Glass coatings

[Mr Skeptic]

I was wondering what people could tell me about coating glass, particularly windshield glass, to make it better. Normally, glass is somewhat hydrophilic, which is annoying because water droplets can form on it, and stick to it.

 

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Some examples that I know of: A coating of detergent left on glass will prevent fog from building up on the glass, eg on the inside of a windshield or on a bathroom mirror, by breaking the surface tension of water droplets. However, it will come off when washed, though it will stay for quite a while otherwise.

 

A thin coating of titanium dioxide will make glass hydrophilic and also act as a catalyst for decomposition of organic compounds with UV. It is called self-cleaning glass. It also somewhat prevents nonpolars from sticking on it. With UV, apparently it becomes superhydrophilic with a contact angle of nearly 0 degrees. It should also prevent fogging, and make rain drops spread into a sheet. But why is it not used much?

 

Alternately, applying trimethylsilanol (CH₃)₃SiOH to silica should make it hydrophobic enough to prevent water droplets sticking to it. This is particularly seen in "magic sand" where the hydrophobic sand has some interesting and fun properties.

 

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Anyone know if these or other coatings can be applied to improve windshield glass?

[DrDNA]

Yes. It is done all the time. There are a number of silanes and alkoxy silanes on the market to change the properties of glass. Rain-X and Rain Dance are probably the most popular glass (windshield) treatments for consumer use.

[John Cuthber]

"Normally, glass is somewhat hydrophilic, which is annoying because water droplets can form on it, and stick to it."

The problem is that the glass isn't normally hydrophilic enough, not least because it gets dirty. The titania coatings work quite well, I guess they aren't popular because they are expensive or not durable.

 

Silanising glass with things like dichlorodimethylsilane solution makes them very hydrophobic. That might be what the products DrDNA refers to use.