Raman spectroelectrochemical study of polyaniline and sulfonated polyaniline in solutions of different pH

Raman spectroelectrochemical study has been done with electrochemically prepared films of polyaniline and a copolymer of polyaniline and metanilic acid using a green laser excitation (532 nm). The experimental variables included solutions of different pH between 0.5 and 9.0, and varying electrode potential between 0.0 and 0.8 V versus Ag/AgCl. Raman bands within the wavenumber limits of 500–1700 cm−1 have been analysed, and their changes, proceeding with varying of electrode potential and solution pH, have been interpreted. It has been stressed that the spectral changes of polymer films proceed continuously rather than stepwise by changing the electrode potential. Considering leucoemeraldine and pernigraniline forms of polyaniline as fully reduced and oxidised structures, respectively, it could be concluded that many different redox forms can exist between these two limiting forms, rather than the only possible emeraldine form.