The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
Wilhelm Barthlott - One of the best experts on this subject based on the ideXlab platform.
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Air Retention under water by the floating fern salvinia the crucial role of a trapped Air layer as a pneumatic spring
Small, 2020Co-Authors: Daniel Gandyra, Wilhelm Barthlott, Stanislav N. Gorb, Petra Ditsche, Stefan Walheim, Thomas SchimmelAbstract:The ability of floating ferns Salvinia to keep a permanent layer of Air under water is of great interest, e.g., for drag-reducing ship coatings. The Air-retaining hAirs are superhydrophobic, but have hydrophilic tips at their ends, pinning the Air-water interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for Air-layer stability under pressure changes. By applying the capillary adhesion technique, the adhesion forces of individual hAirs to the water surface is determined to be about 20 µN per hAir. Using confocal microscopy and fluorescence labeling, it is found that the leaves maintain a stable Air layer up to an underpressure of 65 mbar. Combining both results, overall pinning forces are obtained, which account for only about 1% of the total Air-retaining force. It is suggested that the restoring force of the entrapped Air layer is responsible for the remaining 99%. This model of the entrapped Air acting is verified as a pneumatic spring ("Air-spring") by an experiment shortcircuiting the Air layer, which results in immediate Air loss. Thus, the plant enhances its Air-layer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped Air volume as an elastic spring.
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Superhydrophobic Vertically Aligned Carbon Nanotubes for Biomimetic Air Retention under Water (Salvinia Effect)
Advanced Materials Interfaces, 2017Co-Authors: Deepu J Babu, Matthias Mail, Wilhelm Barthlott, Jorg J SchneiderAbstract: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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Plant Surfaces: Structures and Functions for Biomimetic Innovations
Nano-Micro Letters, 2017Co-Authors: Wilhelm Barthlott, Bharath Bhushan, Matthias Mail, Kerstin KochAbstract:An overview of plant surface structures and their evolution is presented. It combines surface chemistry and architecture with their functions and refers to possible biomimetic applications. Within some 3.5 billion years biological species evolved highly complex multifunctional surfaces for interacting with their environments: some 10 million living prototypes (i.e., estimated number of existing plants and animals) for engineers. The complexity of the hierarchical structures and their functionality in biological organisms surpasses all abiotic natural surfaces: even superhydrophobicity is restricted in nature to living organisms and was probably a key evolutionary step with the invasion of terrestrial habitats some 350–450 million years ago in plants and insects. Special attention should be paid to the fact that global environmental change implies a dramatic loss of species and with it the biological role models. Plants, the dominating group of organisms on our planet, are sessile organisms with large multifunctional surfaces and thus exhibit particular intriguing features. Superhydrophilicity and superhydrophobicity are focal points in this work. We estimate that superhydrophobic plant leaves (e.g., grasses) comprise in total an area of around 250 million km2, which is about 50% of the total surface of our planet. A survey of structures and functions based on own examinations of almost 20,000 species is provided, for further references we refer to Barthlott et al. (Philos. Trans. R. Soc. A 374: 20160191, 1). A basic difference exists between aquatic non-vascular and land-living vascular plants; the latter exhibit a particular intriguing surface chemistry and architecture. The diversity of features is described in detail according to their hierarchical structural order. The first underlying and essential feature is the polymer cuticle superimposed by epicuticular wax and the curvature of single cells up to complex multicellular structures. A descriptive terminology for this diversity is provided. Simplified, the functions of plant surface characteristics may be grouped into six categories: (1) mechanical properties, (2) influence on reflection and absorption of spectral radiation, (3) reduction of water loss or increase of water uptake, moisture harvesting, (4) adhesion and non-adhesion (lotus effect, insect trapping), (5) drag and turbulence increase, or (6) Air Retention under water for drag reduction or gas exchange (Salvinia effect). This list is far from complete. A short overview of the history of bionics and the impressive spectrum of existing and anticipated biomimetic applications are provided. The major challenge for engineers and materials scientists, the durability of the fragile nanocoatings, is also discussed.
