Physicochemical investigation of surfactant-coated gold nanoparticles synthesized in the confined space of dry reversed micelles

Gold nanoparticle/surfactant composites have been synthesized by a novel reduction reaction in the confined space of dry sodium bis(2- ethylhexyl)sulfosuccinate (AOT) or lecithin reversed micelles dispersed in n-heptane and cyclohexane, respectively. The reaction was carried out by adding an opportune amount of anhydrous hydrazine/tetrahydrofuran solution to a suspension of HAuCl4-containing dry reversed micelles dispersed in organic solvent. UV-vis investigation ascertained the formation of stable metal gold nanoparticles and the analysis of FT-IR spectra highlighted the formation of an oriented surfactant monolayer at the nanoparticle surface. Simple evaporation under vacuum of the organic solvent leads to the preparation of very interesting gold nanoparticle/surfactant liquid crystal composites. Such nanocomposites, characterized by WAXS and SAXS, showed the presence of small (radius~14A° ) and stable gold nanoparticles dispersed in the surfactantmatrix. It has been also emphasized that a simple washing process with ethanol is a suitable method to eliminate the excess of surfactant leaving a novel nanomaterial constituted by gold nanoparticles coated by a monolayer of opportunely oriented surfactant molecules.