Self-assembled films of poly(o-ethoxyaniline) complexed with sulfonated lignin

The interaction of poly(o-ethoxyaniline) (POEA) doped with HCl and sulfonated lignin (SL) was investigated using UV-Vis spectroscopy in order to probe the influence of pH and quantity of SL on the formation of a polyelectrolyte complex. The introduction of SL into the HCl doped POEA solution screens the positive charges of the protonated POEA allowing further protons to be pumped into the conducting polymers thus increasing its doping level. In addition, the strong interaction between these two electrolytes caused POEA to remain doped within a wide pH range. Layers were built from aqueous solutions of the complex formed by POEA and SL which were alternated with either pure POEA or sulfonated polystyrene in the form of layer-by-layer films. The resulting multilayer films remained doped even at pH 9.0, due to the strong complex formation, which prevents POEA from deprotonating. Surface potential measurements showed that the potential for the POEA + SL complex is more positive than for films with each layer investigated separately, thus confirming the strong interaction between POEA and SL. (C) 2002 Elsevier Science B.V. All rights reserved.