I remember briefly studying the triboelectric effect in Physics but as I now approach the domain of Chemistry, I'd like to know what processes are involved (at the molecular level) when the the triboelectric effect comes into play. What variables (if any) would have have to be considered when conducting an analysis of the triboelectric effect?

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    $\begingroup$ If you already know the "physics" behind the triboelectric effect, then ipso facto, you know the "chemistry" involved as well (it's the same). Physics and Chemistry are human descriptions of the essentially the same thing: our universe. Chemistry looks at the finer details of things...Physics is just the "big-picture" :P $\endgroup$ – paracetamol Jun 24 '17 at 10:51
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    $\begingroup$ ahah you're probably right, I studied it in physics but my lecturer just told us that some "materials" if rubbed with others tend to gain or lose electrons, I just wanted to dig a little bit deeper. I made some reaserches but I've found no detailed explanation even wikipedia says " The triboelectric effect is not very predictable, and only broad generalizations can be made" $\endgroup$ – Gabriele Scarlatti Jun 24 '17 at 11:19

You would've probably heard of the commonly given example, rubbing a glass rod with silk. The glass rod becomes positively charged, and the silk becomes negatively charged.

But why? That's your question I believe, and for that we need to zoom in a little further, until we can see the molecular structure.

Glass, is a polymer mainly composed of silicates. It is a network polymer, with a bunch of $\ce{Si-O}$ groups, as evident in it's structure:

(source: mechanicalengineeringblog.com)

You can observe that some of the oxygens are negatively charged, and are countered by sodium ions.

Now, lets observe silk,

Silk, like most natural fibers, are composed of proteins. These proteins exist as $\alpha$-helices. Sericin is the outermost protein in the silk structure, so I'll show a bit of it's structure,

Now, let's get to the rubbing part!

What happens when you rub them?

You're agitating the two molecules and bringing them in contact. Loose bonds can be broken off. Consider the $\ce{N-H}$ bond in the Sericin structure. It can be easily removed as a $\ce{H+}$ ion, since the resulting negative charge can be shared with the nearby oxygen in the adjacent carbonyl group. This leaves silk with a net negative charge.

This $\ce{H+}$ can now bind to the negatively charged oxygen atoms on glass, giving the glass rod, a postive charge.

I shall end my answer with a note:

Whenever in doubt, look deeper into the structure.


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