Air Retention under Water by the Floating Fern <i>Salvinia</i>: The Crucial Role of a Trapped Air Layer as a Pneumatic Spring

Gandyra, Daniel; Walheim, Stefan; Gorb, Stanislav N.; Ditsche, Petra; Barthlott, Wilhelm; Schimmel, Thomas

doi:10.1002/smll.202003425

Cited by 33 publications

(42 citation statements)

References 60 publications

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“…The hydrophilic tip fills the water-air interface and effectively maintains the stability of the air layer. Gandyra et al [138] called this structure "air-spring", which used the trapped air layer to form an elastic spring. When the air layer is impacted by pressure, the force that is subjected to the spring can be ejected from the bubble layer, which greatly improves the stability of the air layer [139] (Figure 11a-c).…”

Section: Physical Methodsmentioning

confidence: 99%

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Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

Feng

Sun

Tian

2021

Adv Materials Inter

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Superhydrophobic surfaces (SHS) for underwater drag reduction draw more and more attention owing to its promising and wide applications such as underwater vehicles, pipeline oil transportation, and aquaculture. However, the drag reduction properties are inextricably linked to the stability of air layer on SHS. This review highlights recent advances regarding SHS for underwater drag reduction in the past three years. First, the fundamental theories are briefly described. Next, the crucial influencing factors, which include dimension and arrangement of particles, layout, and shape of the microstructures, Reynolds number, and attack angle on underwater drag reducing performance of SHS are thoroughly listed. Furthermore, the superior or inferior of these manufacturing techniques is also individually illustrated. After that, the solutions of enhancing stability of the air layer are explicitly classified. Then, the practical applications and its potential value in ships and underwater vehicles, microchannels, as well as fabrics are briefly discussed. Finally, the remaining challenges and promising breakthroughs in the field of SHS for underwater drag reduction are clarified in depth.

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Section: Physical Methodsmentioning

confidence: 99%

“…b) We can calculate a model profile which shows 60% volume fraction of air in the corrugated upper zone.With these data, we can determine the effective air cushion thickness (air spring) to be 2.73 mm for this type of adult (half) leaf of S. molesta. Reproduced with permission [138]. Copyright 2020,Wiley-VCH.…”

mentioning

confidence: 99%

Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

Feng

Sun

Tian

2021

Adv Materials Inter

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“…The excellent air‐retainability of Salvinia structures suggests they could be used long term in drag‐reduction applications. [ 34 ] In addition, several recent studies have confirmed that Salvinia structures reduced drag. For example, natural “eggbeater hairs” reduced drag by up to 30%, [ 77 ] and similar positive results have been obtained in qualitative studies on artificial Salvinia structures.…”

Section: Applications Of Artificial Salvinia Surfacesmentioning

confidence: 96%

“…4) Elastic buffer: the elasticity of the eggbeater structures provides a buffer against the slight deformation of the air–water interface, which helps reduce the interfacial disturbance. [ 34 ] Undercuts or simple inclinations are preconditions for elasticity.…”

Section: Air‐retention Mechanismmentioning

confidence: 99%

Small Structure, Large Effect: Functional Surfaces Inspired by Salvinia Leaves

et al. 2021

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Nature‐inspired superhydrophobic surfaces have attracted significant attention because of their remarkable properties. In particular, recent findings about the aquatic plant Salvinia provide novel approaches for the application of superhydrophobic surfaces. The unique heterogeneous eggbeater structures endow Salvinia leaves with superhydrophobicity and strong adhesion, which ensures that the leaves show durable air‐retainability in underwater environments. However, the complex eggbeater structures present a difficult manufacturing challenge. Therefore, this review first introduces the air‐retention mechanism, which may benefit the design of Salvinia‐inspired structures. Moreover, advanced techniques including photolithography, direct laser lithography, chemical vapor deposition, electrodeposition, electrostatic flocking, 3D printing, chemical etching, and plasma etching recently have been developed for fabricating Salvinia‐inspired structures. This review focuses on the advantages, disadvantages, and application prospects of such techniques. In addition, the excellent air‐retainability of Salvinia structures has inspired many engineering applications, including drag reduction; water harvesting, evaporation, and repellence; oil/water separation; and thermal insulation. This review discusses the performance and challenges of artificial structures to such applications. Finally, methods of evaluating air‐retainability are discussed. It is expected that this review will not only satisfy scientific curiosity but also contribute to the design and application of Salvinia‐inspired functional surfaces.

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“…Therefore, the EU project AIRCOAT 1 aims at reducing hull friction to a minimum. In water ferns, the Salvinia effect of a micro-and nanostructured surface with hydrophobic and hydrophilic characteristics allows for air retention under water [1] and while the air spring effect contributes to the air layer stability [6]. Inspired by the Salvinia effect, the AIRCOAT project intends to develop a biomimetic passive air layer technology.…”

Section: Introductionmentioning

confidence: 99%

Validation of a Flow Channel to Investigate Velocity Profiles of Friction-Reducing Ship Coatings

Weisheit¹,

Schneider²,

Serr³

et al. 2021

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Reducing friction with specialised hull coatings or air lubrication technologies has a potential reducing energy consumption and emissions in shipping. The EU project AIRCOAT combines both by developing a passive air lubrication technology inspired by nature that is implemented on a self-adhesive foil system. Besides validating the friction reduction it is of high interest to understand the underlying mechanism that causes the reduction. Therefore, a flow channel was designed, that creates a stationary turbulent flow within a square duct allowing for non-invasive measurements by laser doppler velocimetry. The high spatial resolution of the laser device makes recording velocity profiles within the boundary layer down to the viscous sublayer possible. Determination of the wall shear stress τ enables direct comparison of different friction reduction experiments. In this paper we validate the methodology by determining the velocity profile of the flat channel wall (without coatings). We further use the results to validate a CFD model in created in OpenFOAM. We find that velocities along the longitudinal axis are generally in good agreement between numerical and experimental investigations.

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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

Cited by 33 publications

References 60 publications

Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

Recent Developments of Superhydrophobic Surfaces (SHS) for Underwater Drag Reduction Opportunities and Challenges

Small Structure, Large Effect: Functional Surfaces Inspired by Salvinia Leaves

Validation of a Flow Channel to Investigate Velocity Profiles of Friction-Reducing Ship Coatings

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