A nano coating or hydrophobic coating is a surface layer that repels water. It is made from a superhydrophobic (ultra-hydrophobicity) material. In industry, nano coatings are used in surface applications, often functioning as a water and dirt repellent e.g. coatings for cars. In addition to automotive, practical applications exist in food processing, interiors and textiles. Super-hydrophobic coatings can also found in nature.
What is a nano coating (hydrophobic coating)?
Hydrophobic coatings are built from a delicate nano structure. Abrasion can alter the fine structure. These ceramic coatings are mostly used in the fabrication of electronic components. A nano coating has the potential to prevent scratch resistance and even be anti-bacterial.
The silica-based coatings are the most cost effective to use and can be easily applied via an industrial spray mechanism. Oxide polystyrene composites are more durable but the method is very expensive. Carbon nano-tubes are also a costly, intensive process.
Bases used in nano coatings
Superhydrophobic coatings utilise the following bases:
- Manganese oxide polystyrene
- Zinc oxide polystyrene
- Carbon nano-tubes
- Silica nano-coating
- Fluorinated silanes
Advantages of nano coatings
They can be eco-friendly, anti-corrosive and UV resistant. Nano coatings can actively self-clean. In addition to their water repellency, they can also be manufactured to be oleo phobic.
Industrial applications of nano coatings
Superhydrophobic coatings have important applications in the maritime industry. Drag reduction for a ships hull can theoretically lead to an increased fuel efficiency. They can also reduce corrosion and prevent marine organisms from growing on the hull.
They have potential uses in vehicle windshields. Superhydrophobic coatings also have the ability to harvest other minerals from seawater brine. Safety for the environment and for workers is a big issue and The International Maritime Organisation has strict policies about keeping water safe from potentially dangerous additives.
Due to their bacterial resistance, there are potential uses within medical equipment and textiles. However, the weak durability is often the limiting factor.
- Utilising fluorine atoms for repellence in hydrophobic sealers, they can work by creating nano structure on the surface which has repellent properties.
- It is used mainly in sealed environments which are not exposed to wear or cleaning, such as electronic components e.g. smart phones and air conditioning heat transfer fins.
Fundamentally, hydrophobicity is the creation of recessed areas whose wetting expends more energy than bridging the recesses expends. This Wenzel-effect surface has less contact area proportional to the recessed area, leading to a high contact angle.
The contact angle (nano materials)
The contact angle quantifies the ability of a liquid to wet the surface of a solid. The angle follows the surface tension of the fluid and the nature of the substrate. At the boundary between droplets and the gaseous environment, the surface tension causes a contour. At the edge of the drop, where the contour merges into the surface, the angle between the interface liquid, solid and the tangent to the interface liquid and gaseous forms.
If the liquid is uniformly moving across the solid surface, this is complete wetting, identified with a contact angle of 0 °. Between 0 ° and 90 °, the surface is considered wettable or hydrophilic. An angle of 90 ° to 180 ° results in a hydrophobic surface. If the angle nears 180 °, it is classed as an ultra-hydrophobic surface.
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