Review of Fluid Slip over Superhydrophobic Surfaces and Its Dependence on the Contact Angle

Voronov, Roman S.; Papavassiliou, Dimitrios V.; Lee, Lloyd L.

doi:10.1021/ie0712941

Cited by 264 publications

(162 citation statements)

References 182 publications

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“…Over the last decade interest in the potential application of superhydrophobic surfaces for drag reduction has grown (Neto et al 2005;Voronov, Papavassiliou & Lee 2008;Quéré 2008;Vinogradova & Dubov 2012). Superhydrophobic surfaces are structured surfaces with micro-or nano-scale roughness that have a hydrophobic surface chemistry (McHale, Newton & Shirtcliffe 2010).…”

Section: Introductionmentioning

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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Section: Introductionmentioning

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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“…(5)] and thus a higher contact angle θ ∞ , but it leads to an enhanced energy barrier and thus a reduced slip length [32]. This insight may help understanding the observed controversial correlations between the contact angle and the slip length in experiments [42,44].…”

Section: Fig 2 Summarized the Contact Angles Of The Water Droplets Wmentioning

confidence: 96%

“…It is thus interesting to investigate the correlation between the wettability and the slip length. It is often believed that a hydrophobic surface often has a larger slip length than that of a hydrophilic surface [42].…”

Section: Fig 2 Summarized the Contact Angles Of The Water Droplets Wmentioning

confidence: 99%

Control of surface wettability via strain engineering

et al. 2013

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Reversible control of surface wettability has wide applications in lab-on-chip systems, tunable optical lenses, and microfluidic tools. Using a graphene sheet as a sample material and molecular dynamic (MD) simulations, we demonstrate that strain engineering can serve as an effective way to control the surface wettability. The contact angles θ of water droplets on a graphene vary from 72.5 • to 106 • under biaxial strains ranging from −10% to 10% that are applied on the graphene layer. For an intrinsic hydrophilic surface (at zero strain), the variation of θ upon the applied strains is more sensitive, i.e., from 0 • to 74.8 • . Overall the cosines of the contact angles exhibit a linear relation with respect to the strains. In light of the inherent dependence of the contact angle on liquid-solid interfacial energy, we develop an analytic model to show the cos θ as a linear function of the adsorption energy E ads of a single water molecule over the substrate surface. This model agrees with our MD results very well. Together with the linear dependence of E ads on biaxial strains, we can thus understand the effect of strains on the surface wettability. Thanks to the ease of reversibly applying mechanical strains in micro/nano-electromechanical systems (MEMS/NEMS), we believe that strain engineering can be a promising means to achieve the reversibly control of surface wettability.

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“…One expected difference between PDMS and PMMA resides in channel wettability. 16,17 The velocity profile measured in a microchannel with hydrophilic walls (PMMA 18 ) is different from that measured in microchannels with hydrophobic walls (PDMS): 17 hydrophobicity enhances the wall slip phenomenon, and, therefore, velocity and stress profiles within the channel cross-section will both be affected. In this regard, Graca et al 19 showed that PDMS hydrophobicity can be finely tuned by adding surfactants: even a small amount of surfactants (1 mM concentration) strongly increases channel wettability, as shown by the pronounced decrease of the measured contact angle.…”

Section: Introductionmentioning

confidence: 99%

Is microrheometry affected by channel deformation?

et al. 2016

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Microrheometry is very important for exploring rheological behaviours of several systems when conventional techniques fail. Microrheometrical measurements are usually carried out in microfluidic devices made of Poly(dimethylsiloxane) (PDMS). Although PDMS is a very cheap material, it is also very easy to deform. In particular, a liquid flowing in a PDMS device, in some circumstances, can effectively deform the microchannel, thus altering the flow conditions. The measure of the fluid relaxation time might be performed through viscoelasticity induced particle migration in microfluidics devices. If the channel walls are deformed by the flow, the resulting measured value of the relaxation time could be not reliable. In this work, we study the effect of channel deformation on particle migration in square-shaped microchannel. Experiments are carried out in several PolyEthylene Oxyde solutions flowing in two devices made of PDMS and Poly(methylmethacrylate) (PMMA). The relevance of wall rigidity on particle migration is investigated, and the corresponding importance of wall rigidity on the determination of the relaxation time of the suspending liquid is examined. V C 2016 AIP Publishing LLC. [http://dx

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Review of Fluid Slip over Superhydrophobic Surfaces and Its Dependence on the Contact Angle

Cited by 264 publications

References 182 publications

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

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

Control of surface wettability via strain engineering

Is microrheometry affected by channel deformation?

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