Natural superhydrophobic surfaces water contact angles

Superhydrophobic surfaces (water contact angles higher than 150°) can only be achieved by a combination of hydrophobicity (low surface energy materials) with appropriate surface texture. In nature one can find an array of impressive and elegant examples of superhydrophobic surfaces. For example, on a lotus leaf rain drops bounce off after impact, then entirely roil off the lotus leaf and drag along any dirt particles, without leaving residues. 

The fact that tuning the chemical nature alone of the soUd is unable to provide friction reduction beyond the submicrometer scale has led to the suggestion that one should try to get rid of the actual solid-liquid boundary by coating the surface with a bubble (a gas layer). Such a situation, where gas is trapped at the solid interface and partially replaces the solid-liquid contact, can be achieved in specific conditions (see Section 2.1) with the use of the so-called superhydrophobic surfaces. Such surfaces, which combine surface roughness and nonwettability to achieve unique static properties with water contact angles close to 180°, were indeed recently predicted [17] to exhibit also super-lubricating characteristics. 

Natural superhydrophobic surfaces [1, 2] as observed with leaves of some plants or feathers of some birds, correspond to hydrophobic surfaces whose water contact angle (0) is higher than 150° [3], Such surfaces are sometimes called self-cleaning surfaces since a water droplets will take up the dirt particles and roll off the surface [2], The values of water contact angles cannot be obtained with real surfaces, as... 

By modifying the surfaces or choosing appropriate polyelectrolytes, both superhydrophobic (contact angle 150°)" " and superhydrophilic 6<5° in less than 0.5 sec)" surfaces can be created. In nature, there are matty superhydrophobic surfaces, such as the sacred lotus leaf, taro leaf, grass leaf and water strider s legs. The superhydrophobicity of these materials is mostly related to the hierarchical roughness, voids, channels and hydrophobic structure of the suifaces." Thus, superhydrophobic surfaces may be used for self-cleaning purposes on A1 alloy surfaces, which in turn reduces corrosion rates. 

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