Space charge distribution and crystalline structure in quenched polytetrafluoroethylene

Three polytetrafluoroethylene (PTFE) specimens were prepared under different cooling rates after sintering. The space charge distribution in PTFE specimens under direct current electrical field was measured by the pulsed electro-acoustic method (PEA). It was found that the amount of space charges decreased and field distribution tended to be uniform in the quenched specimen. Differential scanning calorimeter (DSC) and wide-angle X-ray diffraction (WAXD) showed that crystallinity and crystalline size of PTFE decreased after quenching whereas the crystalline form of PTFE remained the same. The structure of crystallites became disorderly and imperfect. All the changes in crystalline structure after quenching might decrease the number of space charges trapped in specimens and enhance the transmission of the charge-carriers in amorphous regions, which probably resulted in a decrease of the accumulation of space charges.