Charge detrapping in PVDF observed by field induced gas emission

In former experiments we observed a strong gas emission during the poling process of PVDF-films through a porous electrode. This gas emission is induced by the applied electrical field and is measured using a quadrupole mass spectrometer. It can be attributed to the generation of ionic charge carriers at the electrodes and consists predominantly of hydrogen fluoride. When the poling field is switched off, the gas emission increases very fast to a value even higher than under the field. The delay between the switching off of the field and the time when the maximum of this “zero field emission” is reached depends on the poling polarity and the thickness of the sample and increases with the distance between the polarization zone and the porous electrode. We explain this zero field emission by ion detrapping at the polarization zone. After neutralization the ions diffuse out of the sample and give rise to the zero field gas emission. The diffusion coefficient of HF in PVDF can be estimated with these measurements. The results of the experiments are in good agreement with the charge trapping model for the stabilization of the polarization in PVDF