Electrons on dielectrics and contact electrification

Surfaces of dielectrics (insulators) often become charged following contact with metals, semiconductors, and dielectrics with or without rubbing. The mechanism and participants in the charge transfer (electrons or ions), although widely investigated, are still controversial. Whereas the identity of the charge carrier cannot be distinguished by electrostatic measurements, we have recently found that charges on a dielectric surface, e.g. for polymers like Teflon (polytetrafluoroethylene or PTFE) and Lucite [poly(methylmethacrylate) or (PMMA)], can carry out different chemical redox reactions, e.g. metal deposition, ion reduction, and chemiluminescence. This suggests that electron transfer occurs in electrification. This chemical approach allows determination of the surface density of electronic charge as well as processes involved in charging and discharging the dielectrics. An overview of this work is presented.