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![Lotus leaf: (a) Magnification of one. From website [14]; (b) Three different magnification of SEM images showing morphological micro-and nanostructures. From Koch et al. [13].](profile/Mohamed_Gad-El-Hak/publication/257672827/figure/fig1/AS:738894500859905@1553177585199/Lotus-leaf-a-Magnification-of-one-From-website-14-b-Three-different.jpg)
Lotus leaf: (a) Magnification of one. From website [14]; (b) Three different magnification of SEM images showing morphological micro-and nanostructures. From Koch et al. [13].
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![Fig. 1. Lotus leaf: (a) Magnification of one. From website [14]; (b)...](profile/Mohamed_Gad-El-Hak/publication/257672827/figure/fig1/AS:738894500859905@1553177585199/Lotus-leaf-a-Magnification-of-one-From-website-14-b-Three-different_Q320.jpg)
In this review we discuss the current state of the art in evaluating the fabrication and performance of biomimetic superhydrophobic materials and their applications in engineering sciences. Superhydrophobicity, often referred to as the lotus effect, could be utilized to design surfaces with minimal skin-friction drag for applications such as self-c...
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... characteristics of 200 species. They demonstrated that the epidermal (i.e. outermost) cells of the lotus leaves form papillae, which act as microstructure roughness. The papillae are superimposed by a very dense layer of epicuticular waxes (wax crystals), also referred to as hair-like structures [12] or nanostructure roughness [13]. Fig. 1 shows different degrees of magnification of lotus leaves using SEM images from one to 10 6 times. Epicuticular waxes themselves have hydrophobic properties, which together with micro-and nanostructure roughness, result in reduced contact area between water droplets and the leaf's surface. This combination results in static contact ...
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... structure is studied by Choi and Kim [42]. These authors present slip length of their surface in comparison to that of a smooth one. Lee and Kim [4] demonstrated that the slip length can be maximized by superimposing a nanostructure onto a microfabricated structure, similar to the case of wax crystals on papillae of the lotus leaves as shown in Fig. 10. These authors demonstrated that the contact angle for their surfaces can approach 180 • . In addition, they showed that the slip length can be increased up to 400 ...
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... are limitations for commercializing microfabricated surfaces such as those shown in Figs. 8-10. Production cost is probably the most prohibitive issue with microfabricated surfaces. Recent studies, however, have shown that there are alternative methods for engineering superhydrophobic surfaces more cost-effectively. As discussed by Emami et al. [5], one can produce a superhydrophobic surface by randomly depositing hydrophobic ...
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... issue with microfabricated surfaces. Recent studies, however, have shown that there are alternative methods for engineering superhydrophobic surfaces more cost-effectively. As discussed by Emami et al. [5], one can produce a superhydrophobic surface by randomly depositing hydrophobic particles (e.g. aerogel) on a substrate (see also [6,7]). Fig. 11(a) shows an SEM image of aerogel powders synthesized using sodium silicate and deposited on a substrate. The static contact angle is measured for a coated surface with aerogel powders to show its superhydrophobicity. Fig. 11(b) shows that the contact angle for such a surface is 150 • ...
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... a superhydrophobic surface by randomly depositing hydrophobic particles (e.g. aerogel) on a substrate (see also [6,7]). Fig. 11(a) shows an SEM image of aerogel powders synthesized using sodium silicate and deposited on a substrate. The static contact angle is measured for a coated surface with aerogel powders to show its superhydrophobicity. Fig. 11(b) shows that the contact angle for such a surface is 150 • ...
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... roughness (posts or particles) and compare their results with those of surfaces manufactured via microfabrication. Their numerical simulations indicated that the gas fraction has a significant impact on the characteristics of a superhydrophobic surface, as it affects the slip length and therefore the skin-friction coefficient. As can be seen in Fig. 12, the friction coefficient decreases with increasing gas fraction for surfaces with staggered posts and randomly distributed posts. In addition, the difference between the skin-friction coefficient of the random posts and that of the staggered posts increases by increasing the gas fraction. Thus, the surface with randomly distributed ...
