Electrochemical preparation of chiral polyaniline nanocomposites

Optically active polyaniline colloids have been generated in high yield via the electrohydrodynamic polymerisation of aniline in the presence of 1.0 mol dm(-3) (+)- or (-)-camphorsulfonic acid as dopant using colloidal silica (5% w/w) as dispersant and an applied potential of +0.8 V (vs. Ag/AgCl). Both the rate of polymer formation and the degree of chiral induction in the polyaniline chains were enhanced compared to colloid formation using polystyrenesulfonate (PSS) as steric stabiliser. Higher chiral induction was achieved using 10% w/w silica as dispersant, while lower silica concentrations (e.g., 2.5% w/w) led to over-oxidation. Lower (+)-HCSA concentrations (less than or equal to 0.5 mol dm(-3)) also caused over-oxidation. The dispersions using 5 and 10% w/w silica were very stable, showing unchanged chiroptical properties after 3-4 months. The particle size (300-600 nm) increased with increasing polymerisation time. Transmission electron micrographs (TEM) studies on the dried PAn.(+)-HCSA/silica colloid also showed large (200-600 nm diameter) particles, which on high magnification were seen to be nanocomposites consisting of individual polymer-coated silica particles (ca. 20 nm) fused together to give a raspberry-like morphology. (C) 1999 Elsevier Science S.A. All rights reserved.