Superhydrophobic hierarchically structured surfaces in biology: evolution, structural principles and biomimetic applications

Barthlott, Wilhelm; Mail, Matthias; Neinhuis, Christoph

doi:10.1098/rsta.2016.0191

Cited by 166 publications

(196 citation statements)

References 152 publications

(300 reference statements)

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“…Because small water droplets form a nearly spherical shape, they roll off the surface at a tilted angle below 10° [8]. The report of this phenomenon in plants in the late 1990s [1] generated enormous interest in water-repellent and self-cleaning surfaces, and led to innovations in artificial super-hydrophobic materials and surface coatings [9, 10]. However, there are many drawbacks in the production of such materials, and especially the durability of such coatings is often not satisfying [10].…”

Section: Introductionmentioning

confidence: 99%

Whip spiders (Amblypygi) become water-repellent by a colloidal secretion that self-assembles into hierarchical microstructures

et al. 2016

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BackgroundAmong both plants and arthropods, super-hydrophobic surfaces have evolved that enable self-cleaning, locomotion on water surfaces, or plastron respiration. Super-hydrophobicity is achieved by a combination of non-polar substances and complex micro- and nano-structures, usually acquired by growing processes or the deposition of powder-like materials.ResultsHere we report on a multi-phasic secretion in whip spiders (Arachnida, Amblypygi), which externally forms durable, hierarchical microstructures on the basically smooth cuticle. The solidified secretion crust makes the previously highly wettable cuticle super-hydrophobic. We describe the ultrastructure of secretory cells, and the maturation and secretion of the different products involved.ConclusionWhip spiders represent intriguing objects of study for revealing the mechanisms of the formation of complex microstructures in non-living systems. Understanding the physical and chemical processes involved may, further, be of interest for bio-inspired design of functional surface coatings.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-016-0059-y) contains supplementary material, which is available to authorized users.

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Section: Introductionmentioning

confidence: 99%

Whip spiders (Amblypygi) become water-repellent by a colloidal secretion that self-assembles into hierarchical microstructures

et al. 2016

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“…[1] However, passive techniques are preferred over active techniques as no additional energy is required. Nature provided us with two excellent examples of friction drag-reducing surfaces that utilize passive techniques: air-retaining water fern salvinia [2] and dermal denticle covered sharkskin. [3] The salvinia leaf is covered with hairy structures as shown in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

2017

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Salvinia leaf and sharkskin are prime examples of nature's marvel. Salvinia leaf‐inspired superhydrophobic surfaces keep themselves clean and reduce drag in fluid flow. Sharkskin also reduces drag in turbulent flow and inhibits biofouling. Therefore, the prospect of having a drag‐reducing surface with both salvinia leaf and sharkskin properties is attractive. However, fabricating such a surface is difficult, and the current fabrication methods require at least two separate steps. In addition, the mechanisms of drag reduction of salvinia leaf and sharkskin are different, and their combined effect on the flow field is not well understood. In this study, we produced a PTFE surface that mimics sharkskin in its surface pattern and copies the superhydrophobic nature of the salvinia leaf in its microstructure. This surface was fabricated by laser machining and tested in a closed channel under turbulent flow conditions. We measured the pressure drop at different Reynolds numbers on this surface both in pre‐wet and non‐pre‐wet conditions and compared the result with pressure drop data on four other PTFE samples: two types of non‐superhydrophobic sharkskin inspired surface (riblets), a superhydrophobic surface, and a non‐machined surface. Both the non‐superhydrophobic riblets and the superhydrophobic sample reduced drag compared to the non‐machined surface. However, we observed a lack of drag reduction by the superhydrophobic riblets sample. We presented a qualitative explanation for the lack of drag reduction and concluded that the modifications of the flow field by the two drag reduction mechanisms are not beneficial for overall drag reduction in our experiment.

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“…Superhydrophobic surfaces are not known in abiotic natural materials and evolved only in living organisms, e.g., in plants since the occupation of land some 450 million years ago . The most stable superhydrophobicity in plants is a result of hierarchical structuring of their surfaces and nanotubular structures with a diameter of 110 nm by the fatty secondary alcohol Nonacosan‐10‐ol like in the leaves of lotus . The function of this superhydrophobicity is predominantly anticontamination: microorganisms (e.g., fungal spores) hardly colonize these nonwettable surfaces.…”

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“…All superhydrophobic surfaces retain thin air layers (in lotus ≈15 µm) when immersed in water. For various ecological adaptations like gas exchange or drag reduction, semiaquatic plants have evolved the ability to retain thick (up to 3.5 mm or more) persistent air layers by complex hierarchical structuring ( Salvinia effect) . The ultimate example is the highly complex and sophisticated surface of the floating fern Salvinia molesta , which additionally exhibits chemical heterogeneities by superhydrophilic anchor cells to pin the air–water interface .…”

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“…The trapped air layer gives a silvery sheen appearance to its body due to the total reflection of light at the air–water interface. Apart from serving as a slip agent, reducing the drag of the backswimmer, this air layer provides a sensory function and probably serves as camouflage (similar to the silvery reflecting water surface) . Such surfaces are technologically interesting for applications like fluid drag reduction, antifouling, thermal isolation, and motion and pressure sensors …”

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Superhydrophobic Vertically Aligned Carbon Nanotubes for Biomimetic Air Retention under Water (Salvinia Effect)

Babu

Mail

Barthlott

et al. 2017

Adv Materials Inter

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The Salvinia effect refers to the stable retention of an air layer when submerged in water and is a result of complex hierarchical structuring, ultimate example of which is the surface of the floating fern Salvinia molesta. The air retention capability is technologically interesting as the retained air layer reduces drag force, prevents biofouling, and serves sensory functions. Air retention on artificial materials is currently limited to very few materials and is often a result of micrometer sized surface structures obtained by complex lithography techniques. In the present work, the air retention capabilities of superhydrophobic vertically aligned carbon nanotubes (VACNTs) are explored for the first time and the retained air layer is characterized by atomic force microscopy and confocal microscopy techniques. While the as‐prepared VACNTs retained only small pockets of air when submerged in water, superhydrophobic and regrown VACNT structures are found to be capable of retaining a continuous thick layer over extended period of time. The stable air retention capabilities of these nanostructured VACNT surfaces hold promising pathways for the development of biomimetic sensor systems.

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Superhydrophobic hierarchically structured surfaces in biology: evolution, structural principles and biomimetic applications

Abstract: One contribution of 12 to a theme issue 'Bioinspired hierarchically structured surfaces for green science' .

Cited by 166 publications

References 152 publications

Whip spiders (Amblypygi) become water-repellent by a colloidal secretion that self-assembles into hierarchical microstructures

Whip spiders (Amblypygi) become water-repellent by a colloidal secretion that self-assembles into hierarchical microstructures

Drag on superhydrophobic sharkskin inspired surface in a closed channel turbulent flow

Superhydrophobic Vertically Aligned Carbon Nanotubes for Biomimetic Air Retention under Water (Salvinia Effect)

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