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... orientation of the fibers is the result of the inherent electrostatic instability of the charged jet as it travels from the spinneret to the collector. This instability can be reduced by using a DC-biased AC potential that induces short segments of alternating polarity, thereby reducing the magnitude of the destabilizing force on the fiber (see Fig. 14(a)) [43]. Fig. 14 shows SEM images of fiber mats produced via DC-electrospinning and DC-biased AC-electrospinning. As shown in Fig. 14, DC-biased AC-electrospinning provides a better control over the microstructure of deposited fibrous mats. The insert in Fig. 14(b) shows a water droplet on the coating with a static contact angle of 157 ...
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... fibers is the result of the inherent electrostatic instability of the charged jet as it travels from the spinneret to the collector. This instability can be reduced by using a DC-biased AC potential that induces short segments of alternating polarity, thereby reducing the magnitude of the destabilizing force on the fiber (see Fig. 14(a)) [43]. Fig. 14 shows SEM images of fiber mats produced via DC-electrospinning and DC-biased AC-electrospinning. As shown in Fig. 14, DC-biased AC-electrospinning provides a better control over the microstructure of deposited fibrous mats. The insert in Fig. 14(b) shows a water droplet on the coating with a static contact angle of 157 degrees, proving ...
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... to the collector. This instability can be reduced by using a DC-biased AC potential that induces short segments of alternating polarity, thereby reducing the magnitude of the destabilizing force on the fiber (see Fig. 14(a)) [43]. Fig. 14 shows SEM images of fiber mats produced via DC-electrospinning and DC-biased AC-electrospinning. As shown in Fig. 14, DC-biased AC-electrospinning provides a better control over the microstructure of deposited fibrous mats. The insert in Fig. 14(b) shows a water droplet on the coating with a static contact angle of 157 degrees, proving superhydrophobicity even in the case of random fiber deposit [11]. This is because, similar to the case of ...
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... thereby reducing the magnitude of the destabilizing force on the fiber (see Fig. 14(a)) [43]. Fig. 14 shows SEM images of fiber mats produced via DC-electrospinning and DC-biased AC-electrospinning. As shown in Fig. 14, DC-biased AC-electrospinning provides a better control over the microstructure of deposited fibrous mats. The insert in Fig. 14(b) shows a water droplet on the coating with a static contact angle of 157 degrees, proving superhydrophobicity even in the case of random fiber deposit [11]. This is because, similar to the case of microfabricated surfaces, such superhydrophobic fibrous coatings can provide the porosity that is necessary to entrap air when the surface is ...
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... the slip length results attained using this fabrication approach are comparable to those obtained using ordered micro/nanostructure surfaces [4]. It is worth mentioning that the morphology of the fibers influences the hydrophobicity of the surface. For example, fiber diameter can affect the static contact angle of the coating, as shown in Fig. 15. This figure shows that contact angle decreases with increasing fiber diameter. However, one should note that since other microstructural parameters of the surfaces reported in this figure were not kept constant while fiber diameter was varied, changes in the fiber diameter could have affected the porosity of the mat. Therefore, in the ...
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... striders, Gerris remigis, possess a very rare trait that allows them to walk on water. Water striders owe this ability to the hydrophobic waxy microhairs covering their legs, microsetae, which are superimposed with nanogrooves [2] as shown in Fig. ...
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... the volume of the displaced water caused by immersing a single leg is 300 times that of the leg itself. Feng et al. [45] have modeled the ultra-hydrophobicity of a water strider's leg by providing a theoretical analysis, coupled with experimental measurements, to determine how deep the leg can reach before piercing the water surface as shown in Fig. 17. They demonstrated that the maximum depth, h max , depends on the diameter, D, and the contact angle of the leg, φ leg . Their results are shown in Fig. 18. It can be seen that for the actual diameter range (140-180 μm) and for the measured maximum depth (h max = 4.38 ± 0.02 mm), the contact angle should be at least 168 • , i.e. highly ...
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... of a water strider's leg by providing a theoretical analysis, coupled with experimental measurements, to determine how deep the leg can reach before piercing the water surface as shown in Fig. 17. They demonstrated that the maximum depth, h max , depends on the diameter, D, and the contact angle of the leg, φ leg . Their results are shown in Fig. 18. It can be seen that for the actual diameter range (140-180 μm) and for the measured maximum depth (h max = 4.38 ± 0.02 mm), the contact angle should be at least 168 • , i.e. highly water-repellent. Such a high contact angle allows water striders to stand on water, even in the presence of rain or water ...
