scholarly journals Air retaining grids—a novel technology to maintain stable air layers under water for drag reduction

2019 ◽  
Vol 377 (2150) ◽  
pp. 20190126 ◽  
Author(s):  
M. Mail ◽  
M. Moosmann ◽  
P. Häger ◽  
W. Barthlott
Keyword(s):  
Drag Reduction ◽  
Stable Solution ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Lotus Effect ◽  
Ship Hulls ◽  
First Results ◽  
Air Layers ◽  
Micro Pillars

Extreme water repellent ‘superhydrophobic’ surfaces evolved in plants and animals about 450 Ma: a combination of hydrophobic chemistry and hierarchical structuring causes contact angles of greater than 150°. Technical biomimetic applications and technologies for water repellency, self-cleaning (Lotus Effect) and drag reduction (Salvinia Effect) have become increasingly important in the last two decades. Drag reduction (e.g. for ship hulls) requires the presence of a rather thick and persistent air layer under water. All existing technical solutions are based on fragile elastic hairs, micro-pillars or other solitary structures, preferably with undercuts (Salvinia Effect). We propose and provide experimental data for a novel alternative technology to trap persistent air layers by superhydrophobic grids or meshes superimposed to the solid surface: AirGrids. AirGrids provide a simple and stable solution to generate air trapping surfaces for drag reduction under water as demonstrated by first prototypes. Different architectural solutions, including possible recovery techniques for the air layer under hydrodynamic conditions, are discussed. The most promising target backed by first results is the combination of Air Retaining Grids with the existing microbubble technology. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 2)’.

scholarly journals Superhydrophobicity in perfection: the outstanding properties of the lotus leaf

2011 ◽  
Vol 2 ◽  
pp. 152-161 ◽  
Author(s):  
Hans J Ensikat ◽  
Petra Ditsche-Kuru ◽  
Christoph Neinhuis ◽  
Wilhelm Barthlott
Keyword(s):  
Chemical Composition ◽  
Water Repellency ◽  
Contact Angles ◽  
Dense Layer ◽  
Lotus Effect ◽  
Nano Structure ◽  
Lotus Leaf ◽  
Water Drops ◽  
The Impact ◽  
Unique Chemical

Lotus leaves have become an icon for superhydrophobicity and self-cleaning surfaces, and have led to the concept of the ‘Lotus effect’. Although many other plants have superhydrophobic surfaces with almost similar contact angles, the lotus shows better stability and perfection of its water repellency. Here, we compare the relevant properties such as the micro- and nano-structure, the chemical composition of the waxes and the mechanical properties of lotus with its competitors. It soon becomes obvious that the upper epidermis of the lotus leaf has developed some unrivaled optimizations. The extraordinary shape and the density of the papillae are the basis for the extremely reduced contact area between surface and water drops. The exceptional dense layer of very small epicuticular wax tubules is a result of their unique chemical composition. The mechanical robustness of the papillae and the wax tubules reduce damage and are the basis for the perfection and durability of the water repellency. A reason for the optimization, particularly of the upper side of the lotus leaf, can be deduced from the fact that the stomata are located in the upper epidermis. Here, the impact of rain and contamination is higher than on the lower epidermis. The lotus plant has successfully developed an excellent protection for this delicate epistomatic surface of its leaves.

Development of multifunctional cotton fabric via chemical foam application method

2019 ◽  
Vol 90 (9-10) ◽  
pp. 991-1001 ◽  
Author(s):  
Zeynep Omerogullari Basyigit ◽  
Dilek Kut ◽  
Peter Hauser
Keyword(s):  
Cotton Fabric ◽  
Textile Industry ◽  
Performance Test ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Test Results ◽  
Important Place ◽  
Application Method ◽  
Color Spectrum

Nowadays, the methods and techniques used in the textile industry are required to be environmentally friendly, and water and energy saving. In addition to these, they should transfer more than one functionality, in other words give multifunctionality to the textile material with reliable and sufficient results in terms of efficiency and permanence. With the increase in and diversification of today's industrial requirements, one functionality on the fabric may be insufficient to meet the requirements, and therefore the subject of multifunctionality holds an important place in the textile industry. Therefore, in this study flame retardant, antibacterial and water-repellent, single-layered multifunctional 100% cotton fabrics with different functionalities on different sides (back and face surfaces) of the fabric were obtained via a chemical foam application method, which has many advantages compared with conventional methods. In some of the experimental parts, impregnation and foam application methods were combined in the process in order to optimize the multifunctionality properties of the fabrics. In order to indicate the performance test of cotton fabric, vertical burning test, contact angle test, antibacterial test against Gram positive and Gram negative bacteria, color spectrum analysis and tearing strength test were carried out while, in terms of characterization tests, Fourier transform infrared (attenuated total reflectance) and scanning electron microscope analyses were performed. According to the test results, the flame retardancy effect of the samples was improved significantly while antibacterial results showed a 99% reduction of bacteria and the finished fabrics demonstrated improved water repellency with contact angles up to 125°. In addition, the functionalities were durable up to 50 washing and 50 drying cycles.

