Surface-potential decay due to surface conduction

The time dependence of the surface potential of an insulating material is t heoretically investigated in the case of simultaneous surface and volume oh mic conduction. When the material presents a constant surface conductivity, the first part of the decrease with time of the surface potential is stron gly influenced by the initial distribution of charges and cannot be used to determine the surface conductivity. On the other hand, at rather long time s after the surface has been charged, the potential of the surface follows an exponential variation with time, the expression of the corresponding tim e constant is given in different cases. This model is found in good agreeme nt with experiments performed with photo-oxidized epoxy resins placed in a humid atmosphere.