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... and the maximum pitch for superhydrophobic surfaces made up of randomly distributed posts. This information is used in Eq. (2) to determine the maximum allowable hydrostatic pressure, which corresponds to the post that has the maximum local gas fraction. In a Voronoi diagram, the superhydrophobic surface is divided into cells, as shown in Fig. 19. Each post has a single surrounding Voronoi cell consisting of all points on the surface that are closer to that post than to any other post. The sides of a Voronoi cell are the locations of the points on the surface that are equidistant from the two nearest posts. The Voronoi nodes are the points equidistant from three (or more) ...
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... Fig. 20. It can be seen that the maximum allowable pressure decreases dramatically when the posts are arranged randomly. The results of this figure indicate that superhydrophobic surfaces with random roughness are more susceptible to failure under hydrostatic pressures. Therefore, although random posts can result in a better drag reduction (see Fig. 12), they are more likely to fail under elevated ...
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... particles in comparison to the ordered distributed ones. These authors also conducted a series of 3-D full-morphology (FM) numerical simulations and analytical expressions to predict the critical pressure (pressure beyond which the surface departs from the Cassie state) against solid volume fraction of their granular porous coatings, as shown in Fig. 21. This figure shows that the air-water interface can sustain more pressure as the solid volume fraction increases. Moreover, the surface with random particles is more susceptible to failure under hydrostatic pressure, as ...
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Nickel (Ni) films with positive and negative textured surfaces of lotus and rice leaf patterns were fabricated through an inexpensive and effective method. The as-prepared Ni films were superhydrophobic and exhibited excellent tribological properties after chemical treatment. Experimental results indicated that the water contact angles (WCAs) on th...
Previous studies on submerged superhydrophobic surfaces focused on performance variables such as drag reduction and longevity. However, to use such surfaces for practical applications, environmental factors such as water salinity must be investigated and understood. In this work, experiments were carried out to investigate the impact of salt (sodiu...
![Figure 3. (a) Water strider standing on water; from website [39]. (b)...](publication/272660164/figure/fig1/AS:676538160775180@1538310675775/a-Water-strider-standing-on-water-from-website-39-b-SEM-image-of-water-striders_Q320.jpg)
We review recent developments in nature-inspired superhydrophobic and omniphobic surfaces. Water droplets beading on a surface at significantly high static contact angles and low contact-angle hystereses characterize superhydrophobicity. Microscopically, rough hydrophobic surfaces could entrap air in their pores resulting in a portion of a submerge...
Citations
... This is due to surface tension, which keeps a tiny layer of air between the solid surface and the liquid. As water droplets roll off these surfaces, they carry away dirt, and this is known as the lotus effect, or self-cleaning [6][7][8]. Numerous studies have been carried out over the last few decades to look at the concepts, architectures, and workings of these self-cleaning surfaces [9,10]. The waxy substance or chemicals and the tiny bumps on the surface of the lotus leaf make it extremely hydrophobic. ...
This review study provides an overview of superhydrophobic surface fabrication techniques based on laser surface texturing that are environmentally friendly. There are many prospective applications for superhydrophobic surfaces, including self-cleaning, anti-icing, oil–water separation, anti-corrosion, and anti-biofouling. Except for hydrophobic nanoparticle coating procedures, superhydrophobic surface manufacturing methods have not been sufficiently developed or commercialized. Among the various fabrication techniques, laser surface texturing is an important process that is different from superhydrophobic surface coating processes. This technique can be used to fabricate superhydrophobic surfaces in an eco-friendly manner and can process selected regions without the use of a mask. This review study is intended to improve our understanding of these laser surface texturing technologies for fabricating superhydrophobic surfaces and to open up new research areas. In this review, procedures, materials, and parameters for creating superhydrophobic surfaces using laser processing and environmentally friendly post-processing are analyzed and summarized. Because they involve the use of hazardous chemicals, common laser processes with fluorination or silanization coatings were not included. Finally, we provide an overview of the study trends and offer conclusions based on this review.
... Currently, in addition to adding chemical components to the substrate metal to improve its stability, improving the water resistance of the substrate surface, when combined with coating technology, has been a hot topic in the research field [16][17][18][19]. Some studies have reported that superhydrophobic surfaces can greatly improve the overall performance of the surface, such as corrosion resistance, stain resistance, and self-cleaning [20][21][22][23][24]. The most famous functional phenomenon of superhydrophobic surfaces is the self-cleaning effect of "lotus leaves". ...
