Influence of water layers on the electrical behaviour of polymer foils submitted to AC air coronas

Since any solid surface exposed to a gaseous atmosphere is covered with a water layer, interactions between a corona discharge and a polymer surface have to proceed through the water layer which already initially exists on that surface. At the beginning of corona exposure, forces acting on the water layer are predominantly repulsive forces which are exerted by the corona induced aerodynamic flow, and which lead to evaporation processes but, after a certain corona exposure duration, attractive forces, due to the dipoles grafted in increasing number on the surface oxidized by the corona discharge, prevail. The paper focuses on the transition phenomena which bring the first stage to the second one.