Effect of humidity on contact electrification due to collision between spherical particles

This paper reports an experimental study of the contact electrification (CE) that happens when glass spheres of identical materials collide under different ambient relative humidity (RH) conditions. The experimental results indicate that the net charge on a sphere from a single collision is significantly altered by varying the RH level; the charge increases with increasing RH at low humidity, and then decreases at high RH conditions. The net charge reaches a maximum in the 20%–40% RH range. To explain the dependence of the CE on RH, we propose a model which yields predictions in agreement with the experimental data. The model also reveals how CE can be affected by temperature and surface absorption energy.