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Theses

Mouillage et orientation d'un film mince de cristal liquide colonnaire

Abstract : This thesis deals with columnar liquid crystal studied in the geometry of open supported thin films. Columnar liquid crystals are usually made of disk-shaped molecules derived from aromatic dyes. They are efficient charge transporters with the added capacity to self-assemble in large oriented domains. Consequently, such materials may be used in photovoltaic devices. In order to benefit from their good uniaxial charge mobility, their organization has to be controlled in uniform oriented thin films in the range of thicknesses of typically 100 nm. Homeotropic alignment (columns normal to the interface) is required for solar cells whereas uniaxial planar anchoring (columns parallel to the interface) is needed for applications such as polarizers or organic field effect transistor. Different methods to monitor the alignment in open thin films have been developed in this work, which make possible to achieve either homeotropic anchoring by a specific thermal treatment, or uniaxial planar orientation using a Teflon layer. Based on these orientation skills, a uniform ultra-thin film, free of dewetting and homeotropically oriented, is achieved (down to 50 nm thick) opening the way towards efficient solar cells, and a complete study of the optical properties has been performed (with the determination of the anisotropic complex indices) for different columnar liquid crystals. The dynamics of dewetting and the equilibrium state of a thin supported film have also been investigated. Experimental results show the formation of anisotropic droplets and reveal a nanometric film during dewetting.
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Emilie Charlet. Mouillage et orientation d'un film mince de cristal liquide colonnaire. Chimie théorique et/ou physique. Université Sciences et Technologies - Bordeaux I, 2008. Français. ⟨tel-00752187⟩

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