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Theses

Couches poreuses de silice structurées par des latex : structure, propriétés mécaniques et applications optiques

Abstract : Thin films with low-refractive index are of great interest to adjust the optical properties of optical components, e.g. reflectivity. In this respect, mesoporous sol-gel silica films prepared by surfactant self-assembly have been extensively studied but show poor refractive index stability as capillary condensation of atmospheric water can occur in the pores. To tackle this issue, we successfully prepared sol-gel porous silica films, templated by custom-made latex, with pore size above 30 nm insensitive to capillary condensation. The absence of significant microporosity in the silica walls allows us to independently and accurately tailor pore size, volume fraction and surface chemistry. Pore structure as a function of pore size and porous fraction was assessed by ellipsometry-porosimetry and positron annihilation: a percolation transition of the pore network at decreasing volume fraction was shown. The position of the pore occlusion threshold is interpreted in the scope of a continuum percolation model. Mechanical properties were investigated with nanoindentation: Young's modulus and hardness were shown to follow a minimal area model with porous fraction while no effect of pore size was measured. The model behavior observed both for pore structure and mechanical properties opens the way to further optimization of the properties of the porous material. These new films show very stable low refractive index, especially when the porosity is closed. As their refractive index can be tuned in a large range (from 1.15 to 1.40 at 600 nm), they appear as very promising for optical applications.
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Contributor : François Guillemot <>
Submitted on : Monday, December 6, 2010 - 4:43:59 PM
Last modification on : Wednesday, May 15, 2019 - 4:09:16 AM
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  • HAL Id : pastel-00543809, version 1

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François Guillemot. Couches poreuses de silice structurées par des latex : structure, propriétés mécaniques et applications optiques. Matériaux. Ecole Polytechnique X, 2010. Français. ⟨pastel-00543809⟩

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