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elasticity of the hAir cover in Air retaining salvinia surfaces
Applied Physics A, 2015Co-Authors: Elena V Gorb, Stanislav N. Gorb, Petra Ditsche, Matthias Mayser, Thomas Schimmel, Wilhelm BarthlottAbstract:Immersed in water superhydrophobic surfaces (e.g., lotus) maintain thin temporary Air films. In certain aquatic plants and animals, these films are thicker and more persistent. Floating ferns of the genus Salvinia show elaborated hierarchical superhydrophobic surface structures: a hAiry cover of complex trichomes. In the case of S. molesta, they are eggbeater shaped and topped by hydrophilic tips, which pin the Air-water interface and prevent rupture of contact. It has been proposed that these trichomes can oscillate with the Air-water interface, when turbulences occur and thereby stabilize the Air film. The deformability of such arrays of trichomes requires a certain elasticity of the structures. In this study, we determined the stiffness of the trichome coverage of S. molesta and three other Salvinia species. Our results confirm the elasticity of the trichome coverage in all investigated Salvinia species. We did not reveal a clear relationship between the time of Air Retention and stiffness of the trichome coverage, which means that the Air Retention function is additionally dependent on different parameters, e.g., the trichome shape and surface free energy. These data are not only interesting for Salvinia biology, but also important for the development of biomimetic Air-retaining surfaces.
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dry under water comparative morphology and functional aspects of Air retaining insect surfaces
Journal of Morphology, 2011Co-Authors: Alexander Balmert, Petra Ditschekuru, Holger F Bohn, Wilhelm BarthlottAbstract:Superhydrophobic surfaces prevent certain body parts of semiaquatic and aquatic insects from getting wet while submerged in water. The Air layer on these surfaces can serve the insects as a physical gill. Using scanning electron microscopy, we investigated the morphology of Air-retaining surfaces in five insect species with different levels of adaptation to aquatic habitats. We found surfaces with either large and sparse hAirs (setae), small and dense hAirs (microtrichia), or hierarchically structured surfaces with both types of hAirs. The structural parameters and Air-film persistence of these surfaces were compared. Air-film persistence varied between 2 days in the beetle Galerucella nymphaea possessing only sparse setae and more than 120 days in the bugs Notonecta glauca and Ilyocoris cimicoides possessing dense microtrichia (up to 6.6 × 106 microtrichia per millimeter square). From our results, we conclude that the density of the surface structures is the most important factor that affects the persistence of Air films. Combinations of setae and microtrichia are not decisive for the overall persistence of the Air film but might provide a thick Air store for a short time and a thin but mechanically more stable Air film for a long time. Thus, we assume that a dense cover of microtrichia acts as a “backup system” preventing wetting of the body surface in case the Air–water interface is pressed toward the surface. Our findings might be beneficial for the development of biomimetic surfaces for long-term Air Retention and drag reduction under water. In addition, the biological functions of the different Air Retention capabilities are discussed. J. Morphol., 2011. © 2011 Wiley-Liss, Inc.
Cho-yun Yang - One of the best experts on this subject based on the ideXlab platform.
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Superhydrophobic, antiadhesive, and antireflective surfaces mediated by hybrid biomimetic salvinia leaf with moth-eye structures
Applied Physics Express, 2014Co-Authors: Cho-yun Yang, Cho-yu Yang, Cheng-kuo Sung, Yu-lin Tsai, Peichen YuAbstract:In this paper, we successfully demonstrate multifunctional surfaces based on scaffolding biomimetic structures, namely, hybrid salvinia leaves with moth-eye structures (HSMSs). The novel fabrication process employs scalable polystyrene nanosphere lithography and a lift-off process. Systematic characterizations show the biomimetic HSMS exhibiting superhydrophobic, self-cleaning, antiadhesive, and antireflective properties. Furthermore, the resulting surface tension gradient (known as the Marangoni effect) leads to a superior Air Retention characteristic in the HSMS under water droplet impact, compared with the traditional hybrid lotus leaf with a moth-eye structure (HLMS). Such results and learnings pave the way towards the attainment and mass deployment of dielectric surfaces with multiple functionalities for versatile biological and optoelectronic applications.
