Applications of super hydrophobic coatings

Due to the extreme repellence and in some cases bacterial resistance of hydrophobic coatings, there is much enthusiasm for their wide potential uses with surgical tools, medical equipment, textiles, and all sorts of surfaces and substrates. However, the current state of the art for this technology is hindered in terms of the weak durability of the coating making it unsuitable for most applications. Newer engineered surface textures on stainless steel are extremely durable and permanently hydrophobic. Optically these surfaces appear as a smooth matte surface but microscopically they consist of rounded depressions one to two microns deep over 25% to 50% of the surface. These surfaces are produced for buildings which will never need cleaning.

Super hydrophobic surfaces have attracted the interest of scientists and engineers for both fundamental research and their practical applications, such as contamination prevention, self-cleaning, antifouling surface designs, anti-icing coatings, corrosion resistance of metals and their alloys, and biomedical and biological applications, among others. Coatings with hydrophobic surfaces can be fabricated by controlling their topographic features and surface energies.

There are many non-chemical companies on the Internet offering super hydrophobic coatings for all sorts of unsuitable things, but it is important to understand the science of these coatings before attempting to use this technology:

Instead of using fluorine atoms for repellence like many successful hydrophobic penetrating sealers (not super hydrophobic), superhydrophobic products are a coating—they work by creating a micro- or nano-sized structure on a surface which has super-repellent properties.

These very tiny structures are by their nature very delicate and very easily damaged by wear, cleaning or any sort of friction—this cannot be disputed—if the structure is damaged even slightly it loses its superhydrophobic properties. This technology is based on the microstructure of hairs on a lily pad which makes water just roll off. Rub a lily leaf a little and it will no longer be superhydrophobic, plus unlike a lily leaf which can heal and grow new hairs, a coating will not do this.

As a result, unless advancements can resolve the identified weakness of this technology its applications are limited. It is used mainly in sealed environments which are not exposed to wear or cleaning, such as electronic components (like the inside of smart phones) and air conditioning heat transfer fins, to protect from moisture and prevent corrosion.

Surfaces can be made hydrophobic without the use of coating through the altering of their surface microscopic contours, as well. The basis of hydrophobicity is the creation of recessed areas on a surface whose wetting expends more energy than bridging the recesses expends. This so called Wenzel-effect surface or lotus effect surface has less contact area by an amount proportional to the recessed area, giving it a high contact angle. The recessed surface has a proportionately diminished attraction foreign liquids or solids and permanently stays cleaner. This has been effectively used for roofs and curtain walls of structures that benefit from low or no maintenance

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