Synthesis, size control, and passivation of US nanoparticles in water/AOT/n-heptane microemulsions

US nanoparticles have been synthesised by adding tetrabutylammonium hydrogen sulphide to water/sodium bis(2-ethylhexyl) sulfosuccinate/n-heptane microemulsions containing CdSO4. Analysis of UV-Vis absorption spectra recorded at various times indicates that an initial rapid formation of US nanoparticles is followed by a very slow growth process which can be well described by a power law. The growth process is totally inhibited by the addition of an appropriate amount of bis(2-ethylhexyl)amine (BEA) leading to the formation of stable nanosized US particles coated by an oriented monolayer of chemically bonded BEA molecules. Depending on the BEA addition time, the growth inhibition can be achieved at any moment of the process leading to an easy and fine size control. The main advantage of this procedure is that the BEA-coated US nanoparticles can be easily separated from the reaction medium and dispersed in nonpolar media such as heptane and in polar media such as an aqueous surfactant solution. (C) 2003 Elsevier Science B.V. All rights reserved.