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enhancing Air Retention by biomimicking salvinia molesta structures
Japanese Journal of Applied Physics, 2013Co-Authors: Cho-yun Yang, Cho-yu Yang, Cheng-kuo SungAbstract:The Air-retaining property of the hydrophobic surface can be widely employed in many applications. This study is carried out to enhance this property by biomimicking the structure of Salvinia molesta floating leaves, which features hydrophilic patches on a superhydrophobic structure. Different from the existing lotus structure, in this study, the theoretical models and equations governing the contact and sliding angles, and contact line density of the salvinia structure were developed. The Marangoni effect was re-examined and modified to consider the characteristic of the salvinia structure. In addition, a novel process was proposed to fabricate the salvinia and lotus structures, which were designed using mathematical models and numerical simulation results. Both structures were tested to verify the theoretical models and derived governing equations. The results indicate that the Air-retaining property was greatly enhanced using the salvinia structure compared with the lotus one.
Cheng-kuo Sung - One of the best experts on this subject based on the ideXlab platform.
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Superhydrophobic, antiadhesive, and antireflective surfaces mediated by hybrid biomimetic salvinia leaf with moth-eye structures
Applied Physics Express, 2014Co-Authors: Cho-yun Yang, Cho-yu Yang, Cheng-kuo Sung, Yu-lin Tsai, Peichen YuAbstract:In this paper, we successfully demonstrate multifunctional surfaces based on scaffolding biomimetic structures, namely, hybrid salvinia leaves with moth-eye structures (HSMSs). The novel fabrication process employs scalable polystyrene nanosphere lithography and a lift-off process. Systematic characterizations show the biomimetic HSMS exhibiting superhydrophobic, self-cleaning, antiadhesive, and antireflective properties. Furthermore, the resulting surface tension gradient (known as the Marangoni effect) leads to a superior Air Retention characteristic in the HSMS under water droplet impact, compared with the traditional hybrid lotus leaf with a moth-eye structure (HLMS). Such results and learnings pave the way towards the attainment and mass deployment of dielectric surfaces with multiple functionalities for versatile biological and optoelectronic applications.
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enhancing Air Retention by biomimicking salvinia molesta structures
Japanese Journal of Applied Physics, 2013Co-Authors: Cho-yun Yang, Cho-yu Yang, Cheng-kuo SungAbstract:The Air-retaining property of the hydrophobic surface can be widely employed in many applications. This study is carried out to enhance this property by biomimicking the structure of Salvinia molesta floating leaves, which features hydrophilic patches on a superhydrophobic structure. Different from the existing lotus structure, in this study, the theoretical models and equations governing the contact and sliding angles, and contact line density of the salvinia structure were developed. The Marangoni effect was re-examined and modified to consider the characteristic of the salvinia structure. In addition, a novel process was proposed to fabricate the salvinia and lotus structures, which were designed using mathematical models and numerical simulation results. Both structures were tested to verify the theoretical models and derived governing equations. The results indicate that the Air-retaining property was greatly enhanced using the salvinia structure compared with the lotus one.
Petra Ditsche - One of the best experts on this subject based on the ideXlab platform.
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Air Retention under water by the floating fern salvinia the crucial role of a trapped Air layer as a pneumatic spring
Small, 2020Co-Authors: Daniel Gandyra, Wilhelm Barthlott, Stanislav N. Gorb, Petra Ditsche, Stefan Walheim, Thomas SchimmelAbstract:The ability of floating ferns Salvinia to keep a permanent layer of Air under water is of great interest, e.g., for drag-reducing ship coatings. The Air-retaining hAirs are superhydrophobic, but have hydrophilic tips at their ends, pinning the Air-water interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for Air-layer stability under pressure changes. By applying the capillary adhesion technique, the adhesion forces of individual hAirs to the water surface is determined to be about 20 µN per hAir. Using confocal microscopy and fluorescence labeling, it is found that the leaves maintain a stable Air layer up to an underpressure of 65 mbar. Combining both results, overall pinning forces are obtained, which account for only about 1% of the total Air-retaining force. It is suggested that the restoring force of the entrapped Air layer is responsible for the remaining 99%. This model of the entrapped Air acting is verified as a pneumatic spring ("Air-spring") by an experiment shortcircuiting the Air layer, which results in immediate Air loss. Thus, the plant enhances its Air-layer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped Air volume as an elastic spring.
