Superhydrophobic states (original) (raw)

Nature Materials volume 2, pages 457–460 (2003) Cite this article

Abstract

It is well known that the roughness of a hydrophobic solid enhances its hydrophobicity1,2,3,4,5,6,7,8,9,10. The contact angle of water on such flat solids is typically of the order of 100 to 120°, but reaches values as high as 160 to 175° if they are rough3,4,5 or microtextured6,7,9,10. This result is remarkable because such behaviour cannot be generated by surface chemistry alone. Two distinct hypotheses are classically proposed to explain this effect. On one hand, roughness increases the surface area of the solid, which geometrically enhances hydrophobicity (Wenzel model)1. On the other hand, air can remain trapped below the drop, which also leads to a superhydrophobic behaviour, because the drop sits partially on air (Cassie model)2. However, it is shown here that both situations are very different from their adhesive properties, because Wenzel drops are found to be highly pinned. In addition, irreversible transitions can be induced between Cassie and Wenzel states, with a loss of the anti-adhesive properties generally associated with superhydrophobicity.

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Figure 1: The two models of superhydrophobicity.

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Figure 2: Compression of a millimetric water drop between two identical microtextured hydrophobic surfaces.

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Figure 3: Separation of the two plates after having imposed a pressure Δ_P_ of about 250 Pa.

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Acknowledgements

We thank Steve Abbott and Nigel Holmes for kindly providing the samples, José Bico, Cédric Dieleman, Harald Keller, Neelesh Patankar and Uwe Thiele for fruitful discussions, and BASF for their support.

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  1. Laboratoire de Physique de la Matière Condensée, UMR 7125 du CNRS, Collège de France, Paris, 75231 Cedex 05, France
    Aurélie Lafuma & David Quéré

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  1. Aurélie Lafuma
  2. David Quéré

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Correspondence toDavid Quéré.

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Lafuma, A., Quéré, D. Superhydrophobic states.Nature Mater 2, 457–460 (2003). https://doi.org/10.1038/nmat924

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