In order to improve the anti-fouling of stainless steel surfaces in outdoor or humid environments, a superhydrophobic modification is often used to improve its self-cleaning performance. However, the mechanical stability of superhydrophobic surfaces remains a challenge. In this paper, a two-step preparation method was adopted to prepare the micro–nanocomposite coating, which innovatively combined “top-down” and “bottom-up” approaches, and also coupled together two key factors that affect superhydrophobicity: a rough microstructure, and low surface energy. The silver mirror, adhesion, and pollution-resistance results show that the composite coating samples, which were obtained by optimizing the preparation process, have excellent water repellency and self-cleaning properties. Meanwhile, the samples demonstrate outstanding mechanical stability, and can resist damage from sandpaper and tape. The two-step preparation method was simple, fast, and efficient. This method could be popularized and applied to the preparation of superhydrophobic surfaces on metal substrates.
... In recent decades, superhydrophobic surfaces (SHSs) have garnered significant attention, particularly with the rapid development of structure visualization and microfabrication/ nanofabrication technology [1]. These surfaces, inspired by the inherent superhydrophobicity observed in nature, such as on lotus leaves [2] and water striders [3], exhibit extremely high contact angles and low contact angle hysteresis. They offer numerous applications, including self-cleaning [4], drag reduction [5], antifogging [6,7], oil-water separation [8,9], and anti-icing [10]. ...
Superhydrophobic surfaces (SHSs) have received significant attention due to their low surface energy, which facilitates droplet dewetting transition and promotes jumping condensation. However, at high subcooling temperatures, SHSs encounter challenges in maintaining their performance. They are prone to issues like nucleation-induced flooding condensation and reduced hydrophobicity. To address the limitations of SHSs at high subcooling temperatures, we propose the concept of superhydrophobic lubricant-infused surfaces (LISs). These combine the advantages of superhydrophobicity with enhanced functionality provided by a lubricant layer. Firstly, the wetting and adhesion of droplets on LISs have been explored, considering the effects of substrate characteristic and lubricant thickness. Subsequently, the surface condensation on both LISs and SHSs at high subcooling temperatures has been investigated. The failure modes of SHSs at high subcooling temperatures have been revealed. Our molecular dynamics simulations demonstrate that by infusing a superhydrophobic lubricant, the LISs can effectively overcome the limitations of SHSs. This enables the maintenance of dewetting property and ensures droplet jumping condensation, even at high subcooling temperatures. Finally, a comprehensive map is developed to compare the static wettability and dynamic wettability during condensation under different substrate characteristics and lubricant thicknesses. The present work can provide valuable insights into the potential of LISs in addressing the limitations of SHSs. It paves the way for applications in various fields, such as self-cleaning, anti-icing, moisture resistance, drag reduction, and enhanced heat transfer performance.
... i) By modifying a lower surface energy substance on a rough surface ii) By increasing the roughness of the surface of the low surface energy substance [6,7] Modifying a surface with low surface energy groups can effectively increase its water as well as oil contact angles and roughening is another methodology to enhance the wettability of a surface. Xiaolong et.al put forth that superamphiphobicity can be approached in one step with Multiwalled carbon Nanotube with a coralline structure [8]. ...
