Role of electron-donative dopant molecules in the triboelectrification of polystyrene films

The triboelectrification between iron carrier beads and polystyrene films m olecularly-doped with 50 electron-donative organics are investigated in a n itrogen atmosphere and low humidity (<10% RH) conditions. The electrochemic al oxidation potential of the dopants correlates well with the tribochargin g amount within the framework of a homologous series of dopant molecules, b ut turns out not to be a widely applicable and reliable indication. Conside rations of liquid-phase electrochemical oxidations and solid-phase friction al electrification lead us to use calculated oxidation potentials instead o f the measured one, and it is revealed that a relatively good relation hold s between the calculated potential and the charging amount. However, there still exists some dispersion of the data in the relationship. X-ray photoel ectron spectroscopic measurements of the film surfaces, combined with the a bove findings, reveal that the dopants form charge transfer complexes with environmental dioxygen and that they serve as the positive-charging sites. This is evidenced by an even more reliable relationship between the chargin g amount and the binding energy of O1s electrons. A possible mechanism is p roposed for the positive charging of organic compounds on the basis of the charge transfer model.