Skip to Main content Skip to Navigation
Theses

Etude de l'interface lamellaire-éponge des systèmes lyotropes gonflés : du facettage volumique et des formes de croissance aux modèles microscopiques

Abstract : This dissertation treats different properties of the interface between two swollen phases of membranes: the lamellar La and the sponge L3 phases. The lamellar phase is made of bilayers and displays a smectic order whereas the sponge phase is made of a bicontinuous and disordered membrane. L3 phase is a fluid an isotropic phase at large scale. The main focus is set on the patterns and instabilities that arise in the two-phase region.
In a first experimental part, the author characterizes the anisotropy of the La-L3 interface tension sigma and shows the existence of a preferred orientation theta for the La bilayers at the interface. Due to the softness of the La layers, the anchoring conditions give rise to macroscopic defects by a mechanism close to the “bulk faceting” of thermotropic SmA materials. This phenomenon is thoroughly studied in two cases :
* the free growth of La germs in the isotropic sponge phase
* the formation of regular lattices of macroscopic defects in thin La slabs confined between glass (homeotropic anchoring) and the sponge phase (preferred orientation theta).
In order to interpret the observed textures, the author introduces the notion of curved wall defects and thus extends the geometrical description of smectics. The importance of these curved walls in the textures of smectics in contact with fluids, that is the smectics submitted to an “orientational anchoring”. This work on textures is completed by a study of the growth instabilities of complex La droplets in the isotropic L3 phase. A coupling between the solid-like growth mechanism (dendrites ....) and the bulk faceting is evidenced and discussed. This part greatly clarified the classic topic about the growth a SmA nuclei (the so-called “bâtonnets”).
In a last part, the author discusses several microscopic models for the La-L3 interface that could explain its unusual macroscopic properties. In particular, a simple model of epitaxy between the two membrane phases predicts the value of theta,, the properties and magnitude of sigma(theta), and the possibility of a transition for the main. Anchoring. This last point is checked by using ferrolyotropic systems, in wich the elastic constants can be tuned.
Complete list of metadatas

Cited literature [117 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-00003193
Contributor : Christophe Blanc <>
Submitted on : Monday, July 28, 2003 - 12:55:15 PM
Last modification on : Wednesday, December 9, 2020 - 3:05:25 PM
Long-term archiving on: : Friday, April 2, 2010 - 7:22:48 PM

Identifiers

  • HAL Id : tel-00003193, version 1

Citation

Christophe Blanc. Etude de l'interface lamellaire-éponge des systèmes lyotropes gonflés : du facettage volumique et des formes de croissance aux modèles microscopiques. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Pierre et Marie Curie - Paris VI, 2000. Français. ⟨tel-00003193⟩

Share

Metrics

Record views

390

Files downloads

477