The word superamphiphobicity refers to the effect in which the techniques of surface chemistry and surface-roughness in order to make the surface superhydrophobic and superleophobic, both sharing the criteria of contact angle greater than 150 0 along with lower contact angle hysteresis. In this review, we have recapitulated the modification of the surface, selection of substrates and fabrication methods that lead to superamphiphobicity and their characters that lead to functional applications. 1. Introduction: Extensive research interest has been observed in the field of superamphiphobic surfaces that are man-made. In a wider view nature provides us a variety of plant leaves, insect legs, and wings that are superamphiphobic. Contact angles larger than 150 0 and sliding angles less than 10 0 formulate the concoction of superamphiphobic coatings. Superamphiphobicity provides excellent outcomes in self-cleaning, anti-fouling, anti-bacterial, gas sensing, oil or water separation and droplet manipulation properties [1]. Wettability of a solid surface is determined by two factors, nature and its structure. Previous studies have found that constructing appropriate hydrophilic regions on superamphiphobic surfaces would promote nucleation and self-repelled jumping has become an important way to remove water droplets from the surface [2]. There are two major approaches to construct superhydrophobic surfaces over a solid surface [3-5]. i) By modifying a lower surface energy substance on a rough surface ii) By increasing the roughness of the surface of the low surface energy substance[6, 7] Modifying a surface with low surface energy groups can effectively increase its water as well as oil contact angles and roughening is another methodology to enhance the wettability of a surface. Xiaolong et.al put forth that superamphiphobicity can be approached in one step with Multiwalled carbon Nanotube with a coralline structure [8]. The terminologies superomniphobic and superamphiphobic were used to describe the nature of these surfaces both superhydrophobic and superoleophobic. Superleophobic surfaces were achieved by introducing a third factor, re−entrant curvature structure and it also resembles a overhanging structure reported by Cohen et.al and Gao .et.al respectively [9, 10] whereas the cooperation of micro or nano scale heirarchial structures with low surface energy materials has been the most important strategy for fabricating superhydrophobic surfaces [11].
... Numerical studies are conducted both on hydrophobic [39,134,136,137,[140][141][142] and hydrophilic [143,144] surfaces. For particular cases of super-hydrophilic and super-hydrophobic surfaces, analytical solutions were obtained [145], which play an important role in terms of describing the physics of the process and in the transition to large-scale multiparameter models inherent in a wide class of practical applications (antibacterial/anti-biofouling [146,147], oil recovery [148,149], drag reduction [150,151], anti-corrosion [152,153], self-cleaning [154,155], anti-icing and anti-fogging [156,157], and a combination of both for pool boiling [158,159], oil-water separators [38], lubrication [38], heat pipe wicks [38], dental implants [38], water splitting for environmentally friendly H 2 O 2 [38] and microfluidics [160]), and natural phenomena (lotus leaves [161], rose petals [162], water ferns [163,164], Sphagnum moss [163,164], water striders [165], butterfly wings [166], etc.). The importance of the problem of heating and evaporation of sessile drops is well known and widely described [39]. ...
The processes of interaction of liquid droplets with solid surfaces have become of interest to many researchers. The achievements of world science should be used for the development of technologies for spray cooling, metal hardening, inkjet printing, anti-icing surfaces, fire extinguishing, fuel spraying, etc. Collisions of drops with surfaces significantly affect the conditions and characteristics of heat transfer. One of the main areas of research into the interaction of drops with solid surfaces is the modification of the latter. Changes in the hydrophilic and hydrophobic properties of surfaces give the materials various functional properties—increased heat transfer, resistance to corrosion and biofouling, anti-icing, etc. This review paper describes methods for obtaining hydrophilic and hydrophobic surfaces. The features of the interaction of liquid droplets with such surfaces are considered. The existing and possible applications of modified surfaces are discussed, as well as topical areas of research.
... In the lotus leaf effect, the static contact angle between the lotus leaf surface and water is more than 150 • , while the water sliding angle is only 1.9 • . The water droplets attached to the surface of the lotus leaf can easily slide down and 2 of 19 take away the pollutant particles on the surface, resulting in a self-cleaning effect [47,48]. Superhydrophobic surfaces in a static self-wetting state in nature provide an important reference for the construction of biomimetic wood superhydrophobic coatings [49][50][51]. ...
As the focus of architecture, furniture, and other fields, wood has attracted extensive attention for its many advantages, such as environmental friendliness and excellent mechanical properties. Inspired by the wetting model of natural lotus leaves, researchers prepared superhydrophobic coatings with strong mechanical properties and good durability on the modified wood surface. The prepared superhydrophobic coating has achieved functions such as oil-water separation and self-cleaning. At present, some methods such as the sol-gel method, the etching method, graft copolymerization, and the layer-by-layer self-assembly method can be used to prepare superhydrophobic surfaces, which are widely used in biology, the textile industry, national defense, the military industry, and many other fields. However, most methods for preparing superhydrophobic coatings on wood surfaces are limited by reaction conditions and process control, with low coating preparation efficiency and insufficiently fine nanostructures. The sol-gel process is suitable for large-scale industrial production due to its simple preparation method, easy process control, and low cost. In this paper, the research progress on wood superhydrophobic coatings is summarized. Taking the sol-gel method with silicide as an example, the preparation methods of superhydrophobic coatings on wood surfaces under different acid-base catalysis processes are discussed in detail. The latest progress in the preparation of superhydrophobic coatings by the sol-gel method at home and abroad is reviewed, and the future development of superhydrophobic surfaces is prospected.
