Structure-induced spreading of liquid in micropillar arrays

Priest, Craig; Forsberg, Pontus; Sedev, Rossen; Ralston, John

doi:10.1007/s00542-011-1341-8

Cited by 10 publications

(10 citation statements)

References 42 publications

(46 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Aer hard baking (200 C, 5 min), the samples were treated with sulphuric acid at high concentrations (60-65% vol) to make the SU8 more hydrophilic. 13 The static advancing contact angle was then carefully measured on at (unstructured) regions of each sample using the sessile drop technique. On each sample, contact angles were extracted from between 12 and 15 images of droplets and averaged.…”

Section: Wicking Criteriamentioning

confidence: 99%

Pinning and wicking in regular pillar arrays

et al. 2014

Self Cite

View full text Add to dashboard Cite

Pinning and wicking of a liquid meniscus in a square array of pillars is investigated in numerical energy minimizations and compared to wetting experiments. Our combined study shows that criteria for spontaneous film formation, based on thermodynamic considerations as well as on simple geometric modelling of the meniscus shape, are insufficient to predict the onset of wicking. High aspect ratio pillars with a square cross-section may display a re-entrant pinning regime as the density of the pillars is increased, a behaviour that is captured by neither of the aforementioned models. Numerically computed energy landscapes for the advancing meniscus allow us to explain the re-entrant behaviour in terms of energy barriers between topologically different meniscus shapes. Our numerical results are validated by wicking experiments where for the material contact angle θ0 = 47° the re-entrant behaviour is present for square pillars and absent for pillars with circular cross section.

show abstract

Section: Wicking Criteriamentioning

confidence: 99%

Pinning and wicking in regular pillar arrays

et al. 2014

Self Cite

View full text Add to dashboard Cite

show abstract

“…Wenzel 2 predicted that when e 5 90 , a higher roughness ratio r leads to a larger value for cos W r , towards 1, thus giving a smaller value for W r , towards 0 . More recent studies by Bico et al 10 and Priest et al 11 discussed that e as a critical contact angle is not necessarily 90 but an angle lower than 90 , at around 75 . In this situation, as roughness factor r gets larger, the apparent contact angle would go towards 0 driven by the capillary action, effectively spreading or wicking the water drop on a surface.…”

mentioning

confidence: 97%

The effects of surface energy and roughness on the hydrophobicity of woven fabrics

Shim

Kim

Park

2014

Textile Research Journal

View full text Add to dashboard Cite

The wetting behavior of a hydrophobic rough surface is investigated on a surface fabricated by applying low surface tension materials such as silicone or fluoropolymer to polyester woven fabric consisting of multifilament yarns. The roughness factor of various woven fabrics can be calculated by Wenzel's and Cassie-Baxter's equations. For the fabrics treated with silicone or fluoropolymer, the Cassie-Baxter model was applied, showing a level of agreement for the fabric specimens non-textured filament fibers between the predicted contact angles and the measured values. More precisely, the fabrics treated with silicone or fluoropolymer represent the transitional state between the Wenzel type and the Cassie-Baxter type; that is, the fractional contact area between the water and air f 2 is greater than zero, and the sum of the fractional contact areas for solid-water f 1 and air-water f 2 is greater than 1. A surface with lower energy and higher roughness gave f 1 + f 2 close to 1 with smaller f 1 and larger f 2 , which resulted in a high contact angle. KeywordsHydrophobic, lotus effect, roughness factor, Wenzel model, Cassie-Baxter model Inspired by natural surfaces like the lotus leaf, surfaces with extreme water repellent properties have received considerable interest in the last decade. 1 The studies by Wenzel 2 and Cassie and Baxter 3 showed that the rough and porous structure of a surface combined with a low surface energy can contribute to the hydrophobicity of a surface. The surface of the lotus leaf is chemically made of wax and structurally has two levels of roughness consisting of nano-scale bumps on the surface of micro-scale protrusions that enables the trapping of air underneath water droplets, thereby contributing to a well-designed superhydrophobic surface. 4 Drops of water deposited on such superhydrophobic surfaces exhibit extremely high contact angles (>150 ) and roll off at slight inclinations. Potential applications range from non-wettable, quick-drying surfaces to anti-fouling or self-cleaning surfaces. 4-8 In view of the significant potential of such surfaces for numerous scientific and industrial applications, many strategies to create superhydrophobic surfaces have been published to date. [6][7][8][9] As a measure of the hydrophobicity of the fabric surface, the static contact angle is often used; a larger contact angle with a smaller contact angle hysteresis represents higher hydrophobicity. Wenzel 2 and Cassie and Baxter 3 suggested the theoretical models for contact angles of a liquid on a surface with certain geometry. 9 Different contact angles may result with the same roughness texture depending on how the liquid is configured on the surface. When a liquid completely fills all the spaces in the pores, the Wenzel model is applied to describe the contact angle W r as a function of the ratio of the liquid-solid contact area to the

show abstract

“…Imbibition angle is expressed in Eq. When a liquid spreads on a hydrophilic surface, there is generally a thin precursor liquid film ahead of macroscopic liquid motion [12,[140][141][142][143] . The behavior of the thin precursor liquid film is governed by long-range intermolecular forces between the molecules of the liquid and the molecules of the substrate [141] .…”

Section: Resultsmentioning

confidence: 99%

“…In this work, we focus on the motion of the micro-scale thin liquid film ahead of the bulk droplet, which spreads on slanted micro-pillar surfaces. On the microscopic scale, the behavior of droplets and streams of liquid in contact with solid walls is dominated by capillary pressure [143] . We find that when a droplet was deposited on a smooth surface or straight micro-pillars surface (Fig.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Asymmetric liquid wetting on controllable magnetic micro-pillar surfaces

Yang¹

View full text Add to dashboard Cite

Wetting is the ability of a liquid to maintain contact with a solid surface, and spreading is the displacement process from a surface of air or one fluid by another. The wetting and spreading is a ubiquitous phenomenon in nature and daily life and has attracted numerous research interests in many applications, such as lubrication, coating, painting and drug delivery. Unidirectional liquid wetting and spreading on asymmetric nanostructured surfaces was also reported recently, such as water droplets roll off rice leaves due to their anisotropic microstructured leaf surfaces. For developing new process and technologies in which wetting and

show abstract

Structure-induced spreading of liquid in micropillar arrays

Cited by 10 publications

References 42 publications

Pinning and wicking in regular pillar arrays

Pinning and wicking in regular pillar arrays

The effects of surface energy and roughness on the hydrophobicity of woven fabrics

Asymmetric liquid wetting on controllable magnetic micro-pillar surfaces

Contact Info

Product

Resources

About