Impact tribocharging of soft elastic spheres

The transfer of charge between a solid sphere and a metal plate during an oblique collision has been studied, using larger, more compliant elastic spheres than in previous studies. This relatively slow collision with large maximum strain allowed the normal and tangential impact forces to be measured directly, and the cumulative rolling and sliding contact areas to be deduced using a dynamic model. A rich variety of charging behaviour was observed for different collision regimes, and suggests very different charge transfer mechanisms for sliding, non-sliding, heavy and light contact. The charge transfer to initially-negative and initially-positive spheres was also strikingly different. Although the reasons for this could not be definitively determined, several hypotheses are discussed in detail, including mechano-ion transfer, bulk material transfer, and the effect of the spatial distribution of the initial charge on the statistical distribution of charge transfer events.