When different materials are
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.
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