Suivi in situ de la nucléation-croissance de nanoparticules d'or

Benjamin Abécassis 1
1 LIONS - Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : In this thesis, we assess the formation mecanism of gold nanoparticles in situ in liquid media (homogeneous or in microemulsion) by small angle scattering techniques. The first part details several important concepts which are useful for an appropriate understanding of the rest of the thesis along with an overview of the literature on the subject. We then present results of time resolved synchrotron small angle X ray scattering and UV-visible experiments performed in situ during the formation of gold nanoparticles in organic solvent. We show that it is possible to follow the nucleation and growth of the particles in real time with a time resolution of a few hundreds milliseconds. We show that depending on the chemical nature of the ligand the nucleation and growth can be either simultaneous or separated in time. In the latter cas, the growth is limited by surface reaction of the monomer at the particle's surface. We also show that when the produced nanoparticles have an average radius larger than 5 nm, they self-assemble into ordered super-lattices which exhibit a face centered cubic cristallographic structure. In a third part, by using a combination of complementary techniques we study water/oil/octylammoniumoctanoate microemulsions in the reverse micelles part of the phase diagram. The structure of these “catanionic“ microemulsions are revealed as a function of the water content, the temperature and the surface charge. The different observed topologies (sphere, rodlike or connected wormlike) and the phase transitions are compared to a recent theory which takes into account the curvature energy of the surfactant film. Finally, we show that these microemulsions can be used efficiently to synthesise gold nanoparticles. We show that the template effect, often cited to explain the formation of nanoparticles in reverse micelles is, in our case, not relevant. It is also noteworthy possible to separate and purify the as-produced nanoparticles by slightly reducing the temperature thanks to the original phase behaviour of these catanionic microemulsions.
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Benjamin Abécassis. Suivi in situ de la nucléation-croissance de nanoparticules d'or. Matière Molle [cond-mat.soft]. Ecole Polytechnique X, 2006. Français. ⟨tel-00285508⟩

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