Self-cleaning glass
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Self-cleaning_glass".

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

The first self-cleaning glass was based on a 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.¹.

Titanium dioxide is a material of choice because it is characterized by high photocatalytic properties, chemical stability and low price. Its anatase phase is most photocatalytic. What is more, under the UV irradiation its surface structure changes to generate OH groups, making it superhydrophilic.²

It is speculated that other possible application areas are computer monitors and PDA screens, where fingerprints are undesirable.³

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.⁴

Another approach to self-cleaning glass has been suggested, based on the hydrophobic "lotus effect". ⁵

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.⁶

Brands

• The Pilkington Activ brand by Pilkington is claimed by the company to be the first self-cleaning glass.⁷ It uses the 15 nm thick transparent coating of microcrystalline titanium dioxide.¹ The coating is applied by chemical vapor deposition⁸
• The SunClean brand by PPG Industries also uses a coating of titanium dioxide, applied by a patented process. ⁹
• Neat Glass by Cardinal Glass Industries has a titanium dioxide layer less than 10 nm thick applied by magnetron sputtering⁴
• SGG Aquaclean (1st generation, hydrophilic only, 2002¹⁰) and Bioclean (2nd generation, both photoactive and hydrophilic, 2003¹¹) by Saint-Gobain.¹² The Bioclean coating is applied by chemical vapor deposition.⁸

See also

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

References