Lateral nonhomogeneous decays of surface charge on Teflon-FEP films

After negatively grid-controlled corona charging of Teflon FEP (fluorinated ethylene propylene) the authors discovered nonhomogeneous charge decays along a lateral surface, i.e., isothermal charge decay of the central region is faster than that of the border region. Similarly, the more rapid decay of the central region can be observed on negative charging of Teflon FEP at elevated temperatures. After negative liquid-contact charging of Teflon FEP this phenomenon of nonhomogeneous decay also exists. The authors feel that these phenomena originate from electron drifts in various regions under different normal components of electret self-field. Surface charge density at any part during the decay process can be estimated by an empirical formula