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Communication Dans Un Congrès Année : 2013

Straight contact lines on soft solids and broken contact lines on hard substrates

Laurent Limat

Résumé

Despite decades of studies, wetting dynamics on a solid is still the focus of intense debates [1, 2]. The perhaps simplest wetting dynamics experiment consists in observing the shape of a drop sliding down an incline [3, 4]. Recent works have shown that a conical tail develop at the rear when the velocity is large enough, the stucture of both the flow and the interface being well described [5-7] by an appropriate generalization of the so-called hydrodynamical model of wetting [2]. On the other hand, depending on the liquid used, the slip cutoff assumed in these approachs can be of reasonable magnitude (polymer lengths for silicon oils) [3,7] or on the contrary, completely unreasonable, i.e. extremely small (water and mercury) [8-9]. In the first part of this talk, I suggest that this surprising result could be explained by assuming some extra-dissipation at small scale [1,12], that could be represented by a contact line friction in the framework of the combined model [10,11] that mixes the hydrodynamic approach [2] with thermally activated jumps [1]. In this framework, the large scale flow structure would be solely governed by hydrodynamics, while what happens at small scale involve an apparent cutoff modified by the contact line friction, and that can indeed be very small, when this line friction is sufficiently large. Another subject of passionate debates is also presently the static of wetting on soft solids [13-19]. In the 80's, Shanahan [32] developed a description in which the distorsions of the solid due to contact line assumed a logarithmic profile based on a balance between liquid surface tension and elastic stresses developing in the solid. At short scales, this profile was supposed to be cut by yield and plasticity. On the other hand, more recent approachs reveal that the surface tension of the solid, neglected in this initial approach, can not be omitted [15-18], especially when the substrate is very deformable, as happens for tenuous compounds such as gels [14,19]. In the second part of this talk, I will show that Shanahan approach can be modified [17] by adding this effect to the surface equilibrium equations. The same kind of logarithmic profile is obtained, but with a cutoff that is now ruled by the elastocapilary length built upon surface tension and elastic modulus. At small scale, the logarithmic divergence is replaced by the more classical condition of Neumann equilibrium of the three suface tensions at contact line, in agreement with other recent works [18].
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Dates et versions

hal-02379889 , version 1 (25-11-2019)

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  • HAL Id : hal-02379889 , version 1

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Laurent Limat. Straight contact lines on soft solids and broken contact lines on hard substrates. European Coating Symposium, ECS 2013, Joël de Coninck; Pierre Lambert; Didier Seveno; Terry D. Blake; Dorothée Friedrich; Fanny Lallemand, Sep 2013, Mons, Belgium. pp.57-59. ⟨hal-02379889⟩
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