Solubility and rheological characterization of polyaniline base in N-methyl-2-pyrrolidinone and N,N′-dimethylpropylene urea

The thermodynamic ‘goodness’ of N-methyl-2-pyrrolidinone (NMP) and N,N′-dimethylpropylene urea (DMPU) as solvents for polyaniline (PANI) (emeraldine base) were compared by studying the dilute solution viscometry of solutions of PANI in NMP and DMPU. The intrinsic viscosity of PANI polymer in NMP was found to be 0.71 dl g−1, whereas the same polymer in DMPU had an intrinsic viscosity of 0.77 dl g−1, which indicates that DMPU is a ‘better’ solvent for PANI. The rheology and rheological stability of solutions of PANI in NMP and DMPU were studied by cone and plate rheometry. A 10% PANI solution in NMP gelled within 60 min, whereas a 17.5% solution in DMPU did not show any change in its viscosity for as long as 400 min. Solutions of PANI (10–17.5%) in DMPU displayed prominent shear thinning behaviour at lower shear rates (below 3 s−1 and Newtonian behaviour at higher shear rates (3–15 s−1). A solution of 10% PANI in NMP showed a similar prominent shear thinning followed by a gradual decrease in viscosity with an increase in shear rates, presumably due to breaking of the ‘weak’ thixotropic gel.