ABSTRACT
Abstract Swift heavy ion irradiation effects in Kapton-H polyimide have been investigated using thermally stimulated depolarization current (TSDC) technique. The Kapton-H samples were irradiated with 50 MeV Si, 50 MeV Li, 75 MeV O and 50 MeV Ni using Pelletron facility at the Nuclear Science Centre, New Delhi. The range of fluence varied from 1011 to 1013 ions/cm2. The two major relaxation processes in Kapton-H polyimide viz. β-relaxation associated with dipolar nature of the carbonyl groups and α-relaxation associated with the space charge relaxation process are both affected by ion irradiation. The TSDC spectra obtained for various poling temperatures (80-250◦C) and poling fields (40-600 kV/cm) of irradiated samples reveal, on the one hand, a significant loss in the β-relaxation due to demerization of carbonyl groups and, on the other hand, there is an increase in the space charge relaxation (α-relaxation) owing to the formation of new energy trap centers. Though the general behaviour of the TSDC spectra is not much affected by the nature of ion, the fluence and the energy of the ion play a significant role in modifying these relaxation processes. Some new radiation induced relaxation processes due to increase in water absorption (γ -relaxation) and unsaturated bond formation (δ-relaxation) have been recognized. The distribution of the relaxation times for the TSDC spectra has been estimated using the Cole-Cole distribution function. The Cole-Cole distribution curves show the formation of new sub-polar groups with different characteristic times. The different relaxation parameters viz. activation energy and relaxation time have also been calculated.
