On hydrophobic surfaces, surface textures are generated, which typically look like this:
Cross section of textures at the surface of superhydrophobic surfaces.
Water is sitting at the top of the posts, so the contact area between the drop and the surface is effectively reduced by a factor Φ called the surface fraction.
The real wetted area is s. The apparent wetted area is S. The surface fraction is Φ=s/S.
A solid surface is superhydrophobic when a water drop sitting on the surface exhibits a very large contact angle, typically larger than 150°. In (…)
Here is a flat surface on which drops always go in the same direction. Instead of spreading evenly they spread only in one and the same (…)
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