Effect of water absorption on pristine and ion-irradiated kapton-H polyimide using thermally stimulated depolarization current technique

In this paper we report the effect of water absorption on pristine and 75 MeV oxygen ion-irradiated kapton-H polyimide by using the thermally stimulated depolarization current (TSDC) technique. The TSDC spectra reveal two significant peaks at low and intermediate temperatures around 30°C and 110°C termed as γ-peak (absorbed water-relaxation) and β-peak (dipolar-relaxation), respectively. The strength of the low-temperature peak (γ-peak) is affected in the opposite mode for pristine and ion-irradiated samples. A current reversal has been observed at 60°C almost in all the cases; this can be associated with the presence of homocharges. The current reversal that appears here can be correlated with the internally developed field in the sample as the applied electric field is not very high. Activation energy has been calculated by using the Debye relaxation process. The value of activation energy for the γ-peak varies from 0.4 to 0.8 eV. Cole-Cole distribution, a relaxation process, is associated with distribution of relaxation time which can be measured using a distribution function. The enhancement in the distribution of τ can be associated with the dipolar relaxation process owing to the formation of some new radiation-induced sub-polar groups.