Viscoelastic effects in the spreading of liquids

Carré, Alain; Gastel, Jean-Claude; Shanahan, M. E. R.

doi:10.1038/379432a0

Cited by 294 publications

(408 citation statements)

References 9 publications

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“…Our approach is justified here because ℓ=τ ∼ 0.25 mm=s for the silicone gel, whereas the reported speeds reach at most ∼ 100 nm=s. The large viscoelastic dissipation in the gel exceeds the dissipation within the drop by orders of magnitude, and explains these extremely slow drop velocities observed experimentally (21,35). In this case, it was also shown that all of the dissipation occurs in a very narrow region around the wetting ridge (21).…”

Section: Significancementioning

confidence: 61%

Liquid drops attract or repel by the inverted Cheerios effect

Karpitschka

Pandey

Lubbers

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

115

124

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Solid particles floating at a liquid interface exhibit a long-ranged attraction mediated by surface tension. In the absence of bulk elasticity, this is the dominant lateral interaction of mechanical origin. Here, we show that an analogous long-range interaction occurs between adjacent droplets on solid substrates, which crucially relies on a combination of capillarity and bulk elasticity. We experimentally observe the interaction between droplets on soft gels and provide a theoretical framework that quantitatively predicts the interaction force between the droplets. Remarkably, we find that, although on thick substrates the interaction is purely attractive and leads to dropdrop coalescence, for relatively thin substrates a short-range repulsion occurs, which prevents the two drops from coming into direct contact. This versatile interaction is the liquid-on-solid analog of the "Cheerios effect." The effect will strongly influence the condensation and coarsening of drops on soft polymer films, and has potential implications for colloidal assembly and mechanobiology.elastocapillarity | wetting | soft matter | mechanosensing | droplets T he long-ranged interaction between particles trapped at a fluid interface is exploited for the fabrication of microstructured materials via self-assembly and self-patterning (1-5) and occurs widely in the natural environment when living organisms or fine particles float on the surface of water (6, 7). In a certain class of capillary interactions, the particles deform the interface because of their shape or chemical heterogeneity (8)(9)(10). In this case, the change in interfacial area upon particle-particle approach causes an attractive capillary interaction between the particles. In the so-called Cheerios effect, the interaction between floating objects is mainly due to the change in gravitational potential energy associated to the weight of the particles, which deform the interface while being supported by surface tension (11), and the same principle applies when the interface is elastic (12-14). The name "Cheerios effect" is reminiscent of breakfast cereals floating on milk and sticking to each other or to the walls of the breakfast bowl.Here, we consider a situation opposite to that of the Cheerios effect, liquid drops deposited on a solid. The solid is sufficiently soft to be deformed by the surface tension of the drops, resulting in a lateral interaction. Recent studies have provided a detailed view of statics of single-drop wetting on deformable surfaces (15-19). The length scale over which the substrate is deformed is set by the ratio of the droplet surface tension γ and the substrate shear modulus G. The deformation can be seen as an elastocapillary meniscus, or "wetting ridge," around the drop (Fig. 1 A and B). Interestingly, the contact angles at the edge of the drop are governed by Neumann's law, just as for oil drops floating on water. In contrast to the statics of soft wetting, its dynamics has only been explored recently. New effects such as stick-slip motion induced...

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Section: Significancementioning

confidence: 61%

Liquid drops attract or repel by the inverted Cheerios effect

Karpitschka

Pandey

Lubbers

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

115

124

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“…Elastic deformations take place over a length on the order of the elastocapillary length γ/E, where γ is the liquid surface tension and E the solid Young's modulus. Recent experiments have considered liquids on very soft elastomers with γ/E of the order of 1-100 microns and have reported many interesting features, such as the geometry near the contact line Jerison et al 2011;Style et al 2013a), compression of the solid (Marchand et al 2012a), evaporation and spreading dynamics (Carre et al 1996;Li et al 2007;Sokuler et al 2010), as well as migration of droplets on substrates with a stiffness gradient (Style et al 2013b).…”

Section: Introductionmentioning

confidence: 99%

Drops on soft solids: free energy and double transition of contact angles

et al. 2014

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The equilibrium shape of liquid drops on elastic substrates is determined by minimising elastic and capillary free energies, focusing on thick incompressible substrates. The problem is governed by three length scales: the size of the drop R, the molecular size a, and the ratio of surface tension to elastic modulus γ/E. We show that the contact angles undergo two transitions upon changing the substrates from rigid to soft. The microscopic wetting angles deviate from Young's law when γ/Ea 1, while the apparent macroscopic angle only changes in the very soft limit γ/ER 1. The elastic deformations are worked out in the simplifying case where the solid surface energy is assumed constant. The total free energy turns out lower on softer substrates, consistent with recent experiments.

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“…Another reason for deformation is the unsatisfied normal component of the Young's equation giving rise to protrusions at the three-phase contact line. [24][25][26][27][28] This results in an increase in the force required to slide a drop on the solid surface as can be measured using the centrifugal adhesion balance. 3,4,26,29 Mutual saturation between phases or preferential adsorption at interfaces can be very fast, but sometimes, it occurs as a very slow process and thus exceeds the time of contact angle measurements, resulting in data measured under non-equilibrium conditions.…”

mentioning

confidence: 99%

Physics and applications of superhydrophobic and superhydrophilic surfaces and coatings

Drelich

Marmur

2014

Surface Innovations

153

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The terms superhydrophobicity and superhydrophilicity were introduced not very long ago, in 1996 and 2000, respectively.The former is used to describe exceptionally weak and the latter used to indicate strong interactions of materials and IntroductionAfter more than two centuries of research, capillarity and wetting phenomena still remain popular topics of investigation in many modern surface chemistry laboratories. Curiosity and fascination with rain droplets splashing in a puddle, water droplets decorating flowers, leaves of plants and fruits after rain or watering and colorful soap bubbles shaped at the end of wheat straw have never been stronger and go beyond scientific laboratories. Colorful images of liquid droplets and puddles, illustrating their behavior on a variety of surfaces, thrive in professional journals, popular magazines and Internet. However, terms such as wetting, spreading and contact angle are still puzzling to the layman and beginner researcher. To facilitate

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Viscoelastic effects in the spreading of liquids

Cited by 294 publications

References 9 publications

Liquid drops attract or repel by the inverted Cheerios effect

Liquid drops attract or repel by the inverted Cheerios effect

Drops on soft solids: free energy and double transition of contact angles

Physics and applications of superhydrophobic and superhydrophilic surfaces and coatings

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