: Bioinspiration & Biomimetics . tape 2 , no. 4 , 2007, p. S126-S134 , doi : 10.1088 / 1748-3182 / 2/4 / S02 .
- HC von Baeyer: The lotus effect . In: The Sciences . tape 40 , 2000, pp. 95-106 .
- T. Wagner, C. Neinhuis, W. Barthlott: Wettability and contaminability of insect wings as a function of their surface sculptures . In: Acta Zoologica . tape 77 , 1996, pp. 213-225 , doi : 10.1111 / j.1463-6395.1996.tb01265.x .
- YY Yan, N. Gao, W. Barthlott: Mimicking natural superhydrophobic surfaces and grasping the wetting process: A review on recent progress in preparing superhydrophobic surfaces . In: Advances in Colloid and Interface Science . tape 169 , 2011, pp. 80-105 , doi : 10.1016 / j.cis.2011.08.005 .
- Page of the discoverer of self-cleaning, Prof. Dr. Wilhelm Barthlott www.lotus-salvinia.de
- Cassie's law in the English language Wikipedia - A work from 1944 on the subject
- ↑ Information on the Lotus-Effekt trademark in the register of the German Patent and Trademark Office (DPMA)
- ↑ Rolf Froböse: When frogs fall from the sky. The craziest natural phenomena . Wiley-VCH, Weinheim 2007, ISBN 3-527-31659-0 , pp. 170 .
- ↑ Lotusan
- ↑ HeiQ Eco Dry | HeiQ Materials AG. (No longer available online.) In: heiq.com. Archived from the original on August 12, 2016 ; accessed on August 24, 2016 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Textile coatings: Nanotechnology turns fabrics into high-tech fabrics. Archived from the original on April 7, 2014. Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: The screen printing . March 2009. Retrieved December 4, 2010.
- ↑ W. Barthlott, N. Ehler: Scanning Electron Microscopy of the Epidermis Surfaces of Spermatophytes . In: Tropical and subtropical flora . tape 19 , 1977, pp. 367-467 .
- ↑ W. Barthlott, E. Wollenweber: On fine structure, chemistry and taxonomic significance of epicuticular waxes and similar secretions . In: Tropical and subtropical flora . tape 32 , no. 1 , 1981, p. 35-97 .
- ↑ W. Barthlott, C. Neinhuis: Purity of the sacred lotus, or escape from contamination in biological surfaces . In: Planta . tape 202 , no. 1 , 1997, p. 1-8 , doi : 10.1007 / s004250050096 .
- ↑ C. Neinhuis, W. Barthlott: Characterization and Distribution of Water-repellent, Self-cleaning Plant Surfaces . In: Ann. Bot. Band 79 , no. 6 , 1997, pp. 667-677 ( oxfordjournals.org [accessed November 2, 2008]).