The Experts below are selected from a list of 345 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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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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SYMPOSIUM Layers of Air in the Water beneath the Floating Fern Salvinia are Exposed to Fluctuations in Pressure
2016Co-Authors: Matthias Mayser, Wilhelm BarthlottAbstract:Synopsis Superhydrophobic, hierarchically structured, technical surfaces (Lotus-Effect) are of high scientific and eco-nomic interest because of their remarkable properties. Recently, the immense potential of air-retaining superhydrophobic surfaces, for example, for low-friction transport of fluids and drag-reducing coatings of ships has begun to be explored. A major problem of superhydrophobic surfaces mimicking the Lotus-Effect is the limited persistence of the air retained, especially under rough conditions of flow. However, there are a variety of floating or diving plant and animal species that possess air-retaining surfaces optimized for durable water-repellency (Salvinia-Effect). Especially floating ferns of the genus Salvinia have evolved superhydrophobic surfaces capable of maintaining layers of air for months. Apart from maintaining stability under water, the layer of air has to withstand the stresses of water pressure (up to 2.5 bars). Both of these aspects have an application to create permanent air layers on ships ’ hulls. We investigated the Effect of pressure on air layers in a pressure cell and exposed the air layer to pressures of up to 6 bars. We investigated the suppression of the air layer at increasing pressures as well as its restoration during decreases in pressure. Three of the four examined Salvinia species are capable of maintaining air layers at pressures relevant to the conditions applying to ships ’ hulls. High volumes of air per surface area are advantageous for retaining at least a partial Cassie–Baxter-state under pressure, which also helps in restoring the air layer after depressurization. Closed-loop structures such as the baskets at the top of the ‘‘egg-beate
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layers of air in the water beneath the floating fern salvinia are exposed to fluctuations in pressure
Integrative and Comparative Biology, 2014Co-Authors: Matthias Mayser, Wilhelm BarthlottAbstract:Superhydrophobic, hierarchically structured, technical surfaces (Lotus-Effect) are of high scientific and economic interest because of their remarkable properties. Recently, the immense potential of air-retaining superhydrophobic surfaces, for example, for low-friction transport of fluids and drag-reducing coatings of ships has begun to be explored. A major problem of superhydrophobic surfaces mimicking the Lotus-Effect is the limited persistence of the air retained, especially under rough conditions of flow. However, there are a variety of floating or diving plant and animal species that possess air-retaining surfaces optimized for durable water-repellency (Salvinia-Effect). Especially floating ferns of the genus Salvinia have evolved superhydrophobic surfaces capable of maintaining layers of air for months. Apart from maintaining stability under water, the layer of air has to withstand the stresses of water pressure (up to 2.5 bars). Both of these aspects have an application to create permanent air layers on ships' hulls. We investigated the Effect of pressure on air layers in a pressure cell and exposed the air layer to pressures of up to 6 bars. We investigated the suppression of the air layer at increasing pressures as well as its restoration during decreases in pressure. Three of the four examined Salvinia species are capable of maintaining air layers at pressures relevant to the conditions applying to ships' hulls. High volumes of air per surface area are advantageous for retaining at least a partial Cassie-Baxter-state under pressure, which also helps in restoring the air layer after depressurization. Closed-loop structures such as the baskets at the top of the "egg-beater hairs" (see main text) also help return the air layer to its original level at the tip of the hairs by trapping air bubbles.
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Lotus-Effect®: Biomimetic Super-Hydrophobic Surfaces and their Application
Advances in Science and Technology, 2008Co-Authors: Manuel Spaeth, Wilhelm BarthlottAbstract:The majority of organismic surfaces, like the plant cuticle, is not smooth but micro-structured. Moreover, they are often covered with hydrophobic wax crystals, some hundred nm in size. The combination of micro- and nanostructures, together with a hydrophobic chemistry, generates the phenomenon of super-hydrophobicity: Water-droplets on such surfaces exhibit contact angles above 140°. Furthermore, dirt particles can barely adhere and are removed by running water only, hence they are called ‘self-cleaning’. The underlying physico-chemical principles were successfully applied to technical prototypes. This technical conversion was patented and the trade mark Lotus-Effect® was introduced in the mid 1990s. Since then several Lotus-Effect® products like a façade paint, a glass coating or a spray were introduced. Another area of application for which prototypes exist, are textiles for awnings, tents or other outdoor purposes. Recently a different aspect of such surfaces is investigated: structures retaining air under water. Several floating plants and semiaquatic animals show this ability. The aim of this project is to develop technical surfaces for long time application in ships and pipelines, as an air film between surface and liquid leads to drag reduction and thus savings of energy.
