EPR and charge-transport studies of polyaniline

The study of dc and microwave (140 GHz) electrical conductivities using multifrequency electron-spin resonance in undoped and HCl-hoped polyaniline is reported. The accidental quasi-three-dimensional (3D) charge hopping between the pinned and mobile small polarons dominates the bulk conductivity of the emeraldine base form of polyaniline. The increase in mobility and the number of excitations upon light doping of the polymer leads to the isoenergetic interpolaron charge hopping between the polaron and bipolaron states. 1D variable-range hopping of a charge between conducting islands, which correlates with a superslow torsional dynamics of the polymer chains, dominates bulk conductivity bf heavily doped polyaniline at low temperatures. Intrinsic microconductivity is determined by the interaction of the charge with the lattice phonons at high temperatures. Following Epstein and MacDiarmid we propose that emeraldine salt of polyaniline represents a 1D disordered conducting compound consisting of metal-like islands of well coupled chains with 3D delocalized charge carriers.