Nanostructured growth patterns and chaotic oscillations in potential during electropolymerization of aniline in the presence of surfactants.

Polyaniline nanoparticles were synthesized by simple electrochemical polymerization of aniline in systems (a) aniline-sodium dodecyl sulfate (NaDS)-dodecylbenzene sulfonic acid (DBSA)-H(2)O and (b) aniline-NaDS-DBSA-cetyltrimethyl ammonium bromide (CTAB)-H(2)O. Different morphologies including compact and fractal/dendrimer were observed at different experimental conditions. Fractal dimension was calculated by the box counting method. Growth kinetics during electropolymerization of aniline in both of the systems was studied by measuring the weight of polymer aggregates as a function of time. Growth rate was found to be reduced in system (b) due to coordination of CTAB with the growing polyaniline chain. The weight of polymer aggregates was found to depend on field intensity and attains a maximum value at a critical field intensity 4.0 V/cm. Beyond this critical field intensity, the growth rate was decreased due to loss of conjugation and degradation of the polymer backbone. Electropolymerized aggregates were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and electrical conductivity measurements. Nanosized polyaniline was formed, with particle diameters in the range of 10-200 nm, as evident by TEM studies and supported by XRD studies. FT-IR spectroscopy established the formation of hyperbranched polyaniline chains. During electropolymerization, oscillations in potential were monitored as a function of time at different experimental conditions. A suitable mechanism for fractal growth of polyaniline was also proposed.