the Investigation of the Droplet- Droplet Interactions of Sodium 1,4-Bis( 2-ethylhexyl) Sulfosuccinate Reverse Micelles upon Changing the External Solvent Composition and Their Impact on Gold Nanoparticle Synthesis

The effect of the composition of the nonpolar organic media on the properties of sodium 1,4-bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles (RMs) at a fixed temperature were investigated. To monitor interfacial micropolarity and sequestrated water structure in n-heptane:benzene/AOT/water RMs, the solvatochromic behavior of coumarin 343 (C343) as an absorption and emission probe was studied, and the size of the droplets was measured by dynamic light scattering (DLS). The DLS results confirm the formation of the n-heptane:benzene/AOT/water RMs at every n-heptane mole fraction investigated. The data show that as the n-heptane content increases, the interdroplet attractive interactions and the droplet size both increase. With C343 spectroscopy, we determined the operational critical micellar concentration, the interfacial micropolarity of the RMs, the hydrogen-bond ability of the media, and the sequestrated water structure in every RM system studied. To verify the modulation of the interdroplet interactions by the external solvent, we have used a well-known synthetic method to create gold nanoparticles in different RM media. The results support the conclusion that the droplet-droplet interactions are favored with n-heptane as the nonpolar solvent. Thus, the rate of material exchange among micelles increases, and small, monodispersed, and highly concentrated gold nanoparticles are formed. The situation is different for AOT RMs prepared in benzene, in which subnanometer gold clusters are produced. The formation of clusters instead of nanoparticles reflects poor material exchange among the micelles owing to unfavorable droplet-droplet interactions. In this way, our results offer a new appealing way to focus the production of nanoparticles into subnanometer clusters, which is one of the hottest current topics in nanoparticle synthesis. Therefore, it is possible to dramatically affect different properties of the RMs by changing the solvent blend; such effects cannot be obtained with only a single solvent composition and may have a large impact on nanotechnology. We anticipate remarkable effects on nanoparticle sizes and polydispersity with different organic solvent blends.