Space charge in polyimide film after water absorption

A polyimide film exhibits high water absorption because of its imide bonds, which presents problems in practical applications. The PEA method was used to examine the effect of moisture content on space charge formation by measuring the space charge density in polyimide films that had been immersed in distilled water and changes in the space charge distribution over time. A negative d.c. bias voltage was applied from an upper electrode to non-immersed specimens, specimens immersed for 24 hours, and specimens immersed for 48 hours. All three types of specimens showed similar charge densities and waveforms while the bias voltage was being applied, but the immersed specimens showed a higher space charge density after the voltage was removed. Charge tended to infuse into the specimens with immersion, so that space charge remained after the voltage was removed. The space charge was roughly the same in specimens with different immersion times (24 hr. And 48 hr.). The charge density was roughly the same in the non-immersed and immersed specimens while the bias voltage was being applied. Measurement of relative permittivity at room temperature of a polyimide film that had been immersed in distilled water showed that relative permittivity increased with immersion.