Chiral nanotubes of polyaniline synthesized by a template-free method

Abstract

Chiral nanotubes of polyaniline (PANI) were successfully synthesized by a template-free method in the presence of (S)-(−)-2-pyrrolidone-5-carboxylic acid [(S)-PCA)] or (R)-(+)-2-pyrrolidone-5-carboxylic acid [(R)-PCA] as the dopant for the first time. The tubular morphologies of the resulting PANI–(S)-PCA and PANI–(R)-PCA were confirmed by SEM and TEM images. The tubes are 80–220 nm in outer diameter and 50–130 nm in inner diameter. It was proposed that the micelles of aniline–(S)-PCA or (R)-PCA, which were formed due to the hydrophobic aniline and the hydrophilic -COOH group of PCA, played a “template” role during the formation of the chiral nanotubes. These chiral nanotubes showed optically active and electrical properties. In particular, a positive and a negative Cotton effect corresponding to a helical screw of the polymer main chains was observed in the chiral nanotubes. The structural characterization measured by FTIR and X-ray diffraction indicated that the configuration of PCA did not affect the main chains of the chiral nanotubes; however, short-range ordering at 2θ = 6.43 (d = 13.73 Å) was significantly observed from the chiral nanotubes, which might result from the chiral character of the dopant.