How is Self cleaning Properties on Glass, ACP & other materials Achieved

Self Cleaning Materials becoming the new trend in the façade industries. Now a days we hear lot about transparent liquid which when applied to the surface, like glass, acp, aluminium sheets and various external façade materials, makes the Self cleaning. This nature also known as” Lotus effect” where water on the leaves of Lotus plant rolled down. These leaves had a combination of surface roughness & water repellent wax crystals givng it super hydrophobic properties.

Many companies like 3m, Alcoa, Active, BASF, Corning, Ford, Nippon, and PPG are investing into research of the long term technology where any material would have self cleaning properties.

The growing interest in self cleaning coatings technologies is due to their high potential in reducing maintenance cost of the window & façade.

Two type of Self Cleaning Properties

  • Hydrophobic
  • Hydrophilic

Hydrophobic

These have high water angles above 90 degrees. Self cleaning has water angles of more than 150 degrees know as super hydrophobic. Nature also has “Lotus Effect” where water droplets can be seen on Lotus leaf due to its hydrophobic properties. These surfaces are highly water repellent & water roll down into spherical droplets carrying the dust also.

A super hydrophobic surface is obtained if hydrophobic surface is roughened on a micro or nano scale. Thus efficiency of self cleaning coating is dependent on roughness & chemical composition on the surface & dust particle adhesion to water droplet.

Hydrophilic            

These self cleaning coatings are based on photcatalysis, i.e. when exposed to Light they are able to break down impurities. Titanium Dioxide is well know hydrophilic self cleaning coating due to its physical & chemical properties. It is non toxic, chemically inert when there is no light present, inexpensive, easy to handle.

The strong oxidation power & super hydrophilic properties of Tio2 makes it good material used for outdoor. Just see illustration how Tio2 drives the dust away.

. 1. When UV light shines on Tio2 electrons negative charges releases.

  1. Electorns interact with water (H2O) breaking them to hydroxyl(OH) which are reactive.

  1. These agile hydroxyl radicals attack the hefty organic (carbon-based) molecules from which most          dirt is made, breaking apart their chemical bonds and turning them into smaller, harmless substances such as carbon dioxide and water. This is an example of oxidation.

  1. The hydroxyl radicals also make the glass hydrophilic (water-loving). When it rains, water molecules spread evenly across it and wipe it clean like a kind of automatic squeegee!

 

Ultra Violet Light + TiO2 can be used in following areas

 

Advantages

  •  Self Cleaning Window looks neat for Life time.
  • Less maintenance of Window & Façade cleaning.
  • Less Water Consumption for cleaning.

 

Disadvantages

  • 15 to 20% More Cost of the Glass.
  • Reliability of TiO2 systems on Sunlight & Rains.
  • Cleaning with abrasive materials might damage the coatings.
  • Inside cleaning has to be done manually.

 

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