=chemistry =explanation
When different materials are
rubbed together,
charge transfer
happens between them. Why that happens is poorly understood, but here is
my working theory:
Friction causes removal of surface material
(abrasion) which implies that localized stresses are sufficient to break
some bonds. That explains the generation of charged species, which don't
normally exist in most materials and are needed to explain charge transfer
happening.
The tert-butyl carbocation is relatively stable because of
multiple resonances to isobutene + H+. This principle is why polypropylene
tends to become negatively charged by friction: friction causes some
molecules to fragment into small carbocations and large polymer chain
fragments with negative charges delocalized on double bonds. Some of those
carbocations then diffuse into the other material.
Other materials
have different amounts of positive and negative small ions produced by
friction, and that is the key difference between materials for charge
transfer by friction between dissimilar materials.
I was recently considering the
nature of the triboelectric effect because:
1) Filter masks have
become more important because of COVID-19, and electrostatic effects are
important for the effectiveness of N95 masks. It may be worthwhile to use a
polypropylene layer (such as a standard surgical mask) in contact with a
cotton layer for filter masks to
improve their
filtration.
2) I now suspect that mineral deposition on the
inside of polymer pipes is partly electrostatic in nature, with small
particles electrostatically adhering to the polymer surface, and mineral
deposition occurring on those particles.