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wetting and self cleaning properties of artificial superhydrophobic surfaces
Langmuir, 2005Co-Authors: Reiner Furstner, Wilhelm Barthlott, Christoph Neinhuis, Peter WalzelAbstract:The wetting and the self-cleaning properties (the latter is often called the “Lotus-Effect”) of three types of superhydrophobic surfaces have been investigated: silicon wafer specimens with different regular arrays of spikes hydrophobized by chemical treatment, replicates of water-repellent leaves of plants, and commercially available metal foils which were additionally hydrophobized by means of a fluorinated agent. Water droplets rolled off easily from those silicon samples which had a microstructure consisting of rather slender spikes with narrow pitches. Such samples could be cleaned almost completely from artificial particulate contaminations by a fog consisting of water droplets (diameter range, 8−20 μm). Some metal foils and some replicates had two levels of roughening. Because of this, a complete removal of all particles was not possible using artificial fog. However, water drops with some amount of kinetic impact energy were able to clean these surfaces perfectly. A substrate where pronounced str...
Lei Jiang - One of the best experts on this subject based on the ideXlab platform.
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adhesion tuning at superhydrophobic states from petal Effect to Lotus Effect
Macromolecular Materials and Engineering, 2015Co-Authors: Guangming Gong, Lei Jiang, Xu JinAbstract:The influence of the micro topology on the solid/water wetting and adhesion behaviors is studied in this work. By simply tailoring the morphology, superhydrophobicity can be achieved on a weak hydrophobic surface. And the further fine-tuning of the surficial geometry realizes the conversion of superhydrophobic states, from Petal to Lotus Effect. The experimental data indicates that the key factor that distinguishing these two states lies in the number of solid/liquid interfaces. This work provides an answer to the fundamental study of the wetting phenomena and it is a complementary to current understanding of special wettings as well.
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petal Effect a superhydrophobic state with high adhesive force
Langmuir, 2008Co-Authors: Lin Feng, Nü Wang, Yanan Zhang, Jinming Xi, Lei JiangAbstract:Hierarchical micropapillae and nanofolds are known to exist on the petals' surfaces of red roses. These micro- and nanostructures provide a sufficient roughness for superhydrophobicity and yet at the same time a high adhesive force with water. A water droplet on the surface of the petal appears spherical in shape, which cannot roll off even when the petal is turned upside down. We define this phenomenon as the “petal Effect” as compared with the popular “Lotus Effect”. Artificial fabrication of biomimic polymer films, with well-defined nanoembossed structures obtained by duplicating the petal's surface, indicates that the superhydrophobic surface and the adhesive petal are in Cassie impregnating wetting state.
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microscale and nanoscale hierarchical structured mesh films with superhydrophobic and superoleophilic properties induced by long chain fatty acids
Nanotechnology, 2007Co-Authors: Shutao Wang, Yanlin Song, Lei JiangAbstract:Inspired by the Lotus Effect, we fabricate new microscale and nanoscale hierarchical structured copper mesh films by a simple electrochemical deposition. After modification of the long-chain fatty acid monolayer, these films show superhydrophobic and superoleophilic properties, which could be used for the Effective separation of oil and water. The length of the fatty acid chain strongly influences the surface wettability of as-prepared films. It is confirmed that the cooperative Effect of the hierarchical structure of the copper film and the nature of the long-chain fatty acid contribute to this unique surface wettability.
Joanna Aizenberg - One of the best experts on this subject based on the ideXlab platform.
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lubricant infused micro nano structured surfaces with tunable dynamic omniphobicity at high temperatures
Applied Physics Letters, 2013Co-Authors: Dan Daniel, Rebecca A Belisle, Max N Mankin, Tak Sing Wong, Joanna AizenbergAbstract:Omniphobic surfaces that can repel fluids at temperatures higher than 100 °C are rare. Most state-of-the-art liquid-repellent materials are based on the Lotus Effect, where a thin air layer is maintained throughout micro/nanotextures leading to high mobility of liquids. However, such behavior eventually fails at elevated temperatures when the surface tension of test liquids decreases significantly. Here, we demonstrate a class of lubricant-infused structured surfaces that can maintain a robust omniphobic state even for low-surface-tension liquids at temperatures up to at least 200 °C. We also demonstrate how liquid mobility on such surfaces can be tuned by a factor of 1000.