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elasticity of the hAir cover in Air retaining salvinia surfaces
Applied Physics A, 2015Co-Authors: Elena V Gorb, Stanislav N. Gorb, Petra Ditsche, Matthias Mayser, Thomas Schimmel, Wilhelm BarthlottAbstract:Immersed in water superhydrophobic surfaces (e.g., lotus) maintain thin temporary Air films. In certain aquatic plants and animals, these films are thicker and more persistent. Floating ferns of the genus Salvinia show elaborated hierarchical superhydrophobic surface structures: a hAiry cover of complex trichomes. In the case of S. molesta, they are eggbeater shaped and topped by hydrophilic tips, which pin the Air-water interface and prevent rupture of contact. It has been proposed that these trichomes can oscillate with the Air-water interface, when turbulences occur and thereby stabilize the Air film. The deformability of such arrays of trichomes requires a certain elasticity of the structures. In this study, we determined the stiffness of the trichome coverage of S. molesta and three other Salvinia species. Our results confirm the elasticity of the trichome coverage in all investigated Salvinia species. We did not reveal a clear relationship between the time of Air Retention and stiffness of the trichome coverage, which means that the Air Retention function is additionally dependent on different parameters, e.g., the trichome shape and surface free energy. These data are not only interesting for Salvinia biology, but also important for the development of biomimetic Air-retaining surfaces.
Thomas Schimmel - One of the best experts on this subject based on the ideXlab platform.
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Air Retention under water by the floating fern salvinia the crucial role of a trapped Air layer as a pneumatic spring
Small, 2020Co-Authors: Daniel Gandyra, Wilhelm Barthlott, Stanislav N. Gorb, Petra Ditsche, Stefan Walheim, Thomas SchimmelAbstract:The ability of floating ferns Salvinia to keep a permanent layer of Air under water is of great interest, e.g., for drag-reducing ship coatings. The Air-retaining hAirs are superhydrophobic, but have hydrophilic tips at their ends, pinning the Air-water interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for Air-layer stability under pressure changes. By applying the capillary adhesion technique, the adhesion forces of individual hAirs to the water surface is determined to be about 20 µN per hAir. Using confocal microscopy and fluorescence labeling, it is found that the leaves maintain a stable Air layer up to an underpressure of 65 mbar. Combining both results, overall pinning forces are obtained, which account for only about 1% of the total Air-retaining force. It is suggested that the restoring force of the entrapped Air layer is responsible for the remaining 99%. This model of the entrapped Air acting is verified as a pneumatic spring ("Air-spring") by an experiment shortcircuiting the Air layer, which results in immediate Air loss. Thus, the plant enhances its Air-layer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped Air volume as an elastic spring.
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elasticity of the hAir cover in Air retaining salvinia surfaces
Applied Physics A, 2015Co-Authors: Elena V Gorb, Stanislav N. Gorb, Petra Ditsche, Matthias Mayser, Thomas Schimmel, Wilhelm BarthlottAbstract:Immersed in water superhydrophobic surfaces (e.g., lotus) maintain thin temporary Air films. In certain aquatic plants and animals, these films are thicker and more persistent. Floating ferns of the genus Salvinia show elaborated hierarchical superhydrophobic surface structures: a hAiry cover of complex trichomes. In the case of S. molesta, they are eggbeater shaped and topped by hydrophilic tips, which pin the Air-water interface and prevent rupture of contact. It has been proposed that these trichomes can oscillate with the Air-water interface, when turbulences occur and thereby stabilize the Air film. The deformability of such arrays of trichomes requires a certain elasticity of the structures. In this study, we determined the stiffness of the trichome coverage of S. molesta and three other Salvinia species. Our results confirm the elasticity of the trichome coverage in all investigated Salvinia species. We did not reveal a clear relationship between the time of Air Retention and stiffness of the trichome coverage, which means that the Air Retention function is additionally dependent on different parameters, e.g., the trichome shape and surface free energy. These data are not only interesting for Salvinia biology, but also important for the development of biomimetic Air-retaining surfaces.