How the local defect of triple line (kink) rules the scaling of receding contact angles on periodic superhydrophobic surfaces

Dans le cadre du cycle de conférences mis en oeuvre par le Laboratoire de Physique de la Matière Condensée. Jérémie Teisseire sera cette semaine à l'honneur
Quand ? Le 09-07-2015,
de 11:00 à 12:00
Où ? LPMC Salle C Brot
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The control of pinning and spreading of a liquid, usually water, on a surface are major issues for many applications. It is well-known that in nature, self-cleaning surfaces possess micro- or nano- structures with a multi-scale roughness, on which the drops remain suspended to the top of the structure without impregnation in the micro-structure (Cassie state). This situation leads to high mobility of the drop which is the basics of the so-called “lotus effect”. Many fabrication processes have been proposed to make such surfaces associating a multi-scale roughness controlled by a low surface energy. However, the structure design is empiric because the relation between functionalization and structure morphology is ill understood. In this work we will present a process based on nanoimprint to add silica patterned layers on glass substrate. To understand the relation between wetting and surface roughness, contact angles were measured on periodic super-hydrophobic surfaces. Investigating different types of lattices, including anisotropic ones, we found that effective adhesion scales with surface fraction (and not with line fraction). This surprising behavior is closely related to the deformations of the contact line. Numerical and analytical modeling demonstrates that the relevant mechanism is pinning through triple line defects which we interpret in term of propagation of kink along the lattice.

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