Investigation of interaction among polyaniline, organic acid, and water

In this work, gel permeation chromatography (GPC) and UV–vis spectroscopy are used to investigate interaction between organic acid and polyaniline (PANI) in emeraldine base (EB) form at a molecular level. Dichloroacetic acid (DCAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) are chosen to study the changes in the GPC chromatograms and the UV–vis spectra of the diluted EB/N-methyl-2-pyrrolidinone (NMP) solutions when the acid was added in the solutions. The studies reveal that the organic acids form H-bonds with EB in an anhydrous solution. DCAA tends to form H-bonds with EB through intra-chain interactions whereas AMPSA tends to form H-bonds with EB through inter-chains. The inter-chain interaction among EB and AMPSA molecules results in the formation of clusters, which occupy a larger hydrodynamic volume and give much higher molecular weights than un-clustered EB molecules. Due to a strong affinity of AMPSA, water molecules are localized inside the clusters when water is present in the solution. Therefore, a small amount of water can rapidly initiate EB protonation (H2O/AMPSA molar ratio > 5.0) at ambient conditions.