superhydrophobic-coating-on-metallic-surfaces

Why in News

  • A team from the Indian Institute of Technology (Indian School of Mines), Dhanbad, and Ohio State University has created a superhydrophobic coating to save steel from rusting.
  • The coating was made from polyurethane and silicon dioxide nanoparticles.

Superhydrophobic Surfaces

  • The term hydrophobicity is derived from two greek words that are hydro (water) and phobos (fear). It is the ability to repel water.
  • Superhydrophobic coating is a nanoscopic surface layer that repels water.
  • Adding a superhydrophobic coating makes a surface liquid and water repellent, easy to clean, and boosts its anti-icing performance (ability to delay the formation of ice for a certain period of time)
  • Super-hydrophobic coatings are also found in nature; they appear on plant leaves, such as the Lotus leaf, and some insect wings.
  • Apart from steel the coating can be done on other metallic surfaces, such as aluminum, copper, brass. The coatings have also been developed for glass, cloth, paper and wood.
  • Developing an antimicrobial superhydrophobic coating for biomedical applications is also being worked on.
  • Without this, the coating tends to easily peel off due to smoothness of steel.
  • The spin coating was found to be more 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

Silicon dioxide

  • Silicon dioxide (SiO2), also known as silica, is a natural compound made of two of the earth's most abundant materials: silicon (Si) and oxygen (O2).
  • Silicon dioxide is most often recognized in the form of quartz. It's found naturally in water, plants, animals, and the earth.

Polyurethane

  • Polyurethane is a polymer composed of organic units joined by urethane links.
  • It is a plastic material, which exists in various forms.
  • They are used in a wide variety of applications to create all manner of consumer and industrial products that play a crucial role in making our lives more convenient, comfortable and environmentally friendly.

Properties of the Coating

  • Chemically Stability: Stable in both acidic (pH 5) and alkaline (pH 8) conditions for more than six weeks.
  • Thermal Stability: Stable up to 230 degree C.
  • Mechanical Stability: Highly stable when tested with water jet, floating, bending, sand abrasion tests.
  • 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.
  • Easy to make
     
    • The chemicals used to make the coating are easily available and are also environmentally friendly.
    • The cost of coating will further reduce when mass-produced on commercial scale.

Source: TH