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Issue 23, 2015
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Two types of Cassie-to-Wenzel wetting transitions on superhydrophobic surfaces during drop impact

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Abstract

Despite the fact that superhydrophobic surfaces possess useful and unique properties, their practical application has remained limited by durability issues. Among those, the wetting transition, whereby a surface gets impregnated by the liquid and permanently loses its superhydrophobicity, certainly constitutes the most limiting aspect under many realistic conditions. In this study, we revisit this so-called Cassie-to-Wenzel transition (CWT) under the broadly encountered situation of liquid drop impact. Using model hydrophobic micropillar surfaces of various geometrical characteristics and high speed imaging, we identify that CWT can occur through different mechanisms, and at different impact stages. At early impact stages, right after contact, CWT occurs through the well established dynamic pressure scenario of which we provide here a fully quantitative description. Comparing the critical wetting pressure of surfaces and the theoretical pressure distribution inside the liquid drop, we provide not only the CWT threshold but also the hardly reported wetted area which directly affects the surface spoiling. At a later stage, we report for the first time to our knowledge, a new CWT which occurs during the drop recoil toward bouncing. With the help of numerical simulations, we discuss the mechanism underlying this new transition and provide a simple model based on impulse conservation which successfully captures the transition threshold. By shedding light on the complex interaction between impacting water drops and surface structures, the present study will facilitate designing superhydrophobic surfaces with a desirable wetting state during drop impact.

Graphical abstract: Two types of Cassie-to-Wenzel wetting transitions on superhydrophobic surfaces during drop impact

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Publication details

The article was received on 08 Apr 2015, accepted on 01 May 2015 and first published on 01 May 2015


Article type: Paper
DOI: 10.1039/C5SM00825E
Author version available: Download Author version (PDF)
Citation: Soft Matter, 2015,11, 4592-4599
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    Two types of Cassie-to-Wenzel wetting transitions on superhydrophobic surfaces during drop impact

    C. Lee, Y. Nam, H. Lastakowski, J. I. Hur, S. Shin, A. Biance, C. Pirat, C. “CJ” Kim and C. Ybert, Soft Matter, 2015, 11, 4592
    DOI: 10.1039/C5SM00825E

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