SuperHydrophobic Coating: Ways to turn surfaces super hydrophobic with coating

Recently there is a great interest in the development of super-hydrophobicity on a wide variety of surfaces. Water is mainly responsible for corrosion problems on most of the materials. The maintenance of e.g. concrete constructions from corrosion caused by the water, costs million $/ year. So a superhydrophobic coating would significantly prevent the materials from corrosion.

Inspired by the “lotus-leaf effect” a lot of techniques have been developed to create super-hydrophobic surfaces. The aim of the scientists is to create a coating with a surface morphology that mimics the morphology of the lotus-leaf. Some of the developed methodologies are: Coating of substrates with various nanoparticles mixed with polymers, electrochemical deposition of gold and silver aggregates followed by chemisorption of a monolayer of n-dodecanothiol, electrodeposition of copper combined with lithography or copper wet etching, close-packed polystyrene microsphere topography, casting of polymer solutions under humid conditions, replication of the lotus-leaf structure in PDMS by nanocasting, mechanical assembly of monolayers on elastomeric surfaces and a gelation process for polypropylene and tetraethyl orthosilicate mixed with an acrylic polymer.

Plasma techniques have also been used either to modify the chemistry and the surface morphology of polymeric surfaces, such as polybutadiene and polypropylene to deposit ribbon like randomly distributed microstructures, or to etch an inhomogeneous material. Some methods for the production of super-hydrophobic surfaces have been also based on the formation of densely packed high-aspect-ratio structures such as polymer nanofibres, aligned carbon nanotubes, Si pillars fabricated by photolithography and plasma etching, and Si nano-rod arrays fabricated by Si vapour deposition.

Most of the developed methodologies have been tested only in lab conditions and not outdoor.

Figure: Water droplet on calcium carbonate treated with a perfluorinated polymer and silica nanoparticles

Pros and Cons of Today’s Super-Hydrophobic Coatings Technologies.

Superhydrophobic coatings technologies are in fact under development. Most of the methodologies have been tested only in the lab. This is the major disadvantage. The behaviour of these coatings at outdoor condition has not been tested. It is also known that it is very difficult to produce robust super-hydrophobic coatings. The surface morphology is in general sensitive to mechanical wear. Finally most of the methodologies demand expensive materials, special knowledge, or some special equipment and can not be applied on all the materials. A simple methodology demanding materials of low-cost, with good results is the one with the polymers and the nanoparticles.

The advantages of the Super-Hydrophobic Coatings Technologies come from their properties and their potential applications. Self-cleaning glasses, clothes etc, protection against corrosion of all the concrete constructions (e.g bridges, marines, under water constructions etc), anti-snow sticking, even monument protection are only some of them.