Facile high-yield synthesis of polyaniline nanosticks with intrinsic stability and electrical conductivity.

Chemical oxidative polymerization at 15 degrees C was used for the simple and productive synthesis of polyaniline (PAN) nanosticks. The effect of polymerization media on the yield, size, stability, and electrical conductivity of the PAN nanosticks was studied by changing the concentration and nature of the acid medium and oxidant and by introducing organic solvent. Molecular and supramolecular structure, size, and size distribution of the PAN nanosticks were characterized by UV/Vis and IR spectroscopy, X-ray diffraction, laser particle-size analysis, and transmission electron microscopy. Introduction of organic solvent is advantageous for enhancing the yield of PAN nanosticks but disadvantageous for formation of PAN nanosticks with small size and high conductivity. The concentration and nature of the acid medium have a major influence on the polymerization yield and conductivity of the nanosized PAN. The average diameter and length of PAN nanosticks produced with 2 M HNO(3) and 0.5 M H(2)SO(4) as acid media are about 40 and 300 nm, respectively. The PAN nanosticks obtained in an optimal medium (i.e., 2 M HNO(3)) exhibit the highest conductivity of 2.23 S cm(-1) and the highest yield of 80.7 %. A mechanism of formation of nanosticks instead of nanoparticles is proposed. Nanocomposite films of the PAN nanosticks with poly(vinyl alcohol) show a low percolation threshold of 0.2 wt %, at which the film retains almost the same transparency and strength as pure poly(vinyl alcohol) but 262 000 times the conductivity of pure poly(vinyl alcohol) film. The present synthesis of PAN nanosticks requires no external stabilizer and provides a facile and direct route for fabrication of PAN nanosticks with high yield, controllable size, intrinsic self-stability, strong redispersibility, high purity, and optimizable conductivity.