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bioinspired self repairing slippery surfaces with pressure stable omniphobicity
Nature, 2011Co-Authors: Tak Sing Wong, Elizabeth J. Smythe, Alison Grinthal, Benjamin Hatton, Sindy K Y Tang, Sung Hoon Kang, Joanna AizenbergAbstract:Inspired by the insect-eating Nepenthes pitcher plant, which snares its prey on a surface lubricated by a remarkably slippery aqueous secretion, Joanna Aizenberg and colleagues have synthesized omniphobic surfaces that can self-repair and function at high pressures. Their 'slippery liquid-infused porous surfaces' (or SLIPS) exhibit almost perfect slipperiness towards polar, organic and complex liquids. SLIPS function under extreme conditions, are easily constructed from inexpensive materials and can be endowed with other useful characteristics, such as enhanced optical transparency, through the selection of appropriate substrates and lubricants. Ultra-slippery surfaces of this type might find application in biomedical fluid handling, fuel transport, antifouling, anti-icing, optical imaging and elsewhere. Creating a robust synthetic surface that repels various liquids would have broad technological implications for areas ranging from biomedical devices and fuel transport to architecture but has proved extremely challenging1. Inspirations from natural nonwetting structures2,3,4,5,6, particularly the leaves of the Lotus, have led to the development of liquid-repellent microtextured surfaces that rely on the formation of a stable air–liquid interface7,8,9. Despite over a decade of intense research, these surfaces are, however, still plagued with problems that restrict their practical applications: limited oleophobicity with high contact angle hysteresis9, failure under pressure10,11,12 and upon physical damage1,7,11, inability to self-heal and high production cost1,11. To address these challenges, here we report a strategy to create self-healing, slippery liquid-infused porous surface(s) (SLIPS) with exceptional liquid- and ice-repellency, pressure stability and enhanced optical transparency. Our approach—inspired by Nepenthes pitcher plants13—is conceptually different from the Lotus Effect, because we use nano/microstructured substrates to lock in place the infused lubricating fluid. We define the requirements for which the lubricant forms a stable, defect-free and inert ‘slippery’ interface. This surface outperforms its natural counterparts2,3,4,5,6 and state-of-the-art synthetic liquid-repellent surfaces8,9,14,15,16 in its capability to repel various simple and complex liquids (water, hydrocarbons, crude oil and blood), maintain low contact angle hysteresis (<2.5°), quickly restore liquid-repellency after physical damage (within 0.1–1 s), resist ice adhesion, and function at high pressures (up to about 680 atm). We show that these properties are insensitive to the precise geometry of the underlying substrate, making our approach applicable to various inexpensive, low-surface-energy structured materials (such as porous Teflon membrane). We envision that these slippery surfaces will be useful in fluid handling and transportation, optical sensing, medicine, and as self-cleaning and anti-fouling materials operating in extreme environments.
Bharat Bhushan - One of the best experts on this subject based on the ideXlab platform.
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biomimetics bioinspired hierarchical structured surfaces for green science and technology
2012Co-Authors: Bharat BhushanAbstract:From the Contents: Modeling of Contact Angle for a Liquid in Contact with a Rough Surface.- Part I: Lotus Effect.- Lotus Effect Surfaces in Nature.- How to Make Hierarchical Surfaces. Part II: Rose Petal Effect. Part III: Shark Skin Effect.- Shark-Skin Surfaces for Fluid-Drag Reduction in Turbulent Flow.- Fabrication and Characterization of Biomimetic Structures for Fluid Drag Reduction.
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green tribology biomimetics energy conservation and sustainability
2012Co-Authors: Mikhail Nosonovskiĭ, Bharat BhushanAbstract:Introduction.- Part One: Biomimetics.- Biomimetic surfaces: an overview.- Lotus Effect for non-adhesive surfaces.- Friction in living nature.- Biomimetic microstructured surfaces for dry friction.- Self-lubrication in nature and engineering.- Gecko-Effect.- Surface-healing composite materials.- Self-replenishing lubrication.- Part Two: Control of Friction and Wear.- Surface texturing for friction and wear control.- Solid lubrication.- Self-organization during friction.- Part Three: Environmental Aspects of Lubrication and Surface Modification.- Environmentally-friendly lubricants: biodegradable and non-toxic.- Environmental aspects of the Lotus Effect and surface microstructuring.- Self-cleaning polymeric surfaces.- Self-cleaning metallic surfaces.- Antifouling surfaces: environmental aspects.- Part Four: Green Applications.- Tribology of wind power turbines.- Self-cleaning solar panel coatings.- Surface modification and new ways of energy transition.- Closure.
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Lotus Effect surfaces in nature
2012Co-Authors: Bharat BhushanAbstract:Many biological surfaces are known to be superhydrophobic and self-cleaning with low adhesion/low drag. They also exhibit antifouling properties. In this chapter, various plant leaves, their roughness, and wax coatings in relation to their hydrophobic/hydrophilic and self-cleaning properties (Bhushan and Jung, 2011) will be discussed. Surface characterization of hydrophobic and hydrophilic leaves on the micro- and nanoscale is presented to understand the role of microbumps and nanobumps. In addition, the contact angle and adhesion and friction properties of these leaves are considered. The knowledge gained by examining these properties of the leaves and by quantitatively analyzing the surface structure will help in the design of superhydrophobic and self-cleaning surfaces.
