Effect of Capillary Pressure and Surface Tension on the Deformation of Elastic Surfaces by Sessile Liquid Microdrops: An Experimental Investigation

Pericet-Cámara, Ramón; Best, A.; Butt, Hans‐Jürgen; Bonaccurso, Elmar

doi:10.1021/la801862m

Cited by 178 publications

(170 citation statements)

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“…For smaller droplets, the shape of the wetting ridge is asymmetric, as has been observed experimentally [24]. As the droplet radius increases the shape of the wetting ridge becomes more symmetric.…”

Section: Solution For a Hemispherical Dropletsupporting

confidence: 67%

Static wetting on deformable substrates, from liquids to soft solids

Style¹,

Dufresne²

2012

Soft Matter

234

335

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Young's law fails on soft solid and liquid substrates where there are substantial deformations near the contact line. On liquid substrates, this is captured by Neumann's classic analysis, which provides a geometrical construction for minimising the interfacial free energy. On soft solids, the total free energy includes an additional contribution from elasticity. A linear-elastic model incorporating an out-of-plane restoring force due to solid surface tension was recently shown to accurately predict the equilibrium shape of a thin elastic film due to a large sessile droplet. Here, we extend this model to find substrate deformations due to droplets of arbitrary size. While the macroscopic contact angle matches Young's law for large droplets, it matches Neumann's prediction for small droplets. The cross-over droplet size is roughly given by the ratio of the solid's surface tension and elastic modulus. At this cross-over, the macroscopic contact angle increases, indicating that the substrate is effectively less wetting. For droplets of all sizes, the microscopic behaviour near the contact line follows the Neumann construction giving local force balance.

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Section: Solution For a Hemispherical Dropletsupporting

confidence: 67%

Static wetting on deformable substrates, from liquids to soft solids

Style¹,

Dufresne²

2012

Soft Matter

234

335

View full text Add to dashboard Cite

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“…For instance, studies on the partial wetting of liquid drops on soft solids show that Young's law is applicable on length scales much larger than the bulk elastocapillary length γ=E, where γ is the liquid-air surface tension and E is the Young's modulus of the solid. However, on smaller length scales, the contact line reveals a wetting ridge set by a Neumann construction involving surface stresses [20][21][22][23][24][25][26].Partial wetting on deformable substrates may also be studied by employing a highly compliant geometry, such as a droplet on a thin freestanding film [27][28][29][30][31]. These studies have considered clamped films which are held taut and support a uniform and isotropic tension.…”

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confidence: 99%

Liquid Droplets Act as “Compass Needles” for the Stresses in a Deformable Membrane

et al. 2017

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We examine the shape of droplets atop deformable thin elastomeric films prepared with an anisotropic tension. As the droplets generate a deformation in the taut film through capillary forces, they assume a shape that is elongated along the high tension direction. By measuring the contact line profile, the tension in the membrane can be completely determined. Minimal theoretical arguments lead to predictions for the droplet shape and membrane deformation that are in excellent agreement with the data. On the whole, the results demonstrate that droplets can be used as probes to map out the stress field in a membrane. DOI: 10.1103/PhysRevLett.118.198002 The physics of liquid droplets in contact with soft or deformable solids, elastocapillarity, is an active subject of research. Between capillary origami and wrinkling instabilities of thin films [1][2][3][4][5][6][7][8][9], the bending, coiling, and winding of slender structures [10][11][12][13][14][15][16], and elasticitymediated propulsion of droplets [17][18][19], there is no shortage of complexity, self-assembly, or beautiful examples of pattern formation in the field. In addition, some recent results have forced us to question familiar concepts of solid-liquid interactions. For instance, studies on the partial wetting of liquid drops on soft solids show that Young's law is applicable on length scales much larger than the bulk elastocapillary length γ=E, where γ is the liquid-air surface tension and E is the Young's modulus of the solid. However, on smaller length scales, the contact line reveals a wetting ridge set by a Neumann construction involving surface stresses [20][21][22][23][24][25][26].Partial wetting on deformable substrates may also be studied by employing a highly compliant geometry, such as a droplet on a thin freestanding film [27][28][29][30][31]. These studies have considered clamped films which are held taut and support a uniform and isotropic tension. As shown in Fig. 1(a), the Laplace pressure of the droplet creates a bulge in the film below it, in the shape of a spherical cap, which is of the same order in size as the droplet itself. The deformations generated may be orders of magnitude larger than the bulk elastocapillary length, because stretching of the membrane is the relevant mode of elasticity [28][29][30][31]. The contact line profile is determined by a Neumann construction, which incorporates both mechanical and interfacial tensions. This profile is characterized by the angles subtended by the liquid (θ d ) and bulge (θ b ) to the surrounding film [ Fig. 1(a)], which remains completely flat, i.e., the film's angle relative to the horizontal θ m ¼ 0. From the Neumann construction, these angles are set by two parameters: the Young's angle θ Y of the same solid supported on a rigid substrate and the ratio T in =γ, where T in is the total mechanical and interfacial tension acting inside the contact region of the membrane or drop system [31]. In the limit of infinite tension, the bulge vanishes and Young's law is recovered.In this stud...

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“…The presence of the ridge outside the droplet had been measured optically by several authors. [11][12][13][14] Only recently, however, Pericet-Camara et al 15 characterized and analyzed the entire deformation of a soft Sylgard Ò 184 surface by a sessile microdrop by means of laser scanning confocal microscopy (LSCM). Sylgard is an elastomer mainly consisting of poly(dimethylsiloxane) (PDMS).…”

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confidence: 99%

Solid-supported thin elastomer films deformed by microdrops

et al. 2009

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A sessile droplet can deform the surface of a soft solid not only with its weight. The surface tension pulls up a ridge at the perimeter of the drop, and the capillary pressure embosses a quasi-spherical dimple underneath the drop. This holds for the case of a bulk solid. However, if the solid forms a film with thickness comparable to the deformation scale the shape and the depth of the dimple are strongly distorted. We investigated dimples on elastomer films with a Young's modulus of 25 kPa and thickness in the range 4-104 mm embossed by sessile ionic liquid droplets. The films are supported by an undeformable glass slide. Below a certain critical film thickness, the dimple is shallower and the ridge at the drop rim is less elevated than for the bulk elastomer. The deviations are more pronounced for thinner films. Further, troughs form at the two sides of the ridge. Their distance from the rim is equivalent to the layer thickness. The measurements are qualitatively reproduced by an analytical model and quantitatively by numerical simulations. A consistent physical picture of the deformation on the bulk elastomer and of the distortions on the thin films is given.

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Effect of Capillary Pressure and Surface Tension on the Deformation of Elastic Surfaces by Sessile Liquid Microdrops: An Experimental Investigation

Cited by 178 publications

References 25 publications

Static wetting on deformable substrates, from liquids to soft solids

Static wetting on deformable substrates, from liquids to soft solids

Liquid Droplets Act as “Compass Needles” for the Stresses in a Deformable Membrane

Solid-supported thin elastomer films deformed by microdrops

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