PVDF Films with Superhydrophobic Surface Fabricated by Plasma-Enhanced Chemical Vapor Deposition

2009 ◽  
Vol 79-82 ◽  
pp. 1451-1454 ◽  
Author(s):  
Zhi Qiu Zhang ◽  
Wen Fang Yang ◽  
Zhen Ya Gu ◽  
Rui Ting Huo
Keyword(s):  
Chemical Vapor Deposition ◽  
Vapor Deposition ◽  
Film Surface ◽  
Chemical Vapor ◽  
Contact Angles ◽  
Water Repellent ◽  
Treatment Technology ◽  
Water Contact ◽  
Lotus Effect ◽  
Pvdf Membrane

Lotus effect is well-known to be governed by chemical properties and nanotextures of the surfaces. In this paper, a method with two-steps treatment technology was applied to develop the superhydrophobic polyvinylidene fruoride(PVDF) membrane with the property of anti-contamination and self-cleaning. First, the PVDF membrane was treated by oxygen plasma so as to get the reactive groups. Second, this film was deposited by perfluoroalkylethyl acrylate precursor/Ar gas via plasma-enhanced chemical vapor deposition (PECVD). The modified film surface exhibited ultra water-repellent ability, showing that the water contact angles was larger than 150 °and the dynamic contact angles was usually lower than 5°.

scholarly journals Fluorosilane Water-Repellent Coating for the Protection of Marble, Wood and Other Materials

Heritage ◽  
2021 ◽  
Vol 4 (4) ◽  
pp. 2668-2675
Author(s):  
Fotios G. Adamopoulos ◽  
Evangelia C. Vouvoudi ◽  
Dimitris S. Achilias ◽  
Ioannis Karapanagiotis
Keyword(s):  
Polymer Networks ◽  
Treated Wood ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Capillary Absorption ◽  
Durability Test ◽  
Water Contact ◽  
Produce Water ◽  
The Aesthetic

The preservation of cultural heritage monuments and artifacts requires the development of methods to produce water-repellent materials, which can offer protection against the effects of atmospheric water. Fluorosilanes are a very promising class of materials, as they act as precursors for the formation of low surface energy polymer networks. 1H,1H,2H,2H-perfluorooctyl-triethoxysilane is applied on marble, wood and the surfaces of other materials, such as glass, silicon wafer, brass, paper and silk. According to the measurements of static water contact angles, it is reported that superhydrophobicity and enhanced hydrophobicity are achieved on the surfaces of coated marble and wood, respectively. Hydrophobicity and hydrophilicity were observed on the treated surfaces of the other materials. More important, water repellency is achieved on any hydrophobic or superhydrophobic surface, as revealed by the very low sliding angles of water drops. The study is accompanied by colorimetric measurements to evaluate the effects of the treatment on the aesthetic appearances of the investigated materials. Finally, the capillary absorption test and a durability test are applied on treated wood and marble, respectively. 

scholarly journals Natural colloid mobilization and leaching in wettable and water repellent soil under saturated condition

2018 ◽  
Vol 66 (3) ◽  
pp. 271-278 ◽  
Author(s):  
Nasrollah Sepehrnia ◽  
Olga Fishkis ◽  
Bernd Huwe ◽  
Jörg Bachmann
Keyword(s):  
Organic Matter ◽  
Colloidal Particles ◽  
Sessile Drop ◽  
Organic Matter Content ◽  
Water Repellency ◽  
Contact Angles ◽  
Matter Content ◽  
Soil Horizon ◽  
Water Repellent ◽  
Coupled Transport

