28:
137:. 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 ultrahydrophobic, meaning that only 2–3% of the surface of a droplet (of typical size) is in contact. Plants with a double structured surface like the lotus can reach a contact angle of 170°, whereby the droplet's contact area is only 0.6%. All this leads to a self-cleaning effect.
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force between surface and droplet to be significantly reduced, resulting in a self-cleaning process. 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 10 ÎĽm to 20 ÎĽm in height and 10 ÎĽm to 15 ÎĽm in width on which the so-called
44:
210:" respectively. In October 2005, tests of the Hohenstein Research Institute showed that clothes treated with NanoSphere technology allowed tomato sauce, coffee and red wine to be easily washed away even after a few washes. Another possible application is thus with self-cleaning awnings, tarpaulins and sails, which otherwise quickly become dirty and difficult to clean.
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the particle and the surface. This cleaning effect has been demonstrated on common materials such as stainless steel when a superhydrophobic surface is produced. As this self-cleaning effect is based on the high surface tension of water it does not work with organic solvents. Therefore, the hydrophobicity of a surface is no protection against graffiti.
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When it was discovered that the self-cleaning qualities of ultrahydrophobic surfaces come from physical-chemical properties at the microscopic to nanoscopic scale rather than from the specific chemical properties of the leaf surface, the possibility arose of using this effect in manmade surfaces, by
140:
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 of its chemistry, and the droplet is higher than between
110:
and Ehler in 1977, who described such self-cleaning and ultrahydrophobic properties for the first time as the "lotus effect"; perfluoroalkyl and perfluoropolyether ultrahydrophobic materials were developed by Brown in 1986 for handling chemical and biological fluids. Other biotechnical applications
189:
In addition to chemical surface treatments, which can be removed over time, metals have been sculpted with femtosecond pulse lasers to produce the lotus effect. The materials are uniformly black at any angle, which combined with the self-cleaning properties might produce very low maintenance solar
124:
of the surface. Either complete or incomplete wetting may occur depending on the structure of the surface and the fluid tension of the droplet. The cause of self-cleaning properties is the hydrophobic water-repellent double structure of the surface. This enables the contact area and the adhesion
185:
and other surfaces that can stay dry and clean themselves by replicating in a technical manner the self-cleaning properties of plants, such as the lotus plant. This can usually be achieved using special fluorochemical or silicone treatments on structured surfaces or with compositions containing
217:
and the buildup of ice and snow. "Easy to clean" products in ads are often mistaken in the name of the self-cleaning properties of hydrophobic or ultrahydrophobic surfaces. Patterned ultrahydrophobic surfaces also show promise for "lab-on-a-chip" microfluidic devices and can greatly improve
410:
73:, the lotus flower. Dirt particles are picked up by water droplets due to the micro- and nanoscopic architecture on the surface, which minimizes the droplet's adhesion to that surface. Ultrahydrophobicity and self-cleaning properties are also found in other plants, such as
119:
The high surface tension of water causes droplets to assume a nearly spherical shape, since a sphere has minimal surface area, and this shape therefore minimizes the solid-liquid surface energy. On contact of liquid with a surface, adhesion forces result in
407:
343:
Barthlott, W. (2023): “The
Discovery of the Lotus Effect as a Key Innovation for Biomimetic Technologies” - in: Handbook of Self-Cleaning Surfaces and Materials: From Fundamentals to Applications, Chapter 15, pp. 359-369 - Wiley-VCH,
129:
are imposed. These superimposed waxes are hydrophobic and form the second layer of the double structure. This system regenerates. This biochemical property is responsible for the functioning of the water repellency of the surface.
94:
The phenomenon of ultrahydrophobicity 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
253:). Similar to lotus effect, a recent study has revealed honeycomb-like micro-structures on the taro leaf, which makes the leaf superhydrophobic. The measured contact angle on this leaf in this study is around 148 degrees.
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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 reduced photosynthesis.
193:
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). The Swiss companies
225:
has a lid with a microscopic pyramidal structure based on the ultrahydrophobic properties that funnel condensation and rainwater into a basin for release to a growing plant's roots.
691:
783:
Serles, Peter; Nikumb, Suwas; Bordatchev, Evgueni (2018-06-15). "Superhydrophobic and superhydrophilic functionalized surfaces by picosecond laser texturing".
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Superhydrophobic or hydrophobic properties have been used in dew harvesting, or the funneling of water to a basin for use in irrigation. The
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thermal energy collectors, while the high durability of the metals could be used for self-cleaning latrines to reduce disease transmission.
