Study of vibrational spectra of polyaniline doped with sulfuric acid and phosphoric acid |
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Authors: | Manju Arora Vandna Luthra Ramadhar Singh S K Gupta |
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Institution: | (1) National Physical Laboratory, Dr. K. S. Krishnan Road, 110012 New Delhi, India;(2) Physics Department, Gargi College, Delhi University, Sirifort Road, 1110049 New Delhi, India |
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Abstract: | Vibrational spectra of insulator emeraldine base (EB) form of polyaniline and electrical conductive sulfuric acid-and phosphoric
acid-doped emeraldine salts (ES) were studied in the region of 4000-400 cm−1 at ambient temperature by Fourier transform infrared spectroscopy. Infrared transmittance spectra of EB and ES were investigated
to understand the bonding behavior of different organic and inorganic groups present in the polymeric chains and their structural
variations on protonation by sulfate or phosphate ion inclusion in the polymer salt network. These studies revealed the para-coupling
of deformed disubstituted benzenoid (B) and quinoid (Q) rings with ends capped predominantly by (B4Q1) units. The deformation
of B and Q rings was confirmed by the appearance of many weak bands, very weak bands, and satellite structures in strong transmittance
peaks of polymeric chain-constituting groups. Protonation takes place at the nitrogen sites of Q rings and forms semiquinone
radical ions in ES. The vibrational bands pertaining to B rings, Q rings, B4Q1 units, semiquinone segment, sulfate ions, and
phosphate ions were observed and assigned from these measurements. The shift in peak position of some bands with gain or loss
in intensity and appearance of some new bands were observed in sulfuric acid-and phosphoric acid-doped ES spectra. These variations
are attributed to the formation of new structural groups in ES on protonation and a change in crystalline field by sulfate
and phosphate ion doping for crosslinking the polymeric chains. |
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Keywords: | Vibrational spectra polyaniline sulfuric acid phosphoric acid |
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