Thermally stimulated discharge current and fractional polarization studies in polyimide (Kapton-H) samples

In order to understand the relaxation processes responsible for thermally charged polyimide (PI) samples, the thermally stimulated discharge currents (TSDC) and fractional polarization thermally stimulated discharge current (FPTSDC) have been recorded. FPTSDC study is found to be having dipolar as well as space charge relaxation. The appearance of the second peak (i.e. b peak) at different poling field indicated that this peak is attributed to dipolar relaxation in polyimide. The peak position and activation energy do not change with the poling field (Vp), but it is very sensitive to the poling temperature (Tp). The magnitude of peak current has been found to vary with poling field and temperature. The poling field seems to change the reorientation of dipoles associated with b peak. The ? (first peak) and b (second peak) peaks were attributed to the motion of the side chain and the dipole-orientation associated with the residual reactive groups, respectively. The ? peak (third peak) may be due to the space charge polarization or due to charge injected from the electrode. The activation energy and charge released have been found to vary with the poling field, poling temperature and poling time for this peak. FPTSDC spectra are showing two peaks which correspond to dipolar and space charge relaxation, respectively and are in good agreement with TSDC.