233:
Although the self-cleaning phenomenon of the lotus was possibly known in Asia long before (reference to the lotus effect is found in the
826:
Solga, A.; Cerman, Z.; Striffler, B. F.; Spaeth, M.; Barthlott, W. (2007). "The dream of staying clean: Lotus and biomimetic surfaces".
471:
Barthlott, W., Mail, M., Bhushan, B., & K. Koch. (2017). Plant
Surfaces: Structures and Functions for Biomimetic Innovations.
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Koch, K.; Bhushan, B.; Barthlott, W. (2008). "Diversity of structure, Morphology and
Wetting of Plant Surfaces. Soft matter".
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Rulon E. JohnsonJr.; Robert H. Dettre (1964). "Contact Angle
Hysteresis. III. Study of an Idealized Heterogeneous Surface".
435:
Barthlott, Wilhelm; C. Neinhuis (1997). "The purity of sacred lotus or escape from contamination in biological surfaces".
566:
388:
Barthlott, Wilhelm; Ehler, N. (1977). "Raster-Elektronenmikroskopie der
Epidermis-Oberflächen von Spermatophyten".
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Porous silicon protein microarray technology and ultra-/superhydrophobic states for improved bioanalytical readout
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883:
240:
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Guo, Z.; Zhou, F.; Hao, J.; Liu, W. (2005). "Stable
Biomimetic Super-Hydrophobic Engineering Materials".
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Barthlott, Wilhelm; Neinhuis, C. (2001). "The lotus-effect: nature's model for self cleaning surfaces".
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Narhe, R. D.; Beysens, D. A. (2006). "Water condensation on a super-hydrophobic spike surface".
27:
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1071:"Wetting characteristics of Colocasia esculenta (Taro) leaf and a bioinspired surface thereof"
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The Gecko's Foot, Bio-inspiration – Engineering New
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239:), its mechanism was explained only in the early 1970s after the introduction of the
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Superhydrophobic coatings applied to microwave antennas can significantly reduce
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567:"Mimicking nature: Physical basis and artificial synthesis of the Lotus effect"
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Laboratory vessel having hydrophobic coating and process for manufacturing same
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A water drop on a lotus surface showing contact angles of approximately 147°.
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leaf with lotus effect (upper), and taro leaf surface magnified (0–1 is one
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Video showing comparison between plant leaves with and without lotus effect
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979:"Lasers help create water-repelling, light-absorbing, self-cleaning metals"
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Cheng, Y. T.; Rodak, D. E. (2005). "Is the lotus leaf superhydrophobic?".
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This effect is of a great importance for plants as a protection against
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Project Group lotus effect - Nees
Institut for biodiversity of plants
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1000:. Biotechnology Annual Review. Vol. 13. pp. 149–200.
940:"Multifunctional surfaces produced by femtosecond laser pulses"
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have developed stain-resistant textiles under the brand names "
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mimicking nature in a general way rather than a specific one.
1166:"Self-Cleaning Materials: Lotus Leaf-Inspired Nanotechnology"
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Mueller, T. (April 2008). "Biomimetics, Design by Nature".
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Lafuma, A.; Quere, D. (2003). "Superhydrophobic states".
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have developed treatments, coatings, paints, roof tiles,
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refers to self-cleaning properties that are a result of
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The hydrophobicity of a surface can be measured by its
102:. The self-cleaning property of ultrahydrophobic micro-
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span) showing a number of small protrusions (lower).
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1038:"The different forms of condensation - Technology"
996:Ressine, A.; Marko-Varga, G.; Laurell, T. (2007).
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91:, cane, and also on the wings of certain insects.
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738:Forbes, P. (2008). "Self-Cleaning Materials".
625:von Baeyer; H. C. (2000). "The Lotus Effect".
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714:. London: Fourth Estate. p. 272.
23:Water on the surface of a lotus leaf.
1155:Friedrich-Wilhelm University of Bonn
654:Neinhuis, C.; Barthlott, W. (1997).
977:Borghino, Dario (21 January 2015).
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186:micro-scale particulates.
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1075:Scientific Reports
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1115:.
1093::
1085::
1040:.
1026:.
1004::
985:.
966:.
962::
954::
923:.
911::
870:.
858::
840::
834:2
815:.
803::
795::
772:.
760::
752::
724:.
697:1
678:.
672::
643:.
639::
614:.
610::
602::
596:4
554:.
550::
542::
518:.
514::
506::
483:.
477:9
461:.
449::
374:.
370::
333:.
313::
305::
299:2
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