Polyaniline (PANI) nanofibers with small diameters and long lengths are of great value. However, it is difficult to synthesize them in a low-acid environment due to the competing coagulation of long-chain oligomers into irregular structures with low solubility.

Qiuyu Zhang and colleagues, Northwestern Polytechnical University, Xi’an, China, reported an effective method to successfully transform irregular PANI structures into nanofibers with a high aspect ratio. The fibers have a diameter of 46–145 nm, are several micrometers long and have a smooth surface. The team prepared them in 0.010 M HCl solution by adding trace superparamagnetic Fe₃O₄ microspheres to the reaction system and applying a magnetic field.

Morphological evolution shows that aniline first polymerizes on the surface of the Fe₃O₄ microspheres to form a PANI shell. Once the thickness of the coating shell exceeds a critical value, growing nanofibers can be observed. Magnetism aligns the microspheres into chains, which effectively suppresses secondary growth of the PANI nanofibers and optimizes their narrow diameter distribution. This method has the potential to be leveraged beyond PANI, embracing the broad class of conducting polymers to prepare nanofibers.

• Fabricating and Tailoring Polyaniline (PANI) Nanofibers with High Aspect Ratio in Low Acid Environment under Magnetic Field,
  Yong Ma, Yanhui Chen, Ang Mei, Mingtao Qiao, Chunping Hou, Hepeng Zhang, Qiuyu Zhang,
  Chem. Asian J. 2015.
  DOI: 10.1002/asia.201500826