Dielectric constant/loss measurements in pristine and 75 MeV oxygen-ion irradiated kapton-H polyimide

The dielectric constant (epsilon') and loss factor (epsilon") measurements have been made in pristine and 75 MeV oxygen-ion irradiated (fluences: 1.8 x 10(11), 1.8 x 10(12) and 1.8 x 10(13) ions/cm(2)) kapton-H polyimide in the temperature region 20-240 degrees C at different frequencies ranging from 1 kHz-4 MHz. There is an overall decrease in epsilon' in irradiated samples. The decrease in epsilon' is more in samples irradiated with high fluences. In pristine kapton-H sample, the initial rapid fall in epsilon' with temperature has been ascribed to the loss in absorbed water (gamma-relaxation). The increase in crystallinity, dipolar relaxation (beta-relaxation) and space charge relaxation (gamma-relaxation) governs the high temperature epsilon'. In irradiated samples, the ion irradiation results in an enhancement of gamma-relaxation, which significantly affects the low-temperature epsilon' behaviour. The decrease in epsilon' with temperature above 40 degrees C has been associated with the demerization of carbonyl groups due to high-energy ion irradiation. In the high-temperature region (above 140 degrees C), the radiation induced free radical cross-linking has been held responsible for decreasing epsilon' with temperature. The loss peaks in epsilon"-T curves appearing around 40-50, 80-120 and 140-180 degrees C represent the gamma, beta and alpha-relaxations, respectively.