Self-assembled water-in-oil (W/O)
microemulsions have been reported
as a suitable route for synthesis of size-controlled nanoparticles.
However, the mechanism of formation of nanoparticles in microemulsions
is still not completely understood. In this work, gold nanoparticles
(GNPs) were synthesized via the W/O microemulsion route. As the molar
ratio of water and dioctyl sodium sulphosuccinate (AOT) (R) increased from 2.5 to 5.0 to 7.5, the corresponding water drop
diameter increased from 2.7 to 5.0 to 7.3 nm. In parallel, the mean
hydrodynamic diameter of GNPs increased from 6.5 to 11.3 to 15.6 nm
for corresponding R values of 2.5, 5.0, and 7.5.
Therefore, although there is a monotonically increasing trend of the
mean diameter of GNPs with the initial drop diameter, for all values
of R, the mean diameter of GNPs was significantly
higher than the initial drop diameter. Consequently, previously known
simulation vastly underpredicts the experimental GNP diameter. However,
only on redefining the particle–particle coagulation event
(during coalescence of microemulsion drops containing particles) does
the current kinetic Monte Carlo (kMC) simulation agree well with the
experimental results. In addition, we also find that the coagulation
efficiency of solid nanoparticles (βp) increases
with R, and βp is lesser than the
coalescence efficiency of liquid drops (βd) over
the range of R values concerned. Hence, a combined
simulation and experimental study enumerates the dynamics of size
evolution of nanoparticles and the events involved in their formation
in a W/O microemulsion system.