Interaction of Droplets Separated by an Elastic Film

Liu, Tianshu; Xu, Xuejuan; Nadermann, Nichole; He, Zhenping; Jagota, Anand; Hui, Chung‐Yuen

doi:10.1021/acs.langmuir.6b03600

Cited by 12 publications

(9 citation statements)

References 51 publications

(62 reference statements)

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“…From the observation of the apparent contact angles, the tension in the membrane may be measured, which may allow to infer the surface stress of the elastomer (Nadermann et al, 2013). Droplets deposited on opposite sides of the membranes interact through the out-of-plane deformation of the membrane that they induce, and therefore spontaneously assemble (Liu et al, 2017).…”

Section: A) B)mentioning

confidence: 99%

Elastocapillarity: When Surface Tension Deforms Elastic Solids

Bico

Reyssat

Roman

2018

Annu. Rev. Fluid Mech.

245

195

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Although negligible at large scales, capillary forces may become dominant for submillimetric objects. Surface tension is usually associated with the spherical shape of small droplets and bubbles, wetting phenomena, imbibition or the motion of insects at the surface of water. However, beyond liquid interfaces, capillary forces can also deform solid bodies in their bulk as observed in recent experiments with very soft gels. Capillary interactions, which are responsible for the cohesion of sand castles, can also bend slender structures and induce the bundling of arrays of fibres. Thin sheets can finally spontaneously wrap liquid droplets within the limit of the constraints dictated by di↵erential geometry. The aim of this review is to describe the di↵erent scaling parameters and characteristic lengths involved in "elastocapillarity". We focus successively on three main configurations: • 3D, deformations induced in bulk solids • 1D, bending and bundling of rod-like structures • 2D, bending and stretching of thin sheets Although each configuration would deserve a detailed review, we hope our broad description will provide a general view on elastocapillarity.

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Section: A) B)mentioning

confidence: 99%

Elastocapillarity: When Surface Tension Deforms Elastic Solids

Bico

Reyssat

Roman

2018

Annu. Rev. Fluid Mech.

245

195

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“…For instance, when the substrate is replaced by a soft solid, elastocapillary interactions lead to deviations from the classical Young-Dupré's law due to the formation of a wetting ridge at the contact line [2][3][4][5][6][7][8][9]. The substrate can also be replaced by a thin free-standing elastic film, serving as a compliant boundary for the droplet [10][11][12][13][14][15][16][17]. In this geometry, the contact angles are set by a Neumann construction with mechanical and interfacial tensions balanced at the contact line [11,12,14,16,17].…”

mentioning

confidence: 99%

Droplets Capped with an Elastic Film Can Be Round, Elliptical, or Nearly Square

Schulman

Dalnoki-Veress

2018

Phys. Rev. Lett.

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We present experiments which show that the partial wetting of droplets capped by taut elastic films is highly tunable. Adjusting the tension allows the contact angle and droplet morphology to be controlled. By exploiting these elastic boundaries, droplets can be made elliptical, with an adjustable aspect ratio, and can even be transformed into a nearly square shape. This system can be used to create tunable liquid lenses, and moreover, presents a unique approach to liquid patterning.Wetting has been the subject of intense research for well over a century, motivated largely by industrial applications, ranging from designing tires to treating textiles and choosing coatings for surfaces, but also by the academic interest in a field which is undeniably rich [1]. A common theme in wetting phenomena is that boundary conditions and substrate play a pivotal role. For instance, when the substrate is replaced by a soft solid, elastocapillary interactions lead to deviations from the classical Young-Dupré's law due to the formation of a wetting ridge at the contact line [2][3][4][5][6][7][8][9]. The substrate can also be replaced by a thin free-standing elastic film, serving as a compliant boundary for the droplet [10][11][12][13][14][15][16][17]. In this geometry, the contact angles are set by a Neumann construction with mechanical and interfacial tensions balanced at the contact line [11,12, 14,16,17].Compliant elastic surfaces also show novel wetting behaviours and morphologies. For instance, droplets have been observed to migrate towards regions of increased compliance [18][19][20], and interact with other droplets due to deformations induced in the elastic films [15,21]. Dewetting liquid films capped by a thin elastic layer can have their dynamics and dewetting morphologies controlled by adjusting the tension [23]. Anisotropic tension in a supporting free-standing film causes sessile droplets to elongate along the high tension direction, and thus, droplets map out the stress field in the elastomer [17]. Furthermore, droplets pressed between a rigid surface and a soft solid acquire the shape of a flattened ellipsoid [22].Although partial wetting on soft or compliant solids has received significant attention, here, we examine partial wetting in a novel geometry wherein droplets are capped by a thin elastic film under tension. This system could serve as a model for blisters or droplets trapped beneath drying paint [24]. We show that the contact angle of these droplets decreases with increased tension which is well described through an analogy made with Young-Dupré's law which incorporates mechanical tension. The model contains a free parameter from which the elastomer-liquid interfacial tension may be determined. We extract reasonable values for this quantity for four different liquid-solid combinations. Finally, we show that biaxial stresses in the capping elastic boundary can produce elliptical droplets with tuneable aspect ratio, and even droplets with nearly-square morphology using a suitable sample geometry.Thin elast...

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“…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.…”

mentioning

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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Interaction of Droplets Separated by an Elastic Film

Cited by 12 publications

References 51 publications

Elastocapillarity: When Surface Tension Deforms Elastic Solids

Elastocapillarity: When Surface Tension Deforms Elastic Solids

Droplets Capped with an Elastic Film Can Be Round, Elliptical, or Nearly Square

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

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