Stability of polytetrafluorethylene electrets in dependence on material structure

Electret properties of nonoriented polytetrafluoroethylene (PTEE) films of different molecular structure were investigated. The structure was modified by using different heat-treatment conditions, the changes in structure being determined by infrared spectroscopy and wide-angle X-ray diffraction methods. The stability of negatively charged electrets was found to decrease with the decrease of crystallinity, longitudinal and transverse crystallite sizes, and the increase of the part of conformation defects. In a far-infrared region, absorption bands were associated with the part and regularity of folded regions in the crystal which are supposedly responsible for the formation of shallow traps for negative charges. The kinetics of the isothermal discharge of positively charged electrets appeared to be less sensitive for the structural modification of films. Positive charge localization either in the paracrystal phase regions or on the surface states is assumed.<
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