Contact electrification of polymers

Measurements of the charge produced by rolling or sliding contact between a metal or polymer sphere and a dielectric sheet have been carried out under controlled conditions. The dependence of charge on air pressure was studied. Charge decay and mobilities were estimated. The metal work-function had no effect on charge transfer. The polymer materials was of great importance, polar polymers charging positively with respect to both metals and non-polar polymers. The relation between charge per unit length and the square root of the normal contact force was found, and the time constant for charge transfer was evaluated.