Vinod P. Menon

A Mechanistic Investigation of Polyaniline Corrosion Protection Using the Scanning Reference Electrode Technique

Growing environmental concerns regarding the use of heavy metals in coating formulations have lead to a new coating strategy employing inherently conducting polymers (ICPs), such as polyaniline (PANI), as a key component. The principal potential advantage offered by the ICP coating technology is toleration of pinholes and minor scratches. This paper describes the application of the scanning reference electrode technique (SRET) to the study of PANI coatings on carbon steel. SRET results demonstrate that conductive PANI passivates pinhole defects in coatings on carbon steel. In addition, it is shown that phosphonic acid salts of PANI are more effective for corrosion protection than sulfonic acid salts. A model is proposed which entails passivation of the metal surface through anodization of the metal by PANI and formation of an insoluble iron-dopant salt at the metal surface.

Synthesis and Characterization of Organically Soluble Polyaniline and Polyaniline Block Copolymers

Abstract An emulsion process has been developed for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. The process entails forming an emulsion composed of water, a water soluble organic solvent (e.g., 2-butoxyethanol), a water insoluble organic acid (e.g., dinonylnaphthalene sulfonic acid) and aniline. The resulting product is truly soluble in organic solvents such as xylene and toluene, of high molecular weight (Mw >22,000) and film forming. The emulsion polymerization process was also employed to synthesize ABA triblock polymers of polyaniline where the B block is a diamine terminated polymer and the A block is polyaniline. As cast, PANI films were only moderately conductive (10 −5 S/cm). However, PANI conductivity could be enhanced by up to five orders of magnitude by treatment of the films with surfactants or low molecular weight alcohols and ketones. Blends of PANI and plasticizers such as toluenesulfonamide were found to exhibit conductivities up to 100 S/cm. X-ray diffraction studies of cast PANI films help to explain the conductivity enhancement by showing that surfactant and solvent treatments significantly increase the crystallinity and long range ordering of the polymer.