Abstract
Water concentration in polyaniline (PANI)/acid solutions containing 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPSA) significantly changes the solubility of PANI and the stability of its solutions. By varying trace amounts of water, we investigated the impact of hydrogen bonds (H-bonds) on PANI chain conformation in solutions of AMPSA/dichloroacetic acid (DCAA) or AMPSA/orthophosphoric acid. UV–vis–NIR spectral changes of these PANI solutions reveal that a competition between H-bond formation and protonation among PANI, AMPSA and water is an on-going process. The H-bonds between the PANI and AMPSA molecules can cause a large red shift in the π b → π q electron transition (the quinoid peak) from ∼630 nm into the near IR (NIR) region. Absent protonation peak (410–490 nm) and blue color of the solution suggest that the H-bond interaction, instead of protonation, is sufficient to cause PANI chains to adopt an “expanded coil” chain conformation in the PANI.AMPSA n /DCAA or H 3PO 4 solutions. Protonation leads to the gelation of PANI solutions. The kinetic mechanism of protonation of the PANI.AMPSA n /DCAA solutions is studied. The activation energy of protonation in the PANI.AMPSA 0.6/DCAA solutions is ∼60 kJ/mol.
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