The preparation of polyaniline waterborne latex nanoparticles and their films with anti-corrosivity and semi-conductivity

An emulsion polymerization of aniline was performed in micellar solution of sodium dodecylbenzene sulfonate (SDBS), dodecylbenzene sulfonic acid (DBSA), or sodium dodecylsulfate (SDS) as both emulsifier and dopant to obtain stable nano-polyaniline (PAN) waterborne latexes. The direct film formability and anti-corrosivity of PAN latexes were studied. The uniform PAN-SDS/polyvinyl alcohol (PVA) composite films were prepared by casting a direct mixture of the PAN latex and PVA aqueous solution. The emulsifier species and concentration, mixing way of emulsifier with aniline, and polymerization solution acidity, have a remarkable influence on the diameter and stability of PAN latex particles. The molar ratio of emulsifier over aniline was optimized for the synthesis of the PAN latex with small particle size and good properties including film formability, anti-corrosivity, and electrical conductivity. The smallest diameters of PAN-SDBS, PAN-DBSA, and PAN-SDS spherical particles determined by laser particle analyzer and electron microscopes are 2500, 40 and 5 nm, respectively. A good direct film formability of the PAN latex nanoparticles was found. The film formed by solution-casting method is thin, smooth and metal-lustrous. The electrochemical impedance spectroscopy was used to evaluate the impedance of the PAN latex films sandwiched between acrylic resin and iron sheet. It is found that the PAN has excellent anti-corrosivity, implying a possibility of direct application as metal anti-corrosive coating. A semi-conductive PAN/PVA nanocomposite film containing a very small amount of PAN nanoparticles exhibits low percolation threshold of PAN concentration of 0.1 wt.%. (C) 2004 Elsevier B.V. All rights reserved.