Lotus effect: Difference between revisions
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Further applications have been marketed, such as self-cleaning glasses installed in the sensors of traffic control units on German autobahns developed by a cooperation partner (Ferro GmbH). Evonik AG has developed a spray for generating self-cleaning films on various substrata. |
Further applications have been marketed, such as self-cleaning glasses installed in the sensors of traffic control units on German autobahns developed by a cooperation partner (Ferro GmbH). Evonik AG has developed a spray for generating self-cleaning films on various substrata. |
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Lotus effect [[superhydrophobic]] coatings applied to microwave antennas can significantly reduce [[rain fade]] and the buildup of ice and snow. |
Lotus effect [[superhydrophobic]] coatings applied to microwave antennas can significantly reduce [[rain fade]] and the buildup of ice and snow. A UK company has patented an approach for generating aerosols for use in personal care and household products by firing a low pressure jet of water-based product at a disc of a superhydrophobic material. <ref> <nowiki> "42T revolutionises aerosol production process" </nowiki>. ''Business Weekly'', 3 Feb 2011. page 16. Also [http://www.businessweekly.co.uk/index.php?option=com_content&view=article&id=38000]. Checked 11 Feb 2011.</ref> |
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“Easy to clean” products in ads are often mistaken in the name of the self-cleaning process of the lotus-effect. Patterned superhydrophobic surfaces also have the promises for the lab-on-a-chip, microfluidic devices and can drastically improve the surface based bioanalysis.<ref name=Ressine2007>{{cite journal|author = Ressine, A.|coauthors = Marko-Varga, G., Laurell, T.|year = 2007|title = Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout|journal = Biotechnology Annual Review|volume = 13|pages = 149–200|doi = 10.1016/S1387-2656(07)13007-6|pmid = 17875477}}</ref> |
“Easy to clean” products in ads are often mistaken in the name of the self-cleaning process of the lotus-effect. Patterned superhydrophobic surfaces also have the promises for the lab-on-a-chip, microfluidic devices and can drastically improve the surface based bioanalysis.<ref name=Ressine2007>{{cite journal|author = Ressine, A.|coauthors = Marko-Varga, G., Laurell, T.|year = 2007|title = Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout|journal = Biotechnology Annual Review|volume = 13|pages = 149–200|doi = 10.1016/S1387-2656(07)13007-6|pmid = 17875477}}</ref> |
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Revision as of 15:32, 11 February 2011
 | It has been suggested that this article be merged with Superhydrophobe. (Discuss) Proposed since May 2009. |
The lotus effect refers to the very high water repellency (superhydrophobicity) exhibited by the leaves of the lotus flower (Nelumbo).[1] Dirt particles are picked up by water droplets due to a complex micro- and nanoscopic architecture of the surface, which minimizes adhesion.
This effect can easily be demonstrated in many other plants, for example tropaeolum, cane and columbine, and on the wings of certain insects.
The phenomenon was first studied by Dettre and Johnson in 1964 using rough hydrophobic surfaces. Their work developed a theoretical model based on experiments with glass beads coated with paraffin or PTFE telomer. The self-cleaning property of superhydrophobic micro-nanostructured surfaces was reported by Barthlott and Ehler in 1977,[2] and perfluoroalkyl and perfluoropolyether superhydrophobic materials were developed by Brown in 1986 for handling chemical and biological fluids.[3] Other biotechnical applications have emerged since the 1990s.[4][5][6][7][8]
Functional principle
Due to their high surface tension, water droplets tend to minimize their surface trying to achieve a spherical shape. On contact with a surface, adhesion forces result in wetting of the surface. Either complete or incomplete wetting may occur depending on the structure of the surface and the fluid tension of the droplet.[9] The cause of self-cleaning properties is the hydrophobic water-repellent double structure of the surface.[10] This enables the contact area and the adhesion force between surface and droplet to be significantly reduced resulting in a self-cleaning process.[11][12][13] This hierarchical double structure is formed out of a characteristic epidermis (its outermost layer called the cuticle) and the covering waxes. The epidermis of the lotus plant possesses papillae with 10 to 20 µm in height and 10 to 15 µm in width on which the so-called epicuticular waxes are imposed. These superimposed waxes are hydrophobic and form the second layer of the double structure.
The hydrophobicity of a surface is determined by the contact angle. The higher the contact angle the higher the hydrophobicity of a surface. Surfaces with a contact angle < 90° are referred to as hydrophilic and those with an angle >90° as hydrophobic. Some plants show contact angles up to 160° and are called super-hydrophobic meaning that only 2–3% of a drop's surface is in contact. Plants with a double structured surface like the lotus can reach a contact angle of 170° whereas a droplet’s actual contact area is only 0.6%. All this leads to a self-cleaning effect.
Dirt particles with an extremely reduced contact area are picked up by water droplets and are thus easily cleaned off the surface. If a water droplet rolls across such a contaminated surface the adhesion between the dirt particle, irrespective its chemistry, and the droplet is higher than between the particle and the surface. As this self-cleaning effect is based on the high surface tension of water it does not work with organic solvents. Therefore, the lotus-effect is no protection against graffiti.
This effect is of a great importance for plants as a protection against pathogens like fungi or algae growth, and also for animals like butterflies, dragonflies and other insects not able to cleanse all their body parts. Another positive effect of self-cleaning is the prevention of contamination of the area of a plant surface exposed to light resulting in a reduced photosynthesis.
