Context

Fascinated by the beauty of water rolling off a lotus leaf, a team of chemical engineers has now created a similar superhydrophobic coating that can be used to save steel from rusting.

About

• A nano scopic coating whose main function is to protect the surface from the water and repel it is called super hydrophobic coatings.
• In recent times, many super hydrophobic surfaces have captured the attention of scientists and they have extended their researches on those surfaces in order to obtain the same material which can be used to repel any type of liquid.

Important features:

• Superhydrophobic coatings have a lot of practical applications where it protects the coated equipment or material from corrosion, contamination prevention and protection from other hazardous chemicals.
• The water repellency of the surface is the important factor to be considered here because a super hydrophobic surface is that surface whose water contact angle is more than 150 degrees.
• There are plenty of super hydrophobic surfaces in nature, including lotus leaves, butterfly wings, duck feathers, etc.
• Inspired by nature, super hydrophobic surfaces can be derived by employing two approaches.
  • In the first approach, the solid surface is chemically enhanced with a low-surface material.
  • In the second approach, nano and micro-scale structures are created on the layer to stop water from completely being in contact with the surface.

The study:

• The team from the Indian Institute of Technology (Indian School of Mines), Dhanbad, and Ohio State University used polyurethane and silicon dioxide nanoparticles to create the coating which can be easily spin-coated on steel.
• The work is published in the journal Philosophical Transactions of the Royal Society A.

How they did it?

• Before applying the coating, the team created a roughness on the steel using a chemical etching process to improve the adhesion strength. Without this, the coating tends to easily peal off due to smoothness of steel.
• The team also tried different methods for the application of the coat on steel and found that spin coating was advantageous and cost-effective compared to immersion coating and spray coating.
• Spin coating dried quickly and the thickness of the coat could be controlled easily.
• The surface of the coating was found to have super hydrophobic
• The coating was also chemically stable in both acidic (pH 5) and alkaline (pH 8) conditions for more than six weeks. It also exhibited thermal stability up to 230 degree C.
• The mechanical stability of the coating was tested with water jet, floating, bending, sand abrasion tests and was found to be highly stable.
• Not just steel, the coating can be done on other metallic surfaces, such as aluminum, copper, brass.
• The team have also successfully developed super hydrophobic coatings for glass, cloth, paper and wood.
• Self-cleaning: Another useful property exhibited by the coating was of self-cleaning. When water droplets were made to fall on an uncoated surface they stuck to it and made a messy surface.
  • However, in the case of a coated sample, water droplets roll away while collecting dust from the surface.