Inelastic neutron scattering study of proton dynamics in polyanilines

The inelastic neutron scattering (INS) spectra between 16 and 4000 cm −1 of chemically prepared non-doped (PANI 2A) and 50% protonated (PANI 2S) polyaniline at 20 K are reported. Band frequencies are compared to those estimated from the IR reflectivity. Different types of protons are distinguished in the spectra: (i) For the ‘water-containing’ 2S sample, INS features are consistent with the presence of a crystalline arrangement of the H 2O network within the PANI lattice. (ii) The spectra of the 2S and 2A samples are dominated by bands assigned to vibrations of the benzoic and quinoidal protons. (iii) A continuum of intensity, underneath the bands of the aromatic protons, is tentatively attributed to the recoil of ‘quasi-free’ protons. These protons could be of great relevance to the explanation of the correlation between the protonation degree and the electronic and protonic conductivity.