AbstractThe coupled transport of pollutants that are adsorbed to colloidal particles has always been a major topic for environmental sciences due to many unfavorable effects on soils and groundwater. This laboratory column study was conducted under saturated moisture conditions to compare the hydrophobic character of the suspended and mobilized colloids in the percolates released from a wettable subsoil and a water repellent topsoil. Both soils with different organic matter content were analyzed for wettability changes before and after leaching using sessile drop contact angles as well as water and ethanol sorptivity curves, summarized as repellency index. Hydrophobicity of the effluent suspensions was assessed using the C18 adsorption method. Water repellency level of the repellent soil decreased after leaching but remained on a lower level of water repellency, while, the wettable soil remained wettable. The leached colloids from the repellent soil were predominantly hydrophilic and the percentage of the hydrophobic colloid fraction in the effluent did not systematically changed with time. Total colloid release depended on soil carbon stock but not on soil wettability. Our results suggest that due to the respective character of transported colloids a similar co-transport mechanism for pollutants may occur which does not depend explicitly on soil wettability of the releasing horizon, but could be more affected by total SOM content. Further studies with a wider range of soils are necessary to determine if the dominant hydrophilic character of leached colloids is typical. Due to the mostly hydrophilic colloid character we conclude also that changes in wettability status, i.e. of wettable subsoil horizons due to the leachate, may not necessarily occur very fast, even when the overlaying topsoil is a repellent soil horizon with a high organic matter content.

scholarly journals Ultrahydrophobic Textiles Using Nanoparticles: Lotus Approach

2008 ◽  
Vol 3 (4) ◽  
pp. 155892500800300 ◽  
Author(s):  
Karthik Ramaratnam ◽  
Swaminatha K. Iyer ◽  
Mark K. Kinnan ◽  
George Chumanov ◽  
Phillip J. Brown ◽  
...  
Keyword(s):  
Contact Angle ◽  
Water Contact Angle ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Textile Material ◽  
Water Repellent ◽  
Complete Wetting ◽  
Water Contact ◽  
Lotus Effect ◽  
Textile Materials

It is well established that the water wettability of materials is governed by both the chemical composition and the geometrical microstructure of the surface.1 Traditional textile wet processing treatments do indeed rely fundamentally upon complete wetting out of a textile structure to achieve satisfactory performance.2 However, the complexities introduced through the heterogeneous nature of the fiber surfaces, the nature of the fiber composition and the actual construction of the textile material create difficulties in attempting to predict the exact wettability of a particular textile material. For many applications the ability of a finished fabric to exhibit water repellency (in other words low wettability) is essential2 and potential applications of highly water repellent textile materials include rainwear, upholstery, protective clothing, sportswear, and automobile interior fabrics. Recent research indicates that such applications may benefit from a new generation of water repellent materials that make use of the “lotus effect” to provide ultrahydrophobic textile materials.3,4 Ultrahydrophobic surfaces are typically termed as the surfaces that show a water contact angle greater than 150°C with very low contact angle hysteresis.4 In the case of textile materials, the level of hydrophobicity is often determined by measuring the static water contact angle only, since it is difficult to measure the contact angle hysteresis on a textile fabric because of the high levels of roughness inherent in textile structures.

Superhydrophobic and transparent surfaces on cotton fabrics coated with silica nanoparticles for hierarchical roughness

2016 ◽  
Vol 87 (5) ◽  
pp. 552-560 ◽  
Author(s):  
Seon Ah Jeong ◽  
Tae Jin Kang
Keyword(s):  
Silica Nanoparticles ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Cotton Fabrics ◽  
Contact Angles ◽  
Water Repellent ◽  
Textile Fabrics ◽  
Hierarchical Roughness ◽  
Silica Nanomaterials ◽  
Alcohol Solvent

Superhydrophobic and transparent surfaces on cotton fabrics have been developed using silica nanomaterials. Initially, trichlorododecylsilane was treated on the silica nanoparticles to lower the surface energy of the fabric. By simply spraying alcohol suspensions containing hydrophobized silica nanoparticles, extremely water repellent coatings were formed on the textile fabrics. The effect of three types of alcohol solvent on the hydrophobicity of the coated cotton fabrics was examined by measuring the surface wettability. The treated cotton textiles in methanol exhibited contact angles higher than 160°, contact angle hysteresis lower than 10°, and good water repellency. It proved to be essential to form hierarchical morphology in achieving superhydrophobicity.

scholarly journals Influence of organic manure amendments on water repellency, water entry value, and water retention of soil samples from a tropical Ultisol

2016 ◽  
Vol 64 (2) ◽  
pp. 160-166 ◽  
Author(s):  
T.D.P. Liyanage ◽  
D.A.L. Leelamanie
Keyword(s):  
Organic Matter ◽  
Soil Water ◽  
Water Retention ◽  
Water Repellency ◽  
Water Entry ◽  
Contact Angles ◽  
Organic Manure ◽  
Water Repellent ◽  
Water Contact ◽  
In Series

