Re: What properties make some materials gain e- by contact (

Hi Joseph!

What you're talking about is the physics behind the "triboelectric series", which is the list of materials placed in order of polarity of their "contact electrification."

As far as I know, the reasons for the ordering of the triboelectric series of insulating materials are still a mystery. For bulk metals the ordering is understood: it is caused by the Work Function differences between metals. (For example, look into the therory behind thermocouples and semiconductor junctions.) For single atoms it is also understood: it is covered under Chemistry, and is part of the theory of chemical bonds (what atom gets more electrons during ionic or asymmetrical bonding.) But for bulk insulating materials, and even for large molecules, I believe the details are still a mystery.

Many things affect the polarity: only the atoms on the surface should play a part, therefore the slightest contamination or adsorbed water or oxide film can affect the results. Even mechanical events have an effect. For example, when polished plastic is rubbed on matte-finish plastic, there is a separation of charges even if both surfaces are made from the exact same plastic! What the heck causes that???