Microstructure and charge transport in electrically conducting polypyrrole/poly(p-phenylene terephthalamide) composite fibers

Electrically conducting composite polypyrrole/poly(p-phenylene terephthalamide) (PPTA or Kevlar^R) fibers have been prepared by chemical polymerization of pyrrole within the void structure of never-dried PPTA fibers. The composite morphology has been examined by scanning electron microscopy (SEM) and wide angle x-ray diffraction techniques, which indicate the existence within the fiber interior of a dispersed polypyrrole phase having no preferred direction of orientation. The d.c. conductivity exhibits a temperature dependence characteristic of three-dimensional variable-range hopping in the limit of low temperature; however it begins to diverge from this law at higher temperatures for the more conductive samples. The temperature dependence of the composite fiber thermopower can be understood in terms of the model proposed by Kaiser.