What makes ice 'sticky'?

Submitted by insane_contin t3_11azam8 in askscience

So I'm scraping the ice off of my windshield the other day, and start thinking how does ice stick to the glass and metal of my car? I can understand organic stuff, it probably freezes the water and forms ice with it. But how does it stick to stuff like metal and glass that has no liquid inside of it to freeze too?

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robot_egg t1_j9zq5tz wrote

This is a great question, and waaay more complicated than you might think. There's a symposium on ice adhesion at a scientific conference (the Adhesion Society Annual Meeting) that's been going on for years, which hints at just how complex it must be.

Surface texture can give a mechanical bond via a lock and key effect. But there's also some molecular level interactions; the surface of glass has a lot of Si-O-H groups, which hydrogen bond with water readily. Similarly, most metals have what's called a "native oxide" layer on the surface, which has similar M-O-H groups that can do the same thing.

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NoKnee4545 t1_ja0jb9b wrote

Do you think there is also pressure difference between atmosoheric pressure and ice-glass boundary that plays a part in this?

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robot_egg t1_ja0ks2o wrote

I'm not sure how to think about pressure at that ice-glass interface. Not saying "no", but I'm *guessing* not. I'm an organic chemist; maybe a physical chemist or a physicist could chime in.

Surface *energy* effects at interfaces are very important for adhesion. You can calculate a work of adhesion by summing up the relative surface energies of all the solid/solid and solid/gas interfaces. Both glass and metals tend to have rather high surface energy, making them easy to stick to.

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ma11en69er t1_j9zn5y0 wrote

Similar reason to bubbles forming on the inside of a drinking glass, microscopic textures on the surface of the glass.

For fizzy drinks they provide a place for the gas to escape, for frozen windscreens they form places for the ice to adhere.

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