Wicking within forests of micropillars

Ishino, C.; Reyssat, Mathilde; Reyssat, Étienne; Okumura, Ko; Quéré, David

doi:10.1209/0295-5075/79/56005

Cited by 184 publications

(203 citation statements)

References 13 publications

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“…The pioneering work of Hasimoto estimated the viscous resistance of the pillars to the fluid by idealizing the pillars as infinitely long cylinders. 21 Based on the Washburn law, Ishino et al 22 considered viscous dissipation on the substrate and the side walls, and obtained two extreme regimes for short and tall pillars, respectively. Then, Srivastava et al 23 and Xiao and Wang 24 developed Ishino's model and got a more accurate exponent.…”

Section: -3mentioning

confidence: 99%

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

2014

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The dynamic spreading of a liquid droplet on micropillar-arrayed surfaces is experimentally investigated. A theoretical model is proposed to include energy dissipations raised from both the viscous resistance at mesoscale and the molecular friction at microscale in the triple-phase region. The scaling laws and spreading shape of the droplet change with the variation of the liquid viscosity because of the competition between these two mechanisms of energy dissipations at the moving contact line. The Laplace pressures at the interior corner and at the wavy contact line are the answers to the excess driving energy and the superwetting on pillar-arrayed surfaces. The formation and evolution of the bulk and the fringe are also analyzed in detail. Our results may help to understand the wetting dynamics on microtextured surfaces and assist the future design of engineered surfaces in practical applications. C 2014 AIP Publishing LLC. [http://dx

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Section: -3mentioning

confidence: 99%

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

2014

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“…Whilst non-constant channel cross sections have been a focus of study experimentally and theoretically (Legait, 1983;Staples andShaffer, 2002, Reysatt et al, 2008;Liou et al, 2009), increased solid-liquid contact area, and hence increased capillary pull can be achieved using a range of in-channel structures. In a series of studies, Bico and co-workers studied imbibition using hemi-wicking, which amplifies the capillary pull using wall roughness (Bico 2000Bico and Quéré, 2003;Ishino et al, 2007); ideas recently applied to rough Cu 6 Sn 5 /Cu intermetallic surfaces (Liu et al, 2011). Their work used average parameters to characterize the capillary effect of roughness and topographic structures.…”

Section: Introductionmentioning

confidence: 99%

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Ouali

McHale

Javed

et al. 2013

Microfluid Nanofluid

149

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The spontaneous capillary-driven filling of microchannels is important for a wide range of applications. These channels are often rectangular in cross-section, can be closed or open, and horizontal or vertically orientated. In this work, we develop the theory for capillary imbibition and rise in channels of rectangular cross-section, taking into account rigidified and non-rigidified boundary conditions for the liquid-air interfaces and the effects of surface topography assuming Wenzel or Cassie-Baxter states. We provide simple interpolation formulae for the viscous friction associated with flow through rectangular cross-section channels as a function of aspect ratio. We derive a dimensionless cross-over time, T c , below which the exact numerical solution can be approximated by the Bousanquet solution and above which by the visco-gravitational solution. For capillary rise heights significantly below the equilibrium height, this cross-over time is T c  (3X e /2) 2/3 and has an associated dimensionless crossover rise height X c  (3X e /2) 1/3 , where X e =1/G is the dimensionless equilibrium rise height and G is a dimensionless form of the acceleration due to gravity. We also show from wetting considerations that for rectangular channels, fingers of a wetting liquid can be expected to imbibe in advance of the main meniscus along the corners of the channel walls. We test the theory via capillary rise experiments using polydimethylsiloxane oils of viscosity 96.0, 48.0, 19.2 and 4.8 mPa s within a range of closed square tubes and open rectangular cross-section channels with SU-8 walls. We show that the capillary rise heights can be fitted using the exact numerical solution and that these are similar to fits using the analytical visco-gravitational solution. The viscous friction contribution was found to be slightly higher than predicted by theory assuming a non-rigidified liquid-air boundary, but far below that for a rigidified boundary, which was recently reported for imbibition into horizontally mounted open microchannels. In these experiments we also observed fingers of liquid spreading along the internal edges of the channels in advance of the main body of liquid consistent with wetting expectations. We briefly discuss the implications of these observations for the design of microfluidic systems.

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“…The pioneering work of Hasimoto (1959) estimated the viscous resistance of the pillars to the fluid by idealizing the pillar arrays as infinitely long cylinders. Taking account of both the viscous resistance from the pillars and the substrate, Ishino et al did an elegant scaling analysis based on the Washburn law to obtain two extreme regimes for short and tall posts, respectively (Ishino et al 2007). Then, Srivastava et al (2010) and Xiao, Enright & Wang (2010) developed this model to be more accurate.…”

Section: Introductionmentioning

confidence: 99%

Multiscale dynamic wetting of a droplet on a lyophilic pillar-arrayed surface

2013

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Dynamic wetting of a droplet on lyophilic pillars was explored using a multiscale combination method of experiments and molecular dynamics simulations. The excess lyophilic area not only provided excess driving force, but also pinned the liquid around the pillars, which kept the moving contact line in a dynamic balance state every period of the pillars. The flow pattern and the flow field of the droplet on the pillar-arrayed surface, influenced by the concerted effect of the liquid-solid interactions and the surface roughness, were revealed from the continuum to the atomic level. Then, the scaling analysis was carried out employing molecular kinetic theory. Controlled by the droplet size, the density of roughness and the pillar height, two extreme regimes were distinguished, i.e. R ∼ t 1/3 for the rough surface and R ∼ t 1/7 for the smooth surface. The scaling laws were validated by both the experiments and the simulations. Our results may help in understanding the dynamic wetting of a droplet on a pillar-arrayed lyophilic substrate and assisting the future design of pillar-arrayed lyophilic surfaces in practical applications.

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Wicking within forests of micropillars

Cited by 184 publications

References 13 publications

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

Dynamic spreading on pillar-arrayed surfaces: Viscous resistance versus molecular friction

Wetting considerations in capillary rise and imbibition in closed square tubes and open rectangular cross-section channels

Multiscale dynamic wetting of a droplet on a lyophilic pillar-arrayed surface

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