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The Birth of Superhydrophobic Composite Coating

Research and development background of anti – fog transparent coating

From eyeglasses to camera lenses to car windshields, transparent materials have been used in almost every aspect of life. The problem with these transparent materials, which are widely used in daily life, is that they are prone to fog. For example, in the winter, wearing glasses from the outside into the room, always on the glasses fog blocking the line of sight, which has been a problem for many people.
Nowadays, there are many anti-fog strategies for transparent materials. The most commonly used one is to modify the surface of transparent lenses with hydrophilic coating, so that the water condensed on the transparent coating forms a water film instead of a water bead, thus acting as an anti-fog effect. However, the antifouling performance of the hydrophilic lens is decreased due to its large surface energy. In order to ensure that transparent materials are anti-fog and anti-pollution, some researchers have developed a kind of heterogeneous transparent coating by covering the hydrophilic coating with a layer of hydrophobic nanomaterials. When water vapor will condense on the transparent coating, water molecules can be absorbed by the hydrophilic coating through the hydrophobic nanometer layer to ensure the surface without fog, while the hydrophobic nanometer layer can play a good anti-pollution effect. Although this method is very effective, but once the hydrophilic coating reaches saturation, it will lead to the failure of anti-fog function.

Superhydrophobic Composite Coating

Hyomin Lee's team at Posco has developed a new water-absorbing superhydrophobic composite coating. The coating consists mainly of hydrophilic polymer composite substrate and hydrophobic polymer column array. The base material of the coating is chitosan and carboxymethyl cellulose, which has strong electrostatic attraction between the two materials, making the base material bond closely. Chitosan and carboxymethyl cellulose has a good hydrophilic, can be used as a coating absorbent material. A layer of silica nanoparticles is coated on a water-absorbing polymer coating. Finally, columnar fluoropolyethers were attached to the silica nanoparticle layer to achieve the purpose of hydrophobic antifouling. The nanostructured coating is transparent and can be used to prevent fog and pollution.
Column fluoropolyether arrays were attached to the polymer/nanometer silica coating surface by the template method to form a hydrophobic surface. The nanometer silica layer ensures the tight binding of the fluoropolymere-containing nanocrystals to the substrate coating, while the distributed fluorine-containing nanocrystals make the composite coating more hydrophobic, while the columnar nanocrystals do not prevent the substrate from absorbing moisture during the condensation of water vapor on the coating surface. Thus, while ensuring the surface of the hydrophobic surface, the substrate material can absorb water vapor smoothly to ensure no condensation of water droplets on the surface of the coating. Due to the self-lubricating effect of the fluorinated material, the columnar array can also act as a scratch-proof material. After sandpaper polishing thickness, the polymer/silica coating without the column fluoropolyether array has obvious scratches.
Through the design of the coating structure, the researchers developed a transparent coating with hydrophilic polymer substrate and hydrophobic nanocrystal array, which perfectly combined the hydrophilic and hydrophobic materials with opposite properties to realize the anti-fouling and anti-fog function of the coating. The work is published in Advanced Material as "Wet Style Superhydrophobic Antifogging, for Optical Sensors".

Application Prospect

In today's world of glass and ceramics, the scope of the invention is immense. It is believed that the results of this research will soon be used on a large scale.

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