An electrochemical procedure, based on the dissolution of a metallic anode in an aprotic solvent, has been used to obtain silver nanoparticles ranging from 2 to 7 nm. By changing the current density, it is possible to obtain different silver particle sizes. The influence of the different electrochemical parameters on the final size was studied by using different kinds of counter electrodes. The effect of oxygen presence in the reaction medium as well as the type of particle stabilizer employed have also been investigated. In some conditions an oscillatory behavior is observed. Characterization of particles was carried out by TEM and UV-vis spectroscopy. The maximum and the bandwidth of the plasmon band are both strongly dependent on the size and interactions with the surrounding medium. The presence of different silver clusters was detected by UVvis spectroscopy. By using this technique, the existence of an autocatalytic step in the synthesis mechanism is proposed.

No abstract

No abstract

Monte Carlo simulations were performed to study the formation of nanoparticles in microemulsions. The influence of the following parameters on particle size distribution (PSD) was investigated:  number of reagent molecules per droplet, surfactant film flexibility, droplet size, presence or absence of autocatalysis by the product, and the fraction of bulk volume made up by droplets. It was found that autocatalyzed reactions with high reagent concentrations and low surfactant film flexibility afforded bimodal PSDs. Particle size increased with reagent concentration when this was low, but at higher reagent concentrations it depended chiefly on droplet size. The dependence of PSD on reaction time confirmed the successive occurrence of well-defined nucleation and growth processes. We have compared the simulation results with experimental data taken from different authors and carried out in our laboratory. Good agreement between both kind of results supports the conclusions of this paper.

In this paper the kinetics of the formation of nanoparticles in microemulsions is studied by Monte Carlo computer simulation. It is observed that compartmentalization of the reactants induces a separation of the nucleation and growth processes, which is more clearly observed when the concentration of reactants is relatively high. It is also observed that growth by autocatalysis and by ripening overlaps at low concentrations but occurs on different time scales at high concentration. A comparison between the results of these simulations and those from Smoluchowski's rapid-coagulation mechanism is made, showing that this theory is adequate to model the kinetics of these reactions.