In situ Raman study of sulfonate-doped polyaniline

The electrochemical behaviour of polyaniline (PANI) is particularly complic ated, with respect to the other conductive polymers, in respect of the two reactions (protonation-deprotonation and oxidation-reduction) which occur s imultaneously, but with different rates; the respective rates of the two re actions vary with the pH of the electrolyte. A further complication arises from the existence of three insulating forms with different oxidation level s. Raman, as well as optical spectroscopies are excellent tools to obtain a n in situ identification of the polymer under polarization. However, it was observed that the connections between Raman/optical features and voltammog rams are far from being straight. A more thorough analysis can be obtained using 'resonant' Raman with several excitating laser lines, because each of these fines is able to enhance;the response of a selected polymer segment. The blue line was expected to lead to the localized polaron excitation, th e red line to the exciton excitation and the near-IR line to the intrachain excitation. The use of red and IR lines brought a splitting of the C=N and C-N+ stretching modes, displaying the large variety of different segments existing at every potential. The broadening of the voltammograms obtained i n weakly acidic media was easily understood; in very acidic solutions, on t he contrary, owing to the sharpness of voltammograms, the complexity of the reactions arising in PANI during its polarization was not at all suspected . In the present work, PANI doped by functionalized sulfonic acids is studi ed. (C) 1999 Elsevier Science Ltd. All rights reserved.