Mechanism of formation of inorganic and organic nanoparticles from microemulsions.

This chapter essentially deals with the preparation of nanoparticles using microemulsions. The preparation of inorganic nanoparticles--Ni2B, Pt, Au, Pt-Au, AgX--and the synthesis of organic nanoparticles--cholesterol, rhovanil, rhodiarome--are systematically studied as a function of the concentration of the precursor molecules, the size of the inner water cores, and the manner of mixing the various solutions. Two different behaviors are observed in the various systems. The first case shows a dependence of the nanoparticle size on the various physicochemical parameters. Either a monotonous increase of the size or the presence of a minimum is observed as a function of the concentration of the precursor molecules. This case can be easily explained following the LaMer diagram, where the nucleation of the nanoparticles is separated from the particle growth. The second case does not show any dependence of the nanoparticle size on the physicochemical parameters. The size remains constant in all experimental conditions. The constant character of the size can be explained only by thermodynamic stabilization, where particles with a certain size are better stabilized. It should be emphasized that the size distribution is small in all the cases studied. Finally, the aging of the nanoparticles was also checked, especially for the organic nanoparticles. It is concluded that these particles remain stable for months in the microemulsion.