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Surface allows self-cleaning: sacred lotus

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The hydrophobic nature of the lotus leaf enables it to keep clean of dirt. / ForestMind / LicenseCC-by-nc-sa - Attribution Non-commercial Share Alike

Leaves of the sacred lotus are self-cleaning thanks to hydrophobic microscale bumps.

Lotus plants (Nelumbo nucifera) stay dirt-free, an obvious advantage for an aquatic plant living in typically muddy habitats, and they do so without using detergent or expending energy. The plant's cuticle, like that of other plants, is made up of soluble lipids embedded in a polyester matrix – wax – but the degree of its water repellency is extreme (superhydrophobic). This is accomplished through the micro-topography of their leaf surfaces, which while showing a variety of structures, all share a similar mathematical set of proportions associated with superhydrophobicity.

Lotus leaves, for example, exhibit extensive folding (i.e., papillose epidermal cells) and epicuticular wax crystals jutting out from the plant's surface, resulting in a roughened microscale surface. As water and air adhere less well than water and solids, roughened surfaces tend to reduce adhesive force on water droplets, as trapped air in the interstitial spaces of the roughened surface result in a reduced liquid-to-solid contact area. This allows the self-attraction of the polar molecule of water to express more fully, causing it to form spheres. Dirt particles on the leaf's surface stick to these droplets, both due to natural adhesion between water and solids and because contact with the leaf surface is reduced by over 95% from the leaf's micro-topography. The slightest angle in the surface of the leaf (e.g., caused by a passing breeze) then causes the balls of water to roll off due to gravity, taking the attached dirt particles with them and cleaning the leaf without using detergent or expending energy.

Surface finishes inspired by the self-cleaning mechanism of lotus plants and other organisms (e.g., many large-winged insects) have now been applied to paints, glass, textiles, and more, reducing the need for chemical detergents and costly labor.

This summary was contributed by Ashley Meyers.

This video gives you a closer look at the surface of the lotus leaf.

Learn more about the lotus' strategy in Tom McKeag's case study, "Return of the Swamp Thing" on pages 12-15 of Zygote Quarterly:
"The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data...it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the 'Lotus-Effect' and which may be of great biological and technological importance." (Barthlott and Neinhuis 1997:1)
About the inspiring organism
Med_1332550041_7991b551e8_b Sacred lotus
Nelumbo nucifera Gaertn.

Habitat(s): Wetlands
Learn more at EOL.org
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

IUCN Red List Status: Unknown

Bioinspired products and application ideas

Application Ideas: Self-cleaning, water-repellent surfaces

Industrial Sector(s) interested in this strategy: Buildings, manufacturing, automobiles, kitchen and bath, textiles

Wilhelm Barthlott Christoph Neinhuis (Institut fĂĽr Botanik) Holger F. Bohn
Nees-Institut für Biodiversität der Pflanzen
Barthlott, W.; Neinhuis, C. 1997. Purity of the sacred lotus, or escape from contamination in biological surfaces. Planta. 202(1): 1-8.
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Neinhuis, C.; Barthlott, W. 1997. Characterization and distribution of water-repellent, self-cleaning plant surfaces. Annals of Botany. 79(6): 667-677.
Learn More at Google Scholar Google Scholar  

Nature's Raincoats. Nottingham Trent University, University of Oxford.
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"If you scale this up, you could potentially catch an oil spill with a net," said Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of mechanical engineering at Ohio State.

The work was partly inspired by lotus leaves, whose bumpy surfaces naturally repel water but not oil. To create a coating that did the opposite, Bhushan and postdoctoral researcher Philip Brown chose to cover a bumpy surface with a polymer embedded with molecules of surfactant—the stuff that gives cleaning power to soap and detergent. They sprayed a fine dusting of silica nanoparticles onto the stainless steel mesh to create a randomly bumpy surface and layered the polymer and surfactant on top. The silica, surfactant, polymer, and stainless steel are all non-toxic and relatively inexpensive, said Brown. He estimated that a larger mesh net could be created for less than a dollar per square foot."
over 5 years ago
This short article supported by Sherry actually relates briefly on practical uses of the lotus effect. Because people are still not staisfied with or not sure whether it really works. So, anyone who have doubths or questions on this are welcome to ask me and to start a discussion in this page.
over 6 years ago
Excellent illustrations and explanation of this strategy:

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