Fractal growth kinetics and electric potential oscillations during electropolymerization of pyrrole.

Fractal growth, growth kinetics, and electrical conductivity of aggregates obtained during electropolymerization in the systems (A) pyrrole-4-toluene sulfonic acid silver salt (4-TSS)-acetonitrile, (B) pyrrole-4-TSS-ZnSO(4)-acetonitrile, and (C) pyrrole-4-TSS-aniline-acetonitrile were investigated. In the case of system (A), effect of [4-TSS], [pyrrole], field intensity, and solvents H(2)O and CH(3)OH on morphology, fractal character, and growth kinetics was also studied. Fractal growth data were examined in detail. During studies on system (A), electric potential oscillations were observed and subjected to detailed study. The results indicate that fractal growth pattern and electric potential oscillations are inter-related. The mechanism of development of fractal growth, dendritic structure, and electric potential oscillations is discussed in terms of diffusion-limited aggregation and modified Diaz's mechanism, which explains the random movement of radical cations.

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.

Growth patterns of dendrimers and electric potential oscillations during electropolymerization of pyrrole using mono- and mixed surfactants.

Fractal and dendrimer growth patterns of polypyrrole were obtained during electrochemical polymerization of pyrrole in systems (A) pyrrole-sodium dodecyl sulfate (NaDS)-water and (B) pyrrole-NaDS-cetyl trimethyl ammonium bromide (CTAB)-water. Different morphological transitions including compact → flower-like and fractal → dendrimer → fractal were observed depending on experimental conditions. Growth kinetics during electropolymerization of pyrrole was studied. Growth rate was found to be higher in system A than in B. Effect of [NaDS], [pyrrole], and field intensity on morphology and weight of polymer aggregates was also studied in both the systems. Different empirical equations were obeyed under different conditions. Electropolymerized aggregates were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), electrical conductivity measurement, and reflectance spectroscopy. TEM studies revealed that the particle size decreased to ∼140-200 nm in the presence of CTAB. The decrease in particle size on addition of CTAB was also observed in XRD studies. Reflectance spectra of the polymer aggregates support the large π-conjugation in the dendrimer. During electropolymerization, oscillations in potential were monitored as a function of time. Results indicated that growth pattern and electric potential oscillations were interrelated. In the case of fractal growth, the amplitude of chaotic oscillation was higher than the amplitude of oscillation during the growth of dendrimer. Growth morphologies and electric potential oscillations have been explained on the basis of modified Diaz's mechanism.