Self-cleaning glass

Self-cleaning glass is a specific type of glass with surface which keeps itself free of dirt and grime through natural processes.

The first self-cleaning glass was based on thin film titanium dioxide coating. The glass cleans itself in two stages. The "photocatalytic" stage of the process breaks down the organic dirt on the glass using ultraviolet light in sunlight (even on overcast days) and makes the glass hydrophilic (normally glass is hydrophobic). During the following "hydrophilic" stage rain washes away the dirt, leaving almost no streaks, because hydrophilic glass spreads the water evenly over its surface. [http://news.bbc.co.uk/2/hi/technology/3770353.stm BBC News] , 8 June 2004] .

Titanium dioxide is a material of choice because it is characterized by high photocalytic properties, chemical stability and low price. Its anatase phase is most photocalytic. What is more, under the UV irradiation its surface structure changes to generate OH groups, making it superhydrophilic. [ SUmio Sakka (ed.) (2005) "Handbook of Sol-Gel Science and Technology Processing Characterization and Applications", [http://books.google.com/books?id=QTCyQoTVZWkC&pg=PA385&lpg=PA385&dq=%22sol-gel%22+%22self-cleaning+glass%22&source=web&ots=Rp4oyipTPD&sig=brnjh6hjbQDRs-JKuqAE7sXB3HM#PPA385,M1 Chapter 18, "Coatings with Photocatalyst on Architectural Glass"] . ISBN 1402079680.]

It is speculated that other possible application areas are computer monitors and PDA screens, where fingerprints are undesirable. [ [http://www.engadget.com/2004/06/04/self-cleaning-glass/ "Self-cleaning glass"] , "Engadget," June 4, 2004.]

Titanium dioxide–based glass cannot decompose thick non-transparent deposits, such as paint or silicone, waterstop fingerprints or bleeding after weathering, or stucco dust produced during construction.

Another approach to self-cleaning glass is suggested basing on the hydrophobic "lotus effect". [ [http://www.sciencedaily.com/releases/2005/01/050125085826.htm "'Bumpy' Glass Could Lead To Self-cleaning Windows, Slick Micromachines"] , "Science Daily", January 28, 2005.]

Since 2001 the TC24 "Coatings on Glass" committee International Commission on Glass has been trying to set up test methods for evaluation of photocatalytic self-cleaning coatings on glass. [ [http://www.icg.group.shef.ac.uk/tc24.html#Index TC24 reports] ]

Brands

* The Pilkington Activ brand by Pilkington is claimed by the company to be the first self-cleaning glass. [ [http://www.pilkingtonselfcleaningglass.co.uk/ Pilkington Glass Manufacturers] ] It uses the 15 nm thick transparent coating of microcrystalline titanium dioxide. The coating is applied by chemical vapor deposition"A comparative study of three techniques for determining photocatalytic activity", Journal of Photochemistry and Photobiology A: Chemistry, Volume 188, Issues 2–3, 2007, Pages 387–391. doi|10.1016/j.jphotochem.2006.12.040]
* The SunClean brand by PPG Industries also uses the coating of titanium dioxide applied by a patented process. [ [http://corporateportal.ppg.com/NA/Glass/ResidentialGlass/Homeowners/ProductInformation/SunClean/SunCleanHowItWorks.htm SunClean glass info] ]
* Neat Glass by Cardinal Glass Industries has the <10nm titanium dioxide layer applied by magnetron sputtering [http://www.cardinalcorp.com/data/tsb/cg/CG05.pdf Neat Glass] , Cardinal CG Technical Service Bulletin # CG05-06/06.]
* SGG Aquaclean (1st generation, hydrophylic only, 2002 [ [http://www.theglazine.com/newsarchive/news271101.html "Saint Gobain launches self-cleaning glass"] ] ) and Bioclean (2nd generation, both photoctive and hydrophilic, 2003 [ [http://www.saint-gobain.co.uk/main.asp?nid=37 Saint-Gobain Glass launches 2nd generation self-cleaning glass] ] ) by Saint-Gobain. [ [http://www.selfcleaningglass.com/technical-support.asp SGG Bioclean technical info] ] The Bioclean coating is applied by chemical vapor deposition.

ee also

*ETFE films, transparent polymer films described as self-cleaning

References