Slippage of Water Past Superhydrophobic Carbon Nanotube Forests in Microchannels

Joseph, Pierre; Cottin-Bizonne, Cécile; Benoit, Jean‐Michel; Ybert, Christophe; Journet, Catherine; Tabeling, Patrick; Bocquet, Lydéric

doi:10.1103/physrevlett.97.156104

Cited by 419 publications

(373 citation statements)

References 21 publications

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“…Whereas the slip and viscous drag reduction have been extensively characterized in continuous flows by, for example, nanorheological measurements 22 and particle image velocimetry 23 , considerably less is known about the friction and dissipation in discrete droplets. This can be considered to originate from the contemporary characterization methods, such as the optical contact angle goniometry, that measure static or quasistatic properties of the interfaces and contact angles 24 .…”

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confidence: 99%

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

et al. 2013

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The recently demonstrated extremely water-repellent surfaces with contact angles close to 180°with nearly zero hysteresis approach the fundamental limit of non-wetting. The measurement of the small but non-zero energy dissipation of a droplet moving on such a surface is not feasible with the contemporary methods, although it would be needed for optimized technological applications related to dirt repellency, microfluidics and functional surfaces. Here we show that magnetically controlled freely decaying and resonant oscillations of water droplets doped with superparamagnetic nanoparticles allow quantification of the energy dissipation as a function of normal force. Two dissipative forces are identified at a precision of B10 nN, one related to contact angle hysteresis near the three-phase contact line and the other to viscous dissipation near the droplet-solid interface. The method is adaptable to common optical goniometers and facilitates systematic and quantitative investigations of dynamical superhydrophobicity, defects and inhomogeneities on extremely superhydrophobic surfaces.

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confidence: 99%

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

et al. 2013

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“…Due to the lower dynamic viscosity of air compared to water the trapped air layer on a superhydrophobic surface has a lubricating effect on the flow over it. Drag reducing properties of superhydrophobic surfaces have been observed experimentally in microfluidic devices (Choi, Westin & Breuer 2003;Ou, Perot & Rothstein 2004;Ou & Rothstein 2005;Joseph et al 2006;Daniello, Waterhouse & Rothstein 2009;Govardhan et al 2009;Tsai et al 2009;Rothstein 2010) and for coated objects, such as hydrofoils (Gotge et al 2005), settling spheres (McHale et al 2009) and cylinders (Muralidhar et al 2011), covering flow regimes from laminar to turbulent. In a stable configuration, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…using µ-PIV measurements (Ou & Rothstein 2005;Joseph et al 2006;Truesdell et al 2006;Tsai et al 2009), the slip length at the wall can be computed using relation (3.9) based on the wall velocity The diamonds show the optimum gas layer thickness/maximum drag reduction, whereas the circles and squares indicate the gas layer thicknesses needed to achieve 90 and 50 % of the maximum drag reduction.…”

Section: Slip Length Based On Velocity Profilementioning

confidence: 99%

Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface

et al. 2013

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Analytic results are derived for the apparent slip length, the change in drag and the optimum air layer thickness of laminar channel and pipe flow over an idealised superhydrophobic surface, i.e. a gas layer of constant thickness retained on a wall. For a simple Couette flow the gas layer always has a drag reducing effect, and the apparent slip length is positive, assuming that there is a favourable viscosity contrast between liquid and gas. In pressure-driven pipe and channel flow blockage limits the drag reduction caused by the lubricating effects of the gas layer; thus an optimum gas layer thickness can be derived. The values for the change in drag and the apparent slip length are strongly affected by the assumptions made for the flow in the gas phase. The standard assumptions of a constant shear rate in the gas layer or an equal pressure gradient in the gas layer and liquid layer give considerably higher values for the drag reduction and the apparent slip length than an alternative assumption of a vanishing mass flow rate in the gas layer. Similarly, a minimum viscosity contrast of four must be exceeded to achieve drag reduction under the zero mass flow rate assumption whereas the drag can be reduced for a viscosity contrast greater than unity under the conventional assumptions. Thus, traditional formulae from lubrication theory lead to an overestimation of the optimum slip length and drag reduction when applied to superhydrophobic surfaces, where the gas is trapped.

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“…Regular arrays of chemical patches [4,5,6] and posts [7,8,9,10] of different shapes and sizes are regularly fabricated and several authors [11,12,13] have even shown the possibilities of manufacturing multi-scale surface patterns. Recently such patterning has been used to control the movement of drops [16,17] and to attempt to enhance flow in microchannels [18,19].…”

Section: Introductionmentioning

confidence: 99%

Anisotropic Drop Morphologies on Corrugated Surfaces

et al. 2008

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The spreading of liquid drops on surfaces corrugated with micron-scale parallel grooves is studied both experimentally and numerically. Because of the surface patterning, the typical final drop shape is no longer spherical. The elongation direction can be either parallel or perpendicular to the direction of the grooves, depending on the initial drop conditions. We interpret this result as a consequence of both the anisotropy of the contact line movement over the surface and the difference in the motion of the advancing and receding contact lines. Parallel to the grooves, we find little hysteresis due to the surface patterning and that the average contact angle approximately conforms to Wenzel's law as long as the drop radius is much larger than the typical length scale of the grooves.

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Slippage of Water Past Superhydrophobic Carbon Nanotube Forests in Microchannels

Cited by 419 publications

References 21 publications

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity

Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface

Anisotropic Drop Morphologies on Corrugated Surfaces

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