Abstract
Hydroxypropylcellulose (HPC) has been used as a steric stabilizer for preparing polyaniline dispersions using the route of oxidative dispersion polymerization of aniline. Using strongly acidic conditions (1โmolโ
l^โ1^โHCl), low temperature of about 2โยฐC and a concentration of aniline as low as 0.5%, ammonium peroxodisulfate at 1.25% and hydroxypropylcellulose concentrations at 0.5โ1โgโdโl^โ1^, unstable dispersions were obtained not only in water but also in aqueous alcohols (ethanol and methanol) up to at least 70โvol% alcohol. In contrast, dispersions that remained stable for at least 72โh were obtained when the alcohol concentration of the medium was as high as about 80โvol%. Kinetic studies of the polymerization systems suggested that success in the latter case was due to a lowering of the rate of polymerization. Transmission electron microscopy studies showed that dispersion particles prepared in 80โvol% alcohol media are spherical in shape and their diameter decreases with increasing stabilizer concentration. However, a change of morphology from spherical to aggregated needleโshaped was observed when the rate was increased by increasing the aniline concentration from 0.5% to 0.75% gโdโl^โ1^ in the above recipe. The aggregated particles were found to be broken down to spherical nanoparticles when the asโprepared dispersions were sonicated for about 30โmin. The sonicated dispersion on drying showed the presence of fractal clusters of polyaniline particles in the dried film. The fractal dimension was determined to be 1.77 which agreed well with the theoretical value determined by computer simulation based on a diffusion limited clusterโcluster aggregation model in three dimensions.
ยฉ 2001 Society of Chemical Industry