Counter-ions dynamics in a conducting polymer. Polyaniline protonated with camphor sulfonic acid (Pani-CSA). A quasielastic neutron scattering study

Complete text of publication follows. Pani-CSA films were studied that exhibited a metallic character between 300 and 250 K. Below 250 K, they turned insulating via a broad transition. The explanation of such a behavior is still at the origin of a lot of controversies. We carried out IQNS measurements at ILL using IN6 and IN16 spectrometers on partially deuterated and fully protonated films. The obtained results suggest that the polymer chains can be considered as stiff objects whose dynamics is only vibrational in nature. The origin of the quasielastic broadening recorded on IN6 could be assigned to the motion of methyl groups of the CSA ions which have been found dynamically non-equivalent. Their dynamics is described in terms of a 'logGaussian' type distribution of correlation times whose position and width in energy are temperature dependent. For the highest temperatures (240-350 K), and additional contribution has been revealed in the energy range of IN16 which might correspond to a motion of the whole CSA molecule. It should be noted that this dynamical transition is precisely occurring in the same temperature range than the metal-insulator transition. (author)