Ionic transients in an extended chain aromatic hetero-cyclic polymer

In an effort to better understand the process of charge transport in extended chain aromatic hetero-cyclic polymers we have made detailed studies of d.c. conduction in one such rigid rod polymer, viz. poly(p-phenylene benzobisthiazole) or PPBT *** Two types of transient currents have been measured. One of these is the gradual decay of current over a long period of time in a PPBT sample exposed to a step function voltage. Typically the current I drops by about three orders of magnitude over a period of six hours and, when plotted on a log-log graph, exhibits a series of linear segments I ∝ t−n. Such measurements were made on samples doped with LiCl, NaCl, CaCl2, LaCl3, etc. The other type of transient, measured for the same samples, resulted when the humidity was suddenly increased from dry conditions to some finite value on a specimen in a quasi-steady state of conduction. A large increase of relative current (ΔI/Imin) occurs, followed by a gradual decrease over a long period of time. Efforts to relate these effects to the nature of the conduction mechanisms and diffusion of water are discussed.