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Transition vitreuse de nanoparticules magnétiques en interaction

Abstract : This PhD work is an experimental study of glass transitions in colloidal dispersions of charged and magnetic nanoparticles (ferrofluids).
- The colloidal glass transition, observed at high concentrations, leads to an amorphous solid state out of the thermodynamical equilibrium. The charged particles are then strongly interacting, in a potential where the electrostatic repulsions prevail. Thanks to the original properties of ferrofluids, the complete structural degrees of freedom of the particles are considered. Positional ones are probed using static and dynamical scattering techniques (X-rays and neutrons). Glassy dynamics (non diffusivity, aging and intermittency) are reported at nanometric lengthscales. When a magnetic field is applied, the structure of the dispersion becomes anisotropic, as well as the translational dynamics of the particles and its aging. The rotational dynamics of the nanoparticles are probed using magneto-induced birefringence measurements. The rotational dynamics drastically slow down from a volume fraction threshold which depends on the intensity of the repulsions between particles. Its aging is studied on long time scales. An effective age is introduced to unite aging properties at different concentrations.
- At low temperatures, the frozen dispersion constitute an assembly of disordered giant spins, which present some analogies with atomic spin glasses. Using SQUID magnetometry, we study the orientational dynamics of these superspins. We use a method borrowed from spin glasses to extract a dynamical correlation length between superspins; its size increases during the aging.
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https://tel.archives-ouvertes.fr/tel-00193960
Contributor : Elie Wandersman <>
Submitted on : Wednesday, December 5, 2007 - 11:24:19 AM
Last modification on : Wednesday, December 9, 2020 - 3:12:50 PM
Long-term archiving on: : Monday, April 12, 2010 - 6:11:03 AM

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  • HAL Id : tel-00193960, version 1

Citation

Elie Wandersman. Transition vitreuse de nanoparticules magnétiques en interaction. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Pierre et Marie Curie - Paris VI, 2007. Français. ⟨tel-00193960⟩

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