... The concept of superhydrophobicity was inspired by nature, with a WCA of more than 150°a nd a sliding angle below 10°to reduce the slippery and sticky properties of the surface against water. [52][53][54][55][56] Superhydrophobic surfaces, such as lotus leaves, 57,58 butterfly wings, 59,60 peanut leaf, 61 red rose petal, 62,63 water strider legs, 64 and fish scale, 65,66 have low surface energy to resist wetting. Tables 1 and 2 provide various examples of nature-inspired flora and fauna, as well as their mechanisms which help to understand the superhydrophobic concept from nature and inspire engineers to use concepts of superhydrophobicity to prevent biofouling for engineering applications. ...
Biofouling is a major issue for many industries including shipping, oil, and gas and can lead to accelerated corrosion, particularly for structures and components in and around salt water. Many efforts are undertaken to lessen its impact and financial losses. One of the promising methodologies is application of antibiofouling coatings to minimize biofouling, and the best results were observed with a superhydrophobic coating. Ample literature reviews on superhydrophobic coating have shown biofouling inhibition on the surface due to high wetting angles similar to the phenomenon on a lotus leaf. The hydrophobic coating can be deposited using multiple techniques such as electroless plating, chemical vapor deposition (CVD), sol–gel, and electrodeposition. In this review, an effort has been made to encompass such experimental work under a single domain and compare the effectiveness of each coating. In addition, mechanical properties and surface characteristics such as wetting angle, surface energy, and morphology were also discussed for various types of polymeric coating. Similarly, the application of nanoparticles such as ZnO, SiO2, TiO2, and CeO2 was found to improve the substrate's mechanical properties, the durability of coatings, improvement in wear properties, adhesion, interlaminar cohesion, and increased wetting angle and above all, improve superhydrophobicity. These improvements are compared for various nanoparticle integrated coatings. In addition, other novel approaches to prevent marine biofouling by various polymer-based coatings such as superhydrophobic, foul-release, and foul-resistant coatings are discussed in this paper.
... Thus, it can be concluded that the studied SAILs work just as effectively no matter the side of the leaf. Also, analyzing the results presented in Fig. 5, a crucial side to the wettability issue is the variation between surfaces, i.e., waxy cuticle, surface roughness [10], or another part of the morphological structure of the leaf [54][55][56][57][58][59]. Furthermore, CA values of the surfaces analyzed were observed to increase cornflower < winter rapeseed < white mustard < paraffin (exceptions were for winter rapeseed wetted by SAIL-4 and for white mustard wetted by SAIL-3). ...
... From an application point of view, low CA values result in better distribution of droplets over the leaf surface, which finally affects the agrochemical delivery process. However, as an aside, it is worth noting that in the literature, usually 90 • CA is treated as a threshold value, which unambiguously allows estimating the degree of wetting of the tested surfaces [54,55,57]. In addition, the individual CA values depended on the structure of the SAILs themselves, as each of the compounds studied contains at least one long alkyl substituent in the cation. ...
... The drag forces on the walls of confined flows can reduce the fluid flow's momentum, which leads to a reduction in efficiency of the designed system. The most practical approach used to achieve the overall viscous shear drag reduction (DR) is the passive technique (e.g., changing the wall topology) [11][12][13]. The slip over the SH coating surface could be explained as a combination of direct and indirect effects. ...
... Thus, the slip length values in the laminar region are lower than those in turbulent flow regions. When the Reynolds number is high, shear stress and pressure fluctuation are caused by turbulence enhancing the wetting [13], which is an indirect effect. By modelling the air diffusion process of a plastron as a nonlinear oscillation system, Piao and Park [14] investigated the effects of fluctuating air-water interfaces. ...
... Few studies were performed to investigate the air plastron layer as it was subjected to the flow. Most of them were carried out in a water tunnel using TIR and high-speed camera techniques for optical observations [13,20,21] or tracer-based methods such as particle image velocimetry (PIV) technique [22]. It is challenging to visualize the plastron in large-scale flow facilities in turbulent flows. ...
