EFFECTS OF HUMIDITY ON THE DARK CONDUCTIVITY AND DIELECTRIC-PROPERTIES OF POLY(BENZIMIDAZOBENZOPHENANTHROLINE) THIN-FILMS

The dark conductivity and the dielectric constant of thin films of the conjugated ladder polymer poly(benzimidazobenzophenanthroline) (BBL) are found to exhibit large sensitivity to the relative humidity (RH). Although the dc part of the conductivity shows the largest sensitivity , increasing from 4 x 10(-14) to 5 x 10(-11) S/cm when the relative hu midity changes from 0 % to 50 %, the ac part varies much less under si milar changes in RH. At RH approaching 0 %, the dielectric constant wa s found to be frequency independent and close to 3 over the whole meas ured frequency range (10-10(6) Hz), whereas at 50 % RH the dielectric constant was about 5 at the highest frequency. Thermogravimetric analy sis has also confirmed these findings by detecting about 2 % weight lo ss due to moisture removal from the films. The possible origins for th ese humidity effects on dark conductivity and dielectric properties ar e examined.