Non-exponential NMR relaxation in heterogeneously doped conducting polymers

Nuclear relaxation has been theoretically investigated in solids with strong heterogeneous distribution of electronic spins. The competition between direct relaxation by electronic spins and nuclear spin diffusion leads to a relaxation which consists of a weighted sum of exponentials. Numerical solutions of this problem have been derived. Taking advantage of these results, proton relaxation data showing a strong nonexponential behaviour, obtained in partially protonated polyaniline, are shown to be well accounted for in the framework of the conducting islands picture.