On 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

Abstract

The effect of the composition of the nonpolar organic mediaon the properties of sodium 1,4-bis(2-ethylhexyl) sulfosuccin-ate (AOT) reverse micelles (RMs) at a fixed temperaturewere investigated. To monitor interfacial micropolarity andsequestrated water structure inn-heptane:benzene/AOT/water RMs, the solvatochromic behavior of coumarin 343(C343) as an absorption and emission probe was studied, andthe size of the droplets was measured by dynamic light scat-tering (DLS). The DLS results confirm the formation of then-heptane:benzene/AOT/water RMs at everyn-heptane molefraction investigated. The data show that as then-heptanecontent increases, the interdroplet attractive interactions andthe droplet size both increase. With C343 spectroscopy, wedetermined the “operational” critical micellar concentration,the interfacial micropolarity of the RMs, the hydrogen-bondability of the media, and the sequestrated water structure inevery RM system studied. To verify the modulation of theinterdroplet interactions by the external solvent, we haveused a well-known synthetic method to create gold nanopar-IntroductionReverse micelles (RMs) are of considerable practical im-portance in different areas such as detergents, foodstuffs,and cosmetics.[1,2]RMs are supramolecular assembliesformed when surfactants are dissolved in nonpolar organicsolvents. Their polar area is located in the interior (core),and their hydrocarbon tails extend into the organic non-polar solvent.[1,3,4]Different anionic, cationic, and nonionic[a] Departamento de Química, Universidad Nacional de RíoCuarto,Agencia Postal # 3, C. P. X5804BYA Río Cuarto, ArgentinaE-mail: mcorrea@exa.unrc.edu.arhttp://gso-unrc.blogspot.com.ar/www.unrc.edu.ar[b] Facultad de Química, Departamento de Química-Física,Laboratorio de Nanotecnología y Magnetismo (NANOMAG),Universidad de Santiago de Compostela,C. P. 15782 Santiago de Compostela, SpainSupporting information for this article is available on theWWW under http://dx.doi.org/10.1002/ejic.201301612.Eur. J. Inorg. Chem.2014, 2095–2102© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim2095ticles in different RM media. The results support the conclu-sion that the droplet–droplet interactions are favored withn-heptane as the nonpolar solvent. Thus, the rate of materialexchange among micelles increases, and small, monodis-persed, and highly concentrated gold nanoparticles areformed. The situation is different for AOT RMs prepared inbenzene, in which subnanometer gold clusters are produced.The formation of clusters instead of nanoparticles reflectspoor material exchange among the micelles owing to unfa-vorable droplet–droplet interactions. In this way, our resultsoffer a new appealing way to focus the production of nano-particles into subnanometer clusters, which is one of the hot-test current topics in nanoparticle synthesis. Therefore, it ispossible to dramatically affect different properties of the RMsby changing the solvent blend; such effects cannot be ob-tained with only a single solvent composition and may havea large impact on nanotechnology. We anticipate remarkableeffects on nanoparticle sizes and polydispersity with differentorganic solvent blends.