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Durable Lotus-Effect surfaces with hierarchical structure using micro- and nanosized hydrophobic silica particles
Journal of colloid and interface science, 2011Co-Authors: Daniel W. Ebert, Bharat BhushanAbstract:Abstract Surfaces with a very high apparent water contact angle (CA) and low water contact angle hysteresis (CAH) exhibit many useful characteristics, among them extreme water repellency, low drag for fluid flow, and a self-cleaning Effect. The leaf of the Lotus plant ( Nelumbo nucifera ) achieves these properties using a hierarchical structure with roughness on both the micro- and nanoscale. It is of great interest to create durable surfaces with the so-called “Lotus Effect” for many important applications. In this study, hierarchically structured surfaces with Lotus-Effect properties were fabricated using micro- and nanosized hydrophobic silica particles and a simple spray method. In addition, hierarchically structured surfaces were prepared by spraying a nanoparticulate coating over a micropatterned surface. To examine the similarities between surfaces using microparticles versus a uniform micropattern as the microstructure, CA and CAH were compared across a range of pitch values for the two types of microstructures. Wear experiments were performed using an atomic force microscope (AFM), a ball-on-flat tribometer, and a water jet apparatus to verify multiscale wear resistance. These surfaces have potential uses in engineering applications requiring Lotus-Effect properties and high durability.
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natural and biomimetic artificial surfaces for superhydrophobicity self cleaning low adhesion and drag reduction
Progress in Materials Science, 2011Co-Authors: Bharat Bhushan, Yong Chae JungAbstract:Abstract Nature has developed materials, objects, and processes that function from the macroscale to the nanoscale. The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature to provide properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as Lotus leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical roughness of their leaf surfaces. The self-cleaning phenomenon is widely known as the “Lotus Effect.” These surfaces with high contact angle and low contact angle hysteresis with a self-cleaning Effect also exhibit low adhesion and drag reduction for fluid flow. In this article, the theoretical mechanisms of the wetting of rough surfaces are presented followed by the characterization of natural leaf surfaces. The next logical step is to realize superhydrophobic surfaces based on understanding of the leaves. Next, a comprehensive review is presented on artificial superhydrophobic surfaces fabricated using various fabrication techniques and the influence of micro-, nano- and hierarchical structures on superhydrophobicity, self-cleaning, low adhesion, and drag reduction.
Abraham Marmur - One of the best experts on this subject based on the ideXlab platform.
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the role of multiscale roughness in the Lotus Effect is it essential for super hydrophobicity
Langmuir, 2012Co-Authors: Eyal Bittoun, Abraham MarmurAbstract:The role of multiscale (hierarchical) roughness in optimizing the structure of nonwettable (superhydrophobic) solid surfaces was theoretically studied for 2D systems of a drop on three different types of surface topographies with up to four roughness scales. The surface models considered here were sinusoidal, flat-top pillars, and triadic Koch curves. Three criteria were used to compare between the various topographies and roughness scales. The first is the transition contact angle (CA) between the Wenzel (W) and Cassie–Baxter (CB) wetting states, above which the CB state is the thermodynamically stable one. The second is the solid–liquid (wetted) interfacial area, as an indicator for the ease of roll-off of a drop from the superhydrophobic surfaces. The third is the protrusion height that reflects the mechanical stability of the surface against breakage. The results indicate that multiscale roughness per se is not essential for superhydrophobicity; however, it mainly decreases the necessary protrusion he...
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super hydrophobicity fundamentals implications to biofouling prevention
Biofouling, 2006Co-Authors: Abraham MarmurAbstract:The theory of wetting on super-hydrophobic surfaces is presented and discussed, within the general framework of equilibrium wetting and contact angles. Emphasis is put on the implications of super-hydrophobicity to the prevention of biofouling. Two main lines of thought are discussed, viz. i) "mirror imaging" of the Lotus Effect, namely designing a surface that repels biological entities by being super-hydrophilic, and ii) designing a surface that minimises the water-wetted area when submerged in water (by keeping an air film between the water and the surface), so that the suspended biological entities have a low probability of encountering the solid surface.
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The Lotus Effect: Superhydrophobicity and Metastability
Langmuir, 2004Co-Authors: Abraham MarmurAbstract:To learn how to mimic the Lotus Effect, superhydrophobicity of a model system that resembles the Lotus leaf is theoretically discussed. Superhydrophobicity is defined by two criteria: a very high water contact angle and a very low roll-off angle. Since it is very difficult to calculate the latter for rough surfaces, it is proposed here to use the criterion of a very low wet (solid−liquid) contact area as a simple, approximate substitute for the roll-off angle criterion. It is concluded that nature employs metastable states in the heterogeneous wetting regime as the key to superhydrophobicity on Lotus leaves. This strategy results in two advantages: (a) it avoids the need for high steepness protrusions that may be sensitive to breakage and (b) it lowers the sensitivity of the superhydrophobic states to the protrusion distance.
