(166j) Gold Nanoparticle Formation in Water-in-Oil Microemulsions:Experiment and Simulation

Self-assembled, surfactant templated microreactors, such as water in oil (W/O) microemulsions, have been reported as a suitable route for synthesis of controlled size nanoparticles. These microemulsions are thermodynamically stable, nanoscale droplets of water dispersed in a continuous oil phase. The main advantage of microemulsion is that the drop size can be easily tuned to get the desired particle size. However, the mechanism of formation of nanoparticles in microemulsion is still open for discussion. In this work, gold nanoparticles (GNPs) were synthesized via W/O microemulsion route. As the molar ratio of water to isooctane (R) was increased from 2.5 to 5.0 to 7.5, its corresponding drop diameter increased from 2.7 to 5.0 to 7.3 nm, respectively. The mean diameter of GNPs simultaneously increased from 6.5 to 11.3 to 15.6 nm, for correspondingly increasing values of R, i.e., 2.5 to 5.0 to 7.5, respectively. Thus, for all values of R, the average diameter of the GNPs was significantly larger than the initial droplet size. It is clear that, existing kinetic Monte Carlo (kMC) simulation underpredicts experimental results. However, only on including coalescence of drops during particle coagulation event, the current kMC simulation agrees well with the experimental results. We also find that, coagulation efficiency (β_p) increases with R, implying larger drops coalesce more easily. Hence, a combined study of simulation and experiment enumerates the dynamics of size evolution of nanoparticles and the events involved in the formation of nanoparticles in W/O microemulsions (Figure).