The structure change-induced morphology transition of polyaniline in 1.6-hexanediol aqueous and acid-free solutions: From submicron-spheres to nanofibers

This study shows that the polymerization of aniline monomers in 1.6-hexanediol aqueous and acid-free solutions can produce three-dimensional (3D) polyaniline submicron-spheres and one-dimensional (1D) nanofibers at different reaction stages through a morphology transition process. Fourier transform infrared spectra indicate that the aniline monomers form phenazine-like units in the initial reaction stage, producing polyaniline submicron-spheres with a diameter of ∼400 nm. The hydrogen bonds between 1.6-hexanediol molecules and polyaniline chains serve as the driving force for the polyaniline chains to construct submicron-spheres. However, as the reaction proceeds, the solution acidity increases and the initially formed phenazine-like segments function as the nucleate for the free aniline monomers to polymerize through para-coupling linkage. This process forms polyaniline samples with a structure consisting of a core of phenazine-like units and a shell of para-linked units. In this stage, the newly formed para-linked aniline units exhibit an intrinsic tendency to transit the polyaniline morphology from submicron-spheres into nanofibers. These results indicate that a change in polyaniline structure during the polymerization process can produce different micro/nanostructures at different reaction stages. This finding provides a practical route for the further design and synthesis of different polyaniline micro/nanostructures.