Effects of hydrostatic pressure on the drag reduction of submerged aerogel-particle coatings

Samaha, Mohamed A.; Tafreshi, H. Vahedi; Gad‐el‐Hak, Mohamed

doi:10.1016/j.colsurfa.2012.02.025

Cited by 33 publications

(25 citation statements)

References 39 publications

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“…18,[24][25][26] Other studies have been performed to determine the meniscus shape at different pressures up to the critical pressure. [27][28][29] Samaha et al 17 experimentally determined the so-called "terminal pressure" beyond which the surface undergoes a global transition from the Cassie state to the Wenzel state, and therefore can no longer generate drag reduction. Note that the terminal pressure differs from the critical pressure.…”

Section: Introductionmentioning

confidence: 99%

“…Large-scale manufacturing of microfabricated superhydrophobic surfaces is prohibitively expensive. An alternative solution to circumvent the high cost is to produce surfaces made up of random deposition of hydrophobic particles [16][17][18] or electrospun fibers. 19,20 Electrospinning of superhydrophobic polymers is a simple, low-cost method that could be used to deposit micro-to nanofibrous coatings onto substrates of arbitrary geometry.…”

Section: Introductionmentioning

confidence: 99%

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Sustainability of superhydrophobicity under pressure

2012

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Prior studies have demonstrated that superhydrophobicity of submerged surfaces is influenced by hydrostatic pressure and other environmental effects. Sustainability of a superhydrophobic surface could be characterized by both how long it maintains the trapped air in its surface pores, so-called “longevity,” and the pressure beyond which it undergoes a global wetting transition, so-called “terminal pressure.” In this work, we investigate the effects of pressure on the performance of electrospun polystyrene fibrous coatings. The time-dependent hydrophobicity of the submerged coating in a pressure vessel is optically measured under elevated pressures. Rheological studies are also performed to determine the effects of pressure on drag reduction and slip length. The measurements indicate that surface longevity exponentially decays with increasing pressure in perfect agreement with the studies reported in the literature at lower pressures. It is found, however, that fibrous coatings could resist hydrostatic pressures significantly higher than those of previously reported surfaces. Our observations indicate that superhydrophobic fibrous coatings could potentially be used for underwater applications.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sustainability of superhydrophobicity under pressure

2012

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“…The pressure beyond which the surface undergoes a global transition from the Cassie state to the Wenzel state [62], and therefore could no longer generate drag reduction. Note that the terminal pressure differs from the critical pressure.…”

Section: Air-water Meniscus Stability Under Hydrostatic Pressurementioning

confidence: 99%

“…One can produce a superhydrophobic surface by randomly depositing hydrophobic aerogel particles on a substrate [59][60][61]. Samaha et al [62] prepared aerogel superhydrophobic surfaces with different particle sizes. Aerogel beads made of amorphous silicon dioxide having almost 99.8% porosity were ground and filtered through four stages of sieves with mesh sizes of 43, 104, 150, and 210 µm to prepare four categories of aerogel particles.…”

Section: Engineered Cost-effective Surfacesmentioning

confidence: 99%

Polymeric Slippery Coatings: Nature and Applications

Samaha

Gad‐el‐Hak

2014

Polymers

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Abstract: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 submerged surface with air-water interface, which is responsible for the slip effect. Suberhydrophobicity enhances the mobility of droplets on lotus leaves for self-cleaning purposes, so-called lotus effect. Amongst other applications, superhydrophobicity could be used to design slippery surfaces with minimal skin-friction drag for energy conservation. Another kind of slippery coatings is the recently invented slippery liquid-infused porous surfaces (SLIPS), which are one type of omniphobic surfaces. Certain plants such as the carnivorous Nepenthes pitcher inspired SLIPS. Their interior surfaces have microstructural roughness, which can lock in place an infused lubricating liquid. The lubricant is then utilized as a repellent surface for other liquids such as water, blood, crude oil, and alcohol. In this review, we discuss the concepts of both lotus effect and Nepenthes slippery mechanism. We then present a review of recent advances in manufacturing polymeric and non-polymeric slippery surfaces with ordered and disordered micro/nanostructures. Furthermore, we discuss the performance and longevity of such surfaces. Techniques used to characterize the surfaces are also detailed. We conclude the article with an overview of the latest advances in characterizing and using slippery surfaces for different applications.

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“…Figure 1b shows water droplet CA on different Polystyrene coatings with having the same average fiber diameter but different average fibers spacing. Note that as fiber spacing varies significantly across each coating, we used solid area fraction (SAF) to characterize the density of the fibers in each coating (see [36] for more information on obtaining SAF values from SEM images) as the best alternative, although we recognize that fiber spacing and SAF are only weakly correlated. The experimental measurements given in this figure indicate that apparent contact angle generally decreases with increasing SAF but the trend is not monotonic due to variety of reasons, some of which will be discussed later in this paper.…”

Section: Introductionmentioning

confidence: 99%

Modeling Cassie droplets on superhydrophobic coatings with orthogonal fibrous structures

Amrei

Dotivala

Tang

et al. 2017

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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Superhydrophobic coatings comprised of orthogonally layered fibers are studied in this paper in terms of their ability to accommodate water droplets at the non-wetting Cassie state. The effects of microstructural properties of these coatings on droplet contact angles and Cassie state stability are investigated via numerical simulation. More specifically, mathematical expressions are derived to predict whether or not such fibrous coatings can provide sufficient capillary forces for the droplet to remain in the Cassie state. For comparison, similar coatings comprised of parallel fibers are also studied, as a droplet may only interact with the first layer of fibers (parallel fibers) when the fiber spacing is smaller than some critical spacing value. Considerable differences were observed between droplet contact angles on coatings made of orthogonally layered fibers and those having multiple layers of parallel fibers. Our numerical simulations conducted using the Surface Evolver finite element code indicated that apparent contact angle of a droplet can be different in longitudinal and transverse directions, and they both increase by decreasing the diameter of the fibers or by increasing their spacing. It was also found that contact angle in the longitudinal direction is more sensitive to the spacing or the diameter of the fibers. It was also found that a droplet may achieve higher contact angles on a coating with orthogonally layered fibers than on its parallel-fiber counterpart.

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Effects of hydrostatic pressure on the drag reduction of submerged aerogel-particle coatings

Cited by 33 publications

References 39 publications

Sustainability of superhydrophobicity under pressure

Sustainability of superhydrophobicity under pressure

Polymeric Slippery Coatings: Nature and Applications

Modeling Cassie droplets on superhydrophobic coatings with orthogonal fibrous structures

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