Technical application
Some nanotechnologists have developed treatments, coatings, paints, roof tiles, fabrics and other surfaces that can stay dry and clean themselves in the same way as the lotus leaf. This can usually be achieved using special fluorochemical or silicone treatments on structured surfaces or with compositions containing micro-scale particulates. Super-hydrophobic coatings comprising Teflon microparticles have been used on medical diagnostic slides for over 30 years. It is possible to achieve such effects by using combinations of polyethylene glycol with glucose and sucrose (or any insoluble particulate) in conjunction with a hydrophobic substance.
As self cleaning of superhydrophobic microscopic to nanoscopic surfaces is based on a purely physio-chemical effect it can be transferred onto technical surfaces on a biomimetic basis.[14][15][16] The first and most successful product with superhydrophobic self-cleaning properties was the facade paint Lotusan launched in 1999, and it has been applied on more than 500,000 buildings worldwide so far.[17]
Further applications have been marketed, such as self-cleaning glasses installed in the sensors of traffic control units on German autobahns developed by a cooperation partner (Ferro GmbH). Evonik AG has developed a spray for generating self-cleaning films on various substrata. Lotus effect superhydrophobic coatings applied to microwave antennas can significantly reduce rain fade and the buildup of ice and snow. A UK company has patented an approach for generating aerosols for use in personal care and household products by firing a low pressure jet of water-based product at a disc of a superhydrophobic material. [18]
“Easy to clean” products in ads are often mistaken in the name of the self-cleaning process of the lotus-effect. Patterned superhydrophobic surfaces also have the promises for the lab-on-a-chip, microfluidic devices and can drastically improve the surface based bioanalysis.[19]
Research history
 | This section contains content that is written like an advertisement. (April 2010) |
Although the self-cleaning phenomenon of the lotus was known in Asia for more than 2000 years (reference to lotus effect found in Bhagavad Gita [20] padmapatramivambhasa), its mechanism was explained only in the early 1970s with introduction of the scanning electron microscope.[2][13] First trials were performed with Tropaeolum and first in-depth studies were conducted on Lotus leaves (Barthlott & Neinhuis, 1997). By the mid 1990s, Wilhelm Barthlott developed industrial products and trademarked the principle as Lotus-Effect.[21]
See also
References
- ^ Lafuma, A. (2003). "Superhydrophobic states". Nature Materials. 2 (7): 457–460. doi:10.1038/nmat924. PMID 12819775.
{{cite journal}}: Unknown parameter|coauthor=ignored (|author=suggested) (help) - ^ a b Barthlott, Wilhelm (1977). "Raster-Elektronenmikroskopie der Epidermis-Oberflächen von Spermatophyten". Tropische und subtropische Pflanzenwelt. 19. Akad. Wiss. Lit. Mainz: 110.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Brown Laboratory vessel having hydrophobic coating and process for manufacturing same U.S. patent 5,853,894, Issued December 29, 1998
- ^ Barthlott, Wilhelm (1997). "The purity of sacred lotus or escape from contamination in biological surfaces". Planta. 202: 1–8. doi:10.1007/s004250050096.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Cheng, Y. T., Rodak, D. E. (2005). "Is the lotus leaf superhydrophobic?". Appl. Phys. Lett. 86 (14): 144101. doi:10.1063/1.1895487.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Narhe, R. D., Beysens, D. A. (2006). "Water condensation on a super-hydrophobic spike surface". Europhys. Lett. 75 (1): 98–104. doi:10.1209/epl/i2006-10069-9.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Lai, S.C.S. "Mimicking nature: Physical basis and artificial synthesis of the Lotus effect" (PDF).
- ^ Koch, K. (2008). "Diversity of structure, Morphology and Wetting of Plant Surfaces. Soft matter". Soft Matter. 4: 1943. doi:10.1039/b804854a.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ von Baeyer, H. C. (2000). "The Lotus Effect". The Sciences. 40: 12–15.
- ^ Neinhuis, C. (1997). "Characterization and distribution of water-repellent, self-cleaning plant surfaces". Annals of Botany. 79: 667–677. doi:10.1006/anbo.1997.0400.
{{cite journal}}: Unknown parameter|coauthor=ignored (|author=suggested) (help) - ^ Barthlott, Wilhelm (2001). "The lotus-effect: nature's model for self cleaning surfaces". International Textile Bulletin. 1: 8–12.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Forbes, P. (2005). The Gecko’s Foot, Bio-inspiration – Engineering New Materials and devices from Nature. London: Fourth Estate. p. 272. ISBN 0-00-717990-1.
- ^ a b Forbes, P. (2008). "Self-Cleaning Materials". Scientific American. 299 (2): 67–75.
- ^ Solga, A. (2007). "The dream of staying clean: Lotus and biomimetic surfaces". Bioinspiration & Biomimetics. 2: 1–9.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Mueller, T. (April 2008). "Biomimetics, Design by Nature". National Geographic Magazine: 68.
- ^ Guo, Z. (2005). "Stable Biomimetic Super-Hydrophobic Engineering Materials". J. Am. Chem. Soc. 127 (45): 15670–15671. doi:10.1021/ja0547836. PMID 16277486.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ lotusanpage
- ^ "42T revolutionises aerosol production process" . Business Weekly, 3 Feb 2011. page 16. Also [1]. Checked 11 Feb 2011.
- ^ Ressine, A. (2007). "Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout". Biotechnology Annual Review. 13: 149–200. doi:10.1016/S1387-2656(07)13007-6. PMID 17875477.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Gita Verse 5–10
- ^ Also registered trademark No. 4790998 of Wilhelm Barthlott in Japan since 30 July 2004.
External links
