Certain polymeric solids have the capacity to retain electrical polarization at ambient or lower temperatures for long periods of time (in some cases several years). Electrical polarization can result from the orientation of molecular moities, such as segments in the main chain or side groups, having a permanent dipole moment. Another possible contribution to polarization could arise from the drift of charged impurities during poling and lead to the formation of an asymmetric distribution of space charge. In experiments thermally stimulated discharge (TSD) technique has been employed; it provides quantitative information on the mean activation energies involved in molecular phenomena contributing to polarization. This information is provided through the recording of discharge current which flows between the shorted electrodes as a consequence of depolarization of the electret upon thermal stimulation. Polyacrylonitrile (PAN) film has been selected to investigate the electret effect. TSD of as-cast PAN films reveals current maxima at similar 100 degree C, 140 degree C and 190 degree C, which could possibly be associated with mechanically active and dielectric loss transitions previously observed. Films polarized under a low intensity field (5 multiplied by 10**4 Vcm** minus **1) at elevated temperature are capable of retaining electrical polarization, as indicated by the enhancement of TSD maxima at similar 95 degree C and 190 degree C. An increase in field intensity during poling results in the complete absence of TSD currents at similar 95 degree C. It is suggested that the absence of these currents results from the formation of a highly developed level of intermolecular bonding due to dipole orientation.
|Original language||English (US)|
|Number of pages||7|
|Journal||Am Chem Soc Div Org Coatings Plast Chem Prepr|
|State||Published - Jan 1 1975|
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