Thèse de doctorat en Physique des liquides
Sous la direction de David Quéré.
Soutenue en 2015
This work focuses on situations in which movement and liquid repellency are combined. First, we study dynamic hydrophobicity, a phenomenon created by the horizontal movement of a flat surface, here a rotating plate of bare aluminum. When the surface reaches a critical velocity, approaching droplets cannot penetrate the boundary layer of air that covers the surface, thus protected from wetting. Droplets that are gently deposited on the substrate levitate a few micrometers above the surface, while falling droplets can bounce off, much faster than in other non-wetting situations. If the plate moves fast enough, all liquids can be repelled, creating an omniphobic surface. In a second part, we investigate the dynamics of drops in contact with surfaces textured at a microscopic scale, which makes them water-repellent. We show that viscous drops deposited on a moving superhydrophobic surface are not immediately carried away, but accelerate and start to spin very rapidly. As the substrate velocity increases, the spinning makes the drops loose their spherical shape and turn into bilobes, and sometimes trilobes. We also study the impact of water droplets on superhydrophobic surfaces macrotextured by a straight wire or a marble of same repellency, with a typical size of 100 mm. The bouncing dynamics are dramatically modified in presence of the macrotexture : on a wire drops take-off as 1, 2 or 4 independent sub-units while in presence of a marble they exhibit surprising doughnut shapes. This affects the contact time, which takes discrete values with increasing impact velocity. At high velocity it is divided by a factor of 2 compared to a non-textured surface, which enhances anti-icing properties.
Dynamic hydrophobicity and hydrophobic dynamics
Pas de résumé disponible.