Superhydrophobic and superoleophobic properties in nature

Abstract

In this review, we report on superhydrophobic and superoleophobic properties found in nature, which are strongly expected to benefit various potential applications. Mimicry of nature is the easiest way to reproduce such properties because nature has for millennia produced plants, insects and animals able to repel water as well as low surface tension liquids such as oils. The most famous example is the lotus leaf, but we may also consider insects able to walk on vertical surfaces or on the water surface , insects with colored structured wings or insects with antifogging and anti-reflective eyes. Most of the time, nature produces nanostructured waxes to obtain superhydrophobic properties. Very recently, the repellency of oils has been reported in springtails, for example. While several publications have reported the fabrication of superoleophobic surfaces using re-entrant geometry, in all of these publications fluorinated compounds were used because they have high hydrophobic properties but also relatively important oleophobic properties in comparison to hydrocarbon analogs even if they are intrinsically oleophilic. However, nature is not able to synthesize fluorinated compounds. In the case of the springtails, the surface structures consists of regular patterns with negative overhangs. The chemical composition of the cuticles is composed of three different layers: an inner cuticle layer made of a lamellar chitin skeleton with numerous pore channels, an epicuticular structures made of structural proteins such glycine (more than 50%), tyrosine and serine an the topmost envelope composed of lipids such as hydrocarbon acids and esters, steroids and terpenes. This discovery will help the scientific community to create superoleophobic materials without the use of fluorinated compounds.