Estimation of charge mobility and charge density in polyimide film by charge chromatography

To investigate the electrical conduction properties in polyimide affected by moisture absorption, charge mobility was measured by "charge chromatography". A time-dependent charge distribution was monitored by an electroacoustc method when a pulse voltage was superposed on a dc bias voltage. In this newly proposed technique, the generation and traveling of charges were visualized. Charge density and charge mobility were individually determined from the measurement results of both charge chromatography and conductivity measurement. The conductivity of a moisturized specimen was 125-hold higher than that of a dry sample. Although both charge mobility and charge density increased by moisturizing the sample, it was concluded that an increase in charge density plays a dominant role in an increase in conductivity. It is considered that the dissociation of impurities in polyimide by moisture absorption leads to the increase in mobile charges.