Drag reduction (DR) using superhydrophobic surfaces (SHSs) has received intensive interest due to the emergence of SH coating technology. The air layer (plastron “δ”) trapped between the SHS and the water controls the flow slip over the SHSs. We demonstrate slippage over three fabricated SHSs in laminar and low turbulent Taylor–Couette flows. We experimentally investigate how the slip length increases with a higher Reynolds number (Re) over the tested SHSs; simultaneously, the air plastron thickness investigates using a viscous model. The mean skin friction coefficient (Cf) can be fitted to a modified semi-empirical logarithmic law expressed in the Prandtl–von Kármán coordinate. An effective slip length is estimated in the 35–41 µm range with an achieved 7–11% DR for the tested surfaces. Statistical analysis is used to develop a regression model from the experimental data. The model shows an R2 of 0.87 and good agreement with the experimental data. This shows the relation between the dimensionless slip length (b+), the dimensionless plastron thickness (δ+), and the Reynolds number, which is directly proportional. The regression model shows that b+ and Reynolds numbers have a higher impact on the δ+ than the surface wettability, which attribute to the small difference in the wetting degree between the three tested surfaces. The practical importance of the work lies in its ability to provide a deep understanding of the reduction in viscous drag in numerous industrial applications. Furthermore, this research serves as a groundwork for future studies on hydrophobic applications in internal flows.
... Με βάση τα προαναφερθέντα, η υπερυδροφοβικότητα που παρατηρήθηκε στον λωτό χρησιμοποιείται για τον σχεδιασμό επιφανειών με ελάχιστη αντίσταση τριβής των επιφανειών, για εφαρμογές όπως ο αυτοκαθαρισμός και η εξοικονόμηση ενέργειας. Στο πλαίσιο αυτό παρουσιάζεται η κατασκευή υπερυδρόφοβων επιφανειών με διατεταγμένες και διαταραγμένες μικροδομές σε υποβρύχια επιτρέποντας τον "διασκελισμό" σε νερό και τη μελέτη της μακροζωίας των βυθισμένων υπερυδρόφοβων επιφανειών για υποβρύχιες εφαρμογές, για την κατασκευή υπερυδρόφοβου χαρτιού και καλυμμάτων καθώς και για τη νανοσυσκευασία (Hu et al. 2010, Yang & Deng 2008, Samaha et al. 2011, Samaha et al. 2012, Wy et al. 2021, Xiu et al. 2021), ...
Η περί τη βιομιμητική (Biomimetic) έρευνα αντλεί έμπνευση από ιδιότητες ζωντανών οργανισμών που υπάρχουν στη φύση και ζουν σε διαφορετικούς βιοτόπους και διακριτά ενδιαιτήματα. Η βιομιμητική βασίζεται στη μελέτη, την
ανάδειξη, την αντιγραφή και την προσομοίωση ιδιοτήτων και δομικών
χαρακτηριστικών έμβιων οργανισμών που έχουν αποδεδειγμένα αντέξει περιβαλλοντικές καταπονήσεις. Έτσι, δομές και ιδιότητες ζωντανών οργανισμών (υδρόφοβες, οπτικές και άλλες ιδιότητες) που αποκαλύπτονται με τη βασική έρευνα χρησιμοποιούνται από την τεχνολογία δημιουργώντας ανταλλακτικές αξίες, θέσεις εργασίας, χρηστικά και πρωτοποριακά προϊόντα.
Η βιομίμηση (Biomimicry) έχει σχέση με την απατηλή μίμηση χαρακτηριστικών ενός οργανισμού από έναν άλλο οργανισμό για ξεγέλασμα, για προσέλκυση ή άμυνα. Για παράδειγμα, τα άνθη ορισμένων φυτών όπως οι ορχιδέες μιμούνται, καθώς ανοίγουν και επιδεικνύουν τον φαινότυπό τους (χρώματα, σχήματα και
συμμετρίες) όσον αφορά τη μορφολογία, ορισμένα έντομα για να τα προσελκύσουν. Επίσης, πεταλούδες και έντομα μιμούνται το φύλλωμα δέντρων
και θάμνων για να μην γίνουν αντιληπτές/αντιληπτά από θηρευτές. Τόσο η βιομιμητική όσο και η βιομίμηση σχετίζονται με την αποκάλυψη χαρακτηριστικών ιδιοτήτων της ύλης της φύσης από την ερευνητική δραστηριότητα των ανθρώπων. Ωστόσο, η ανάπτυξη των ηλεκτρονικών μικροσκοπίων ήταν μια κομβική υποδομή αναφοράς για τη βασική έρευνα που πυροδότησε πολλές από τις ιδέες της βιοέμπνευσης και των μετέπειτα εφαρμογών. Κατά συνέπεια, στη βιομιμητική
τεχνική καθρεφτίζονται επιλεκτικά ιδιότητες της ύλης της φύσης που προβάλλονται με προσομοίωση σε τεχνητές, ανθρώπινες κατασκευές.
