On the Investigation of the Droplet-Droplet AOT Reverse Micellar Interaction upon Changing the External Solvent Composition and, its Impact on Gold Nanoparticles Synthesis

JORGE A GUTIERREZ; R DARIO FALCONE; M ARTURO LOPEZ QUINTELA; DAVID BUCETA; JUANA J SILBER; N MARIANO CORREA*

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2014 p. 2095 - 2102

1434-1948

The effect of the composition of the nonpolar organic media on the 1,4-bis-2-ethylhexylsulfosuccinate (AOT) reverse micelles (RMs) properties 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 absorption and emission probe was studied while the droplet sizes, were measured by dynamic light scattering (DLS).             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 inter-droplet attractive interactions and the droplet sizes also increases. With C343 spectroscopy we were able to determine the ?operational? critical micellar concentration, the RMs interfacial micropolarity, the hydrogen bond ability of the media and the sequestrated water structure in every RMs studied.             To verify the modulation of the inter-droplet interactions by the external solvent we have used a well-known synthetic method to create gold nanoparticles in different RMs media. The results support the conclusions that using n-heptane as a nonpolar solvent the droplet-droplet interactions are favored. Thus, the rate of material exchange among micelles increases, and hence, small, monodispersed and highly concentrated gold nanoparticles are formed. The situation is different for AOT RMs prepared in benzene where subnanometer gold clusters are produced. The formation of clusters instead of nanoparticles reflects a poor material exchange among micelles due to unfavorable droplet-droplet interactions. In this way, our results offer a new appealing way to focus the production of nanoparticles into sub-nanometer clusters, which is one of the hottest topics nowadays in nanoparticle synthesis.             Therefore, it is possible to dramatically affect different RMs properties by changing the solvent blend, which cannot be obtained using only single solvent composition, and which may have a high impact on nanotechnology. We anticipate remarkable effect on nanoparticle sizes and polydispersity when working with different organic solvent blend composition.