Self-Cleaning Glass

Additional Details

Self-cleaning glass is a specific type of glass with a surface which keeps itself free of dirt and grime through photocatalytic decomposition. A nanometer-scale coating of titanium dioxide on the outer surface of the glass introduces two mechanisms which give it the self-cleaning property. Harsh chemicals that are used to clean normal glass are usually washed off into the soil and contaminate it. The use of self cleaning glass eliminates this environmental hazard. 

Dual Process 

Self cleaning glass cleans itself in two stages. The first stage is called photo-catalysis which is the action of light on the surface of the glass to basically chomp away or eat the dirt on the surface. The next is a process known as hydrophilicity. This basically ensures that any water that falls on the surface forms sheets and washes away dirt uniformly. The glass spreads the water evenly over its surface, without forming droplets. 

Self Cleaning Glass has a coating of titanium dioxide on its outer surface. Titanium dioxide is an inorganic pigment which is widely used in a several products: everything from sunscreen where it reflects away some of the sun’s UV rays through to toothpaste through to the whitener responsible for the white colour in white paint or even in paper. 

Titanium dioxide is present as a very thin coating on the outside surface of the glass. It has a thickness of about 25mm. The action of sunlight on the titanium dioxide generates a species known as electrons and holes. These electrons and holes, along with a specific property of titanium dioxide migrate to the surface and start a process known as oxidation of any organic material which is present. Effectively, the titanium dioxide absorbs the UV component of sunlight and causes the degradation and break-down of any organic material, dust or debris which are on the surface of the glass - It converts them into carbon dioxide and water. One of the best features of this is that it works on the bottom of the dirt outwards and so loosens the dirt on the material coating by destroying the contact layer of the dirt and the glass.

Any rain water impacting the surface will form a very smooth sheet which washes down foreign particles uniformly. This happens through the action of sunlight on titanium that produces a surface which is highly hydrophilic, or water-loving. Water loves wetting the surface and the action of sunlight generates hydroxyl species on the surface effectively. 

Everything that settles on self cleaning glass is washed down at the same rate, but this property primarily works on surfaces which have some form of slant. If the surface is perfectly horizontal then it would struggle because of a lack of gradient for the water to run off.

Only a small amount of sunlight is required to activate the coating, which ensures that self-cleaning property will function even on cloudy days.  A simple rinse with water during dry spells will help keep the surface clean.