The controlled synthesis of polyaniline microtubes with square inner cross-section and polyazane square microbars

Controlled micro/nanostructures of polyaniline (PANI) were obtained through a chemical oxidative polymerization by changing the concentration of aniline monomer in the presence of citric acid as dopant. It was found that conducting PANI microtubes with square inner cross-section (580-300 nm in diameter and 80 nm in wall thickness) were obtained at a relatively high aniline concentration. When the solution was sufficiently dilute, the polyazane microbars with square cross-section (690-290 nm in side length and 1-40 μm in length) can be made by self-assembly. Structural characterizations of the microbars with square cross-section showed that aniline polymerized product by this method was a new material containing N - N single bonds rather than PANI, which was defined as polyazane by A. G. MacDiarmid. The aniline/citric acid salts are proposed as the templates in the formation of the microtubes with square inner cross-section and microbars with square cross-section based on XRD and SEM measurements. Interestingly, it was found that morphology and molecular structure of the microbars were strongly affected by the reaction time and the concentration of aniline. The molecular structure of the microbars with square cross-section was changed from polyazane to PANI, for instance, when the reaction time increased from 5 h to 168 h. Moreover, the microbars with square cross-section were varied from solid to hollow with square cross-section and which was accompanied by a molecular structural change from polyazane to conductive PANI when the concentration of aniline increased by one order of magnitude (from 1.75 × 10^-2 to 1.75 × 10^-1 mol/L).