Rebonds spéciaux de liquides

Abstract : This thesis revolves around the ability of liquid drops to bounce off superhydrophobic materials. We generate special rebounds and characterize them experimentally.We focus on finding the relevant physical phenomena to describe the temporal and spatial extension of such events, both quantities being of importance from the fundamental and applied point of vue. First, we study the influence of the susbtrate geometry. We modify the surface locally, by introducing a singular macrotexture, and show that it leads to a new bouncing mechanism that shortens the contact time by a factor typically 2. We also modify the substrate at the size of the drop. We perform impacts on non wetting cones and spheres and compare them to what is observed on a flat surface. Then, we study the effect of substrate motion. We make impacts on soft materials that can be deformed by the drop. We show that this situation can lead to fast bouncing and interpret the contact time as the result of an interplay between the timescale of the drop and that of the substrate. We also discuss the influence of substrate deformation on splashing. We go deeper into the effect of substrate motion by using rigid materials which movement we can trigger. We evidence new liquid shapes, conical cavities, by submitting a drop, initially at rest, to a vertical impulse.Surprisingly, the low, but present, adhesion of superhydrophobic materials is the key ingredient needed to observe such shapes. We also work on the effect of motion at the onset of impact, by trigerring the substrate movement using the signal from a MEMS force sensor intregrated in the surface. This setup allow us to reach contact times that represent 20% of the contact time on an immobile substrate. Finally, we change perspective and modify the liquid instead of the solid. We show that viscous drops can bounce as long as their viscosity does not exceed 200 times that of water.
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Pierre Chantelot. Rebonds spéciaux de liquides. Mécanique des fluides [physics.class-ph]. Université Paris-Saclay, 2018. Français. ⟨NNT : 2018SACLX120⟩. ⟨tel-02011789⟩

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