EPR study of polyaniline highly doped by p-toluenesulfonic acid

Magnetic, relaxation and electronic dynamic parameters of paramagnetic centers in crystalline domains of polyaniline highly doped by p-toluenesulfonic acid (PANI-PTSA) as well as PANI-PTSA dispersed in poly(methyl methacrylate) (PANI-PTSA/PMMA) were studied by the 3-cm (9.7 GHz) and 2-mm (140 GHz) wavebands EPR. At both wavebands these polymers demonstrate the Lorentzian single line with the Dysonian contribution indicating intrinsic conductivity of metal-like domains ca. 1500-4000 S/cm at room temperature. Effective conductivity of the polymer is defined by Q3D delocalization of charge carriers within such domains and their Mott variable range hopping between the domains dominating its micro- and macroscopic conductivity. It was shown that the interaction of the charge carriers with the lattice phonons governs the intradomain charge transfer at high temperatures. Dimensionality of the system increases with the polymer dispersion in an insulating matrix. Dipole-dipole interaction of polarons with oxygen biradicals reversibly changes the relaxation of the spins in the initial and dispersed polymers. These paramagnetic centers strongly interact below and weakly above critical temperature T_c of the phase transition that leads to an extremal temperature dependence of the polymer linewidth. The dependence of T_c on electron precession frequency and/or on the PANI-PTSA dispersion in an insulating matrix was revealed. Spin relaxation and dynamics were analyzed to be non-correlated with charge transfer in PANI-PTSA that contradicts the “single conducting chain” model and justifies the formation of Q3D metal-like domains.