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Comportement infrarouge de milieux hétérogènes : mesure et restitution par différentes techniques d’homogénéisation

Abstract : Due to their original properties related to their spatial structuration, nanocomposites are attracting a great interest in materials science. Their optical properties can be adapted by adjusting concentrations, sizes, shapes, and component materials. Despite this potential, their study is still relatively complex; the impact of the appearance and spatial distribution of heterogeneities on their response is still misunderstood today. The Bergman's representation allows to respond to numerous questions . This theory is applicable only for homogenizable systems, typically for the small particles. Nevertheless, we show here that collective effects between heterogeneities are susceptible to make this condition insufficient. The aim of this thesis is to develop a methodology based on Bergman's theory, combining numerical tools and experimental tools to finely characterize the optical and structural properties of heterogeneous media. Synthetic nanocomposites have allowed to validate the methodology. The results show that the shape of the spectral density is less sensitive for vitreous materials than for crystalline materials because of their large absorption bands. The generalization of the methodology on more complex materials has allowed on the one hand to recover the dielectric function and the spectral density function of compacted powders of silica nanoparticles; on the other hand, to identify the chemical composition of the nanophases present in the demixed zinc gallogermanate glasses.
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Submitted on : Thursday, April 14, 2022 - 3:33:10 PM
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Alima Nzie. Comportement infrarouge de milieux hétérogènes : mesure et restitution par différentes techniques d’homogénéisation. Science des matériaux [cond-mat.mtrl-sci]. Université d'Orléans, 2021. Français. ⟨NNT : 2021ORLE3132⟩. ⟨tel-03641850⟩

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