Synthesis and characterization of polyaniline nanoparticles in phosphonic acid amphiphile aqueous micellar solutions for waterborne corrosion protection coatings

Abstract

Polyaniline (PANI) dispersions consisting of 270 to 380 nm sized particles were prepared by oxidation with ammonium peroxydisulfate (APS) in n-decylphosphonic acid (DPA) micellar solutions. The green dispersions do not undergo macroscopic precipitation for more than a year. The synthesized DPA doped PANI exhibited enhanced electrical conductivity (3.6 S cm-1) compared with DPA-PANI (2.3 x 10-4 S cm-1) prepared by postsynthesis treatment of the PANI-base with DPA. It was shown that through protonation with decylphosphonic acid, polyaniline showed a significantly enhanced solubility in common organic solvents like chloroform, xylene, etc. The synthesized PANI was characterized by intrinsic viscosity, solubility, FT-IR, conductivity, SEM, and TGA measurements. The wide-angle X-ray diffraction study revealed the appearance of a peak located at low angles (d = 29.4-35.3 Å) suggesting the formation of layered structure of PANI backbone separated by long alkyl side chains of DPA. The anticorrosive performance of the bilayer coatings composed of a bottom layer of DPA doped polyaniline covered with a polyvinyl butyral topcoat, have been demonstrated for steel exposed to neutral saline solutions. It was found that the inhibitive properties of DPA dopant provides further protection to the base metal through smart release when damage is produced on the surface of the coating.