Abstract
It has been recently shown that the presence of macrotextures on superhydrophobic materials can markedly modify the dynamics of water impacting them, and in particular significantly reduce the contact time of bouncing drops, compared with what is observed on a flat surface. This finding constitutes a significant step in the maximization of water repellency, since it enables to minimize even further the contact between solid and liquid. It also opens a new axis of research on the design of super-structures to induce specific functions such as anti-freezing, liquid fragmentation and/or recomposition, guiding, trapping and so on. Here we show that the contact time of drops bouncing on a repellent macrotexture takes discrete values when varying the impact speed. This allows us to propose a quantitative analysis of the reduction of contact time and thus to understand how and why macrotextures can control the dynamical properties of bouncing drops.
Highlights
It has been recently shown that the presence of macrotextures on superhydrophobic materials can markedly modify the dynamics of water impacting them, and in particular significantly reduce the contact time of bouncing drops, compared with what is observed on a flat surface
Impact is affected by the presence of large defects: submillimetre ridges[3], big conical posts[4] or large chemical defects[21] on a water-repellent material markedly modify the bouncing dynamics by reshaping the liquid at impact and takeoff, which can reduce by a large amount the contact time of rebounding droplets[3,4]
Bird et al recently showed that ridges can divide by a factor of order 2 the contact time t of bouncing drops[3], and we investigate how this reduction varies with impact velocity V, drop size and macrotexture radius, which leads to a scenario for understanding the effect
Summary
It has been recently shown that the presence of macrotextures on superhydrophobic materials can markedly modify the dynamics of water impacting them, and in particular significantly reduce the contact time of bouncing drops, compared with what is observed on a flat surface. This finding constitutes a significant step in the maximization of water repellency, since it enables to minimize even further the contact between solid and liquid. Extensions to other designs of the macrotexture are shown to provide other shapes at impact, and other contact times
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