Investigation of corona charge stability mechanisms in polytetrafluoroethylene (PTFE) teflon films after plasma treatment

In this paper, the corona charge stability in electret polytetrafluoroethylene Teflon film is investigated after the film is treated by radio-frequency plasma. It is found that the charge stability depends strongly on the plasma composition and the film exposure to plasma, especially for negative charge. When a non-metalized film is held horizontally on the ground holder, i.e. with one side facing the plasma, oxygen plasma treatment achieves a superior negative charge retention on the front side, while its rear side retention decreases significantly. Under the same conditions in oxygen/helium and helium plasmas, the charge stability also increases but the potentials are lower compared with pure oxygen plasma after annealing. In a hydrogen plasma, the stability only slightly enhances. If the film is held vertically on the holder, so that both sides contact the plasma, the surface potential on both sides decreases dramatically and arrives at a few volts within 2 min, after annealing at 170°C. By Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), we conclude that oxidation formed on the front side is responsible for increasing the stability of negative charge. The positive carriers, generated in the film during plasma treatment, recombine with charge from corona charging and causes the surface potential in the rear side of the horizontal non-metalized film, or in both sides of the vertical non-metalized film, to discharge after heating.