Static electricity

[gonelli]

I know that when you rub a balloon against your hair or a piece of wool that electrons are stripped from them and go across to the balloon, giving the balloon a negative charge. And you can rub a glass rod with a piece of silk and the rod loses electrons, making it positive.

 

But what I don't understand is why the electrons move across to the different materials. What property of the material determines whether it will lose or gain electrons?

 

Any help would be great.

[swansont]

http://en.wikipedia.org/wiki/Triboelectric_effect

[gonelli]

Thank you very much for that link