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

Abstract

The dielectric constant (ϵ′) and loss factor (ϵ″) measurements have been made in pristine and 75 MeV oxygen-ion irradiated (fluences: 1.8×1011, 1.8×1012 and 1.8×1013 ions/cm2) kapton-H polyimide in the temperature region 20–240 °C at different frequencies ranging from 1 kHz–4 MHz. There is an overall decrease in ϵ′ in irradiated samples. The decrease in ϵ′ is more in samples irradiated with high fluences. In pristine kapton-H sample, the initial rapid fall in ϵ′ with temperature has been ascribed to the loss in absorbed water (γ-relaxation). The increase in crystallinity, dipolar relaxation (β-relaxation) and space charge relaxation (α-relaxation) governs the high temperature ϵ′. In irradiated samples, the ion irradiation results in an enhancement of γ-relaxation, which significantly affects the low-temperature ϵ′ behaviour. The decrease in ϵ′ with temperature above 40 °C has been associated with the demerization of carbonyl groups due to high-energy ion irradiation. In the high-temperature region (above 140 °C), the radiation induced free radical cross-linking has been held responsible for decreasing ϵ′ with temperature. The loss peaks in ϵ″–T curves appearing around 40–50, 80–120 and 140–180 °C represent the γ, β and α-relaxations, respectively.