Moisture effects on the electrical conductivity of Kapton polyimide

The electrical conductivity of Kapton polyimides (PI) at elevated temperatures and in the dry state has been widely reported in the literature. Measurements at ambient temperature and in presence of moisture are less well documented. This paper reports an experimental investigation of the effect of water (at 100% relative humidity) and ionic contaminants (NaCl) on the electrical conductivity in 7.5 and 125 μm thick PI. Measurements were carried out at 30°C with electric fields in the range 2.7 × 10 2-1.6 × 10 3 Vcm -1. Results obtained are as follows: (i) the electrical conductivity of wet polyimide is several orders of magnitude larger than that of dry samples; (ii) variations of one order of magnitude in the electrical conductivity were observed among otherwise similar samples; (iii) the current decay follows a power law for time of the order of 10 3s before a pseudo steady-state value is observed (I 0), then a subsequent increase of the current is followed by a final stable steady state; (iv) a plot of I 0 vs. the applied voltage for fields in the range reported above appears to be linear; and (v) NaCl concentration in the range 10 -3-0.5M has only a moderate effect on the measured conduction.