Computation of constant mean curvature surfaces: Application to the gas–liquid interface of a pressurized fluid on a superhydrophobic surface

Lobaton, E J; Salamon, Todd

doi:10.1016/j.jcis.2007.05.059

Cited by 73 publications

(101 citation statements)

References 34 publications

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“…13,14,25 For the pillared substrates, R should be replaced by the effective capillary radius R eff c defined by…”

Section: Morphologies Of Liquid−air Interfacementioning

confidence: 99%

“…This is the reason it is generally accepted that the wetting transition appears on an open-structured surface when the depinning happens. 11,14,25 By comparison with the CB state (from P1 to P2), the depinned metastable state (from P2 to B as illustrated by eq 13 and Figure 3c) can withstand relatively smaller disturbances. This is because this state has higher free energy than the Wenzel sate (from C to D).…”

Section: Stabilities Of Equilibrium Statesmentioning

confidence: 99%

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Importance of Hierarchical Structures in Wetting Stability on Submersed Superhydrophobic Surfaces

et al. 2012

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Submersed superhydrophobic surfaces exhibit great potential for reducing flow resistance in microchannels and drag of submersed bodies. However, the low stability of liquid−air interfaces on those surfaces limits the scope of their application, especially under high liquid pressure. In this paper, we first investigate the wetting states on submersed hydrophobic surfaces with one-level structure under hydrostatic pressure. Different equilibrium states based on free-energy minimization are formulated, and their stabilities are analyzed as well. Then, by comparison with the existing numerical and experimental studies, we confirm that a new metastable state, which happens after depinning of the three-phase contact line (TCL), exists. Finally, we show that a strategy of using hierarchical structures can strengthen the TCL pinning of the liquid−air interface in the metastable state. Therefore, the hierarchical structure on submersed surfaces is important to further improve the stability of superhydrophobicity under high liquid pressure.

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“…13,14,25 For the pillared substrates, R should be replaced by the effective capillary radius R eff c defined by…”

Section: Morphologies Of Liquid−air Interfacementioning

confidence: 99%

Section: Stabilities Of Equilibrium Statesmentioning

confidence: 99%

Importance of Hierarchical Structures in Wetting Stability on Submersed Superhydrophobic Surfaces

et al. 2012

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“…As a result, the shape of the interface changes with streamwise position as well. A recent study showed that for a meniscus supported between two parallel ribs of cavity spacing w c , the upper limit on the pressure that can be withstood by the surface without partial wetting of the cavity walls is (Lobaton and Salamon 2007)…”

Section: Introductionmentioning

confidence: 99%

“…It is important to note that reference to two contact angles is commonly made. The first value (h) is the local contact angle that exists at the interface of a liquid droplet with a smooth surface, and is the value that typically appears in Young's equation (Lobaton and Salamon 2007). The second value is the apparent contact angle that exists for a liquid droplet on a roughened or patterned surface (h CB ).…”

Section: Introductionmentioning

confidence: 99%

Liquid flow through microchannels with grooved walls under wetting and superhydrophobic conditions

Woolford

Maynes

Webb

2008

Microfluid Nanofluid

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Recent developments in superhydrophobic surfaces have enabled significant reduction in the frictional drag for liquid flow through microchannels. There is an apparent risk when using such surfaces, however, that under some conditions the liquid meniscus may destabilize and, consequently, the liquid will wet the entire patterned surface. This paper presents analytical and experimental results that compare the laminar flow dynamics through microchannels with superhydrophobic walls featuring ribs and cavities oriented both parallel and transverse to the direction of flow under both wetting and non-wetting conditions. The results show the reduction in the total frictional resistance is much greater in channels when the liquid phase does not enter the cavity regions. Further, it is demonstrated that the wetting and non-wetting cavity results represent limiting cases between which the experimental data lie. Generalized expressions enabling prediction of the classical friction factor-Reynolds number product as a function of the relevant governing dimensionless parameters are also presented for both the superhydrophobic and wetting states. Experimental results are presented for a range of parameters in the laminar flow regime.

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“…Usually, only one of these states is stable while the other is metastable [3][4][5], depending on both the surface chemistry and roughness. It is well known that wetting in the Cassie-Baxter, rather than Wenzel, state is energetically favorable if the hydrophobic surface is sufficiently rough [3][4][5][6] and this is generally considered to be a requirement for achieving superhydrophobicity [7]. In both states, minimizing the system free energy can yield apparent contact angles, θ * , that are functions of the intrinsic or chemical contact angle θ (measured on flat solids) and the topography of the roughness structure.…”

mentioning

confidence: 99%

Small is beautiful, and dry

Zheng

Hao

et al. 2010

Sci. China Phys. Mech. Astron.

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Thousands of plant and animal species have been observed to have superhydrophobic surfaces that lead to various novel behaviors. These observations have inspired attempts to create artificial superhydrophobic surfaces, given that such surfaces have multitudinous applications. Superhydrophobicity is an enhanced effect of surface roughness and there are known relationships that correlate surface roughness and superhydrophobicity, based on the underlying physics. However, while these examples demonstrate the level of roughness they tell us little about the independence of this effect in terms of its scale. Thus, they are not capable of explaining why such naturally occurring surfaces commonly have micron-submicron sizes. Here we report on the discovery of a new relation, its physical basis and its experimental verification. The results reveal that scaling-down roughness into the micro-submicron range is a unique and elegant strategy to not only achieve superhydrophobicity but also to increase its stability against environmental disturbances. This new relation takes into account the previously overlooked but key fact that the accumulated line energy arising from the numerous solid-water-air intersections that can be distributed over the apparent contact area, when air packets are trapped at small scales on the surface, can dramatically increase as the roughness scale shrinks. This term can in fact become the dominant contributor to the surface energy and so becomes crucial for accomplishing superhydrophobicity. These findings guide fabrication of stable super water-repellant surfaces. scale effect, line tension, wetting, contact angle, superhydrophobic PACS: 47.55.np, 47.55.dr, 68.08.Bc, 68.03.Cd, 87.15.LaWetting on a rough substrate is considered to be either in the Wenzel [1] or Cassie-Baxter state [2]. In the former, the liquid follows the surface corrugations, as shown in Figure 1(a); in the latter the water drop is attached to the surface but in a position on top of the corrugations, which allows air pockets to be trapped under it, as shown in Figure 1(b). Usually, only one of these states is stable while the other is metastable [3][4][5], depending on both the surface chemistry and roughness. It is well known that wetting in the Cassie-Baxter, rather than Wenzel, state is energetically favorable if the hydrophobic surface is sufficiently rough [3][4][5][6] and this is generally considered to be a requirement for achieving superhydrophobicity [7]. In both states, minimizing the system free energy can yield apparent contact angles, θ * , that are functions of the intrinsic or chemical contact angle θ (measured on flat solids) and the topography of the roughness structure. Chemically modifying the surface alone can typically lead to intrinsic contact angles of up to 120°, but not more [8,9]. The relation between the apparent and intrinsic contact angles in the Wenzel state is given by cosθ * = rcosθ. The parameter r is the ratio of the wet surface area to its projection or apparent area. In the Cassie-Baxter stat...

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Computation of constant mean curvature surfaces: Application to the gas–liquid interface of a pressurized fluid on a superhydrophobic surface

Cited by 73 publications

References 34 publications

Importance of Hierarchical Structures in Wetting Stability on Submersed Superhydrophobic Surfaces

Importance of Hierarchical Structures in Wetting Stability on Submersed Superhydrophobic Surfaces

Liquid flow through microchannels with grooved walls under wetting and superhydrophobic conditions

Small is beautiful, and dry

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