Η πρωταρχική προσέγγιση θεμάτων βιομιμητικής (Biomimetics) συνδέεται
με την άποψη ότι οργανισμοί που ζουν σε βιοτόπους έχουν ήδη αποκριθεί με επιτυχία σε περιβαλλοντικές καταπονήσεις, με την πάροδο του χρόνου και πρόκειται για εκατομμύρια χρόνια εξέλιξης και προσαρμογής. Δηλαδή, η επιβίωση και η ανάπτυξή τους έχει αποδεδειγμένα δοκιμαστεί και βασίζεται στις προσαρμογές τους στο φυσικό τους περιβάλλον. Η βιομιμητική μελετά και αναζητά τις επιτυχημένες αποκρίσεις στο περιβάλλον από τους ζωντανούς οργανισμούς, με απώτερο στόχο να προτείνει λύσεις, έτσι ώστε επιλεγμένα αντικείμενα, υλικά και δομές που θα βοηθήσουν την ανθρώπινη και ανθρωποκεντρική δραστηριότητα να
βρίσκονται σε δυναμική ισορροπία με το περιβάλλον του πλανήτη μας.
Στις μέρες μας είναι γεγονός ότι από επίμονες, επίπονες και μακρόχρονες μελέτες φυσικής ιστορίας, οραματισμό και έμπνευση προκύπτουν σύγχρονες τεχνολογικές εφαρμογές και νέα προϊόντα με ποικίλες εφαρμογές. Η ανάδειξη της σημασίας της βιομιμητικής, της βιομίμησης, της βιομιμητικότητας ή του βιομιμητισμού σχετίζεται με τη συμβολή την οποία μπορεί να προσφέρει η ενσωμάτωση “πληροφορίας” που
προϋπήρχε και προϋπάρχει στη φύση σε καινοτομίες και ανθρωπογενείς επεμβάσεις στο περιβάλλον, με στόχο τη βιώσιμη ανάπτυξη. Στο πλαίσιο αυτό ενθαρρύνεται η διεπιστημονικότητα, η αλληλεπίδραση ιδεών και καινοτόμων απόψεων. Πρόκειται για ταχύτατα αναπτυσσόμενες διεργασίες διεθνώς, σε πανεπιστήμια και ερευνητικές δομές. Με εφόδιο το έργο που διεξάγεται και δημοσιοποιείται, θετικές επιστήμες, κοσμετολογία, αθλητισμός, φαρμακευτική, γεωπονία, αρχιτεκτονική, αρχαιολογία, καλές τέχνες, επιστήμες υλικών, κατασκευών, υφασμάτων, υγείας, περιβάλλοντος και διαστήματος, επιστήμες
αγωγής και φυσικής αγωγής αποβλέπουν σε ανάλογα αποτελέσματα.
Η έμβια ύλη της φύσης, η οποία αποτελεί “καλούπι” για την τεχνολογία. Επίσης, προσεγγίζονται με παιδεία νέες πτυχές έρευνας και τεχνολογικών δυνατοτήτων. προκλήσεων και προοπτικών για τις επερχόμενες γενιές. Εννοείται ότι τα κεφάλαια του παρόντος συγγράμματος δεν καλύπτουν όλη την έκταση της βιομιμητικής και της βιομίμησης, αλλά είναι ένα πρώτο, σημαντικό βήμα για την ανάδειξη του θέματος και της έμπνευσης καθώς και την προώθηση των ερεθισμάτων ή των παρατηρήσεων από την έμβια ύλη της φύσης.
