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 H2O 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.