Correlation of contact deformation with contact electrification of identical materials

We report an experimental study on the contact electrification produced by two chemically identical glass plates under different contact forces. For the given plate sizes, the mean value of the surface charge density is independent of the contact force, but the standard deviation of the surface charge density increases with increasing contact force, which indicates that the magnitude of charge transfer is enhanced with increasing contact force. The contact between plates of different sizes leads to the systematic transfer of charge in one direction. To understand this effect, finite element modelling was carried out, which shows that the contact between plates of different sizes leads to different in-plane strains developing in the two plates. The surface charge density from contact electrification correlates with the difference in the in-plane strain between the contacted plates. The results suggest that the in-plane strain difference between contact surfaces plays an essential role in contact electrification and may be a key driving force for the charge transfer between chemically identical surfaces.