Question of the Week

How is self cleaning glass made?

Sat, 20th Sep 2014

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Nikki Way asked:

Hello I am a year 12 Student at Salisbury High School and I am doing an assignment on Nanotechnology, self-cleaning glass. I have a question: "How is self cleaning glass made?"


It will be greatly appreciated if you can possibly provide any information.


Thank-You from Nikki



There are two types of self cleaning glass. The more common one makes use of titanium dioxide nanoparticles that are deposited on the surface.  They are not simple pieces of glass, as they are covered in an ultra-thin coating, a layer roughly 10–25 nanometers thick. To put that into perspective, that’s about 1000 times thinner than a piece of human hair. The organic dirt that settles on these surfaces is broken down by UV light with the help of these particles. In this way the sun effectively burns away the dirt, but since UV light is required, this works best outdoors and is therefore not ideal for smartphones.

The second effect uses an applied substance that strongly repels water.  The resulting surface is super-hydrophobic – water-hating - so repels nearly any substance that it comes into contact with. Any type of dirt is easily removed, by simply rinsing the surface with water, for example in a rain shower. Strictly speaking, this surface is not self-cleaning since it requires water and should therefore rather be termed "easy clean surface”.  This is still in development and might well be a solution to prevent fingerprints on smartphones in the future, particularly because some of these surfaces also repel oils, so that fingerprints are less likely form readily on these surfaces.


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Hi Nikki,

The way these work is to put a coating or structure on the glass that prevents water from sticking to it.  One possible way to do this is to make tiny nanocones that are so small and pointy that water can't squeeze between them.  Since water has to balance on their tips, it can't really stick to the surface and rolls off easily.  If you make a window coated with something like this and it rains, the water forms droplets that roll off rather than sticking to it.  Once the rain stops, the window is dry as all the water has rolled off.

If the window gets dirt on it, the dirt particles are also too big to fit between the cones, so as the water beads up and rolls off, it picks up the dirt particles as well.  That way if you make windows of this material, every time it rains, it's like washing the windows.  This is also a big technology for solar cells, which obviously work best when not dirty.  Rather than needing to clean them, you could make them self-cleaning and let the rain clean them for you. jpetruccelli, Wed, 30th Apr 2014

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