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College Park, Maryland      June 6 - 10 , 2004

WP78: Neutron spin echo study of AOT reverse micelles with application to metallic nanoparticle synthesis and compressible fluids

Christopher L. Kitchens and Christopher B. Roberts (Department of Chemical Engineering, Auburn University, AL 36830), Dobrin Bossev (University of Maryland, College Park; National Institute of Standards and Technology)

The common surfactant, AOT (Sodium bis-2-ethylhexyl-sulfosuccinate), forms thermodynamically stable water-in-oil microemulsions containing self-assembled spherical reverse micelles. The reverse micelles consist of a small water pools encased in an AOT surfactant monolayer and dispersed within a bulk organic fluid. The nanometer sized water core acts as a “nano-reactor” for aqueous phase reactions, eg. metallic nanoparticle synthesis within the micelle cores. It has been demonstrated that the metallic nanoparticle growth rate and the average particle size synthesized are influenced by the size of the reverse micelle, represented by W where W=[H2O]/[AOT] and the thermophysical properties of the bulk alkane solvent, specifically the solvent interactions with the surfactant tails. Studies of reverse micelle dynamics in solution have shown that adjustable parameters such as the bulk solvent properties and W influence the intermicellar exchange rate. In this work, we propose to use Small Angle Neutron Scattering (SANS) correlated with Neutron Spin Echo (NSE) Spectroscopy to study reverse micelle dynamics as a function of the bulk d-alkane solvent and the size of the reverse micelles. NSE offers the unique ability to perform dynamic measurements of thermally induced shape fluctuation in the AOT surfactant monolayer, however the time averaged, static SANS measurements are necessary to obtain pertinent information from the dynamic system, specifically the bending elastic modulus and saddle-splay elastic modulus.

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