EPR and charge transfer inH2SO4-doped polyaniline

Abstract

The study of the electron relaxation and dynamics of polaron charge carriers in undoped and ${\mathrm{H}}_{2}{\mathrm{SO}}_{4}$-doped polyaniline (PANI) by means 3-cm (9.7 GHz) and 2-mm (150 GHz) EPR spectroscopy, and ac, superconducting quantum interference device, and dc conductometries is reported. The existence in PANI of polarons with different relaxation and mobility is shown. Spin-lattice and spin-spin relaxation times as well as the intrachain diffusion and interchain hopping rates of these centers were determined separately at 90--330 K by a steady-state saturation method at 2-mm waveband EPR. At the polymer doping an effective spin relaxation decreases due to the formation of metal-like domains of well-coupled chains with three-dimensional (3D) delocalized charge carriers. The mechanism of spin and charge transfer in PANI with different doping levels is analyzed. The macroconductivity and microconductivity of the medium-doped PANI is determined by 3D interdomain and intradomain hopping of charge carriers, respectively. In a heavily doped polymer 1D interdomain and 3D interchain Mott variable range charge hoppings dominate, accompanied with a strong interaction of the charge with the lattice phonons. It is shown that a bipolaron is the preferred charge carrier in doped PANI samples.