AbstractLowered stability of soil aggregates governed by insufficient organic matter levels has become a major concern in Sri Lanka. Although the use of organic manure with water repellent properties lowers the wetting rates and improves the stability of soil aggregates, its effects on soil hydrophysical properties are still not characterized. Therefore, the objective of this study was to examine the relation of water repellency induced by organic manure amendments to the water entry value and water retention of a Sri Lankan Ultisol. The soil was mixed with ground powders of cattle manure (CM), goat manure (GM),Gliricidia maculata(GL) and hydrophobicCasuarina equisetifolia(CE) leaves to obtain samples ranging from non-repellent to extremely water repellent, in two series. Series I was prepared by mixing GL and CE with soil (5, 10, 25, 50%). Series II consisted of 5% CM, GM, and GL, with (set A) and without (set B) intermixed 2% CE. Water repellency, water entry value, and water retention of samples were determined in the laboratory. Soil-water contact angle increased with increasing organic matter content in all the samples showing positive linear correlations. Although the samples amended with CE showed high soil-water contact angles in series I, set A (without 2% CE) and set B (with 2% CE) in series II did not show a noticeable difference, where >80% of the samples had soil-water contact angles <90°. Water entry value (R2= 0.83–0.92) and the water retention at 150 cm suction (R2= 0.69–0.8) of all the samples increased with increasing soil-water contact angles showing moderate to strong positive linear correlations. However, set A (without 2% CE) and set B (with 2% CE) in series II did not differ noticeably. Water entry value of about 60% the samples was <2.5 cm. Mixing of a small amount (2%) of hydrophobic organic matter with commonly used organic manures slightly increased the water repellency of sample soils, however not up to detrimental levels. It did not generate adverse effects on water entry and increased the water retention. It was clear that intermixing of small quantities of hydrophobic organic manure with organic manures commonly used in Sri Lankan agriculture, would not generate unfavorable impacts on soils.

scholarly journals Superhydrophobicity and Contact-Line Issues

MRS Bulletin ◽  
2008 ◽  
Vol 33 (8) ◽  
pp. 747-751 ◽  
Author(s):  
Lichao Gao ◽  
Alexander Y. Fadeev ◽  
Thomas J. McCarthy
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Water Repellency ◽  
Contact Angles ◽  
Single Step ◽  
Contact Lines ◽  
Lotus Effect ◽  
Three Phase ◽  
Solid Liquid

AbstractThe wettability of several superhydrophobic surfaces that were prepared recently by simple, mostly single-step methods is described and compared with the wettability of surfaces that are less hydrophobic. We explain why two length scales of topography can be important for controlling the hydrophobicity of some surfaces (the lotus effect). Contact-angle hysteresis (difference between the advancing, θA, and receding, θR, contact angles) is discussed and explained, particularly with regard to its contribution to water repellency. Perfect hydrophobicity (θA/θR = 180°/180°) and a method for distinguishing perfectly hydrophobic surfaces from those that are almost perfectly hydrophobic are described and discussed. The Wenzel and Cassie theories, both of which involve analysis of interfacial (solid/liquid) areas and not contact lines, are criticized. Each of these related topics is addressed from the perspective of the three-phase (solid/liquid/vapor) contact line and its dynamics. The energy barriers for movement of the three-phase contact line from one metastable state to another control contact-angle hysteresis and, thus, water repellency.

scholarly journals Facile Method to Prepare Superhydrophobic and Water Repellent Cellulosic Paper

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Ioannis Karapanagiotis ◽  
Diana Grosu ◽  
Dimitra Aslanidou ◽  
Katerina E. Aifantis
Keyword(s):  
Particle Concentration ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Tissue Paper ◽  
Nanoparticle Films ◽  
High Particle ◽  
Aesthetic Appearance ◽  
Static Contact ◽  
Wide Range

Silica nanoparticles (7 nm) were dispersed in solutions of a silane/siloxane mixture. The dispersions were applied, by brush, on four types of paper: (i) modern, unprinted (blank) paper, (ii) modern paper where a text was printed using a common laser jet printer, (iii) a handmade paper sheet detached from an old book, and (iv) Japanese tissue paper. It is shown that superhydrophobicity and water repellency were achieved on the surface of the deposited films, when high particle concentrations were used (≥1% w/v), corresponding to high static (θS≈ 162°) and low tilt (θt< 3°) contact angles. To interpret these results, scanning electron microscopy (SEM) was employed to observe the surface morphologies of the siloxane-nanoparticle films. Static contact angles, measured on surfaces that were prepared from dilute dispersions (particle concentration <1% w/v), increased with particle concentration and attained a maximum value (162°) which corresponds to superhydrophobicity. Increasing further the particle concentration did not have any effect onθS. Colourimetric measurements showed that the superhydrophobic films had negligible effects on the aesthetic appearance of the treated papers. Furthermore, it is shown that the superhydrophobic character of the siloxane-nanoparticle films was stable over a wide range of pH.

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