Influence of charging conditions of porous polytetrafluoroethylene (PTFE) film electrets on the permeability of membranes

In this paper, the influence of charging conditions on the permeability of porous PTFE membranes is studied by constant voltage corona charging at room and elevated temperatures and by measuring the relative flow rate in water when porous PTFE electret films are used as filter membranes. We found that charging field and charging temperature strongly affect the relative flow rate of water. The structure of porous PTFE, investigated by a scanning electron microscope, is important for understanding the influence of charging conditions on material permeability. The increase of the ratio of bulk charge density to surface charge density of the porous films was performed by thermal treatment during charging. Such porous films may be employed as electret filter membranes for purification of dielectric liquids