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Dynamique des dislocations coin et dissipation dans les films librement suspendus de cristal liquide smectique

Abstract : Free-standing liquid crystal (8CB) smectic-A films are very stable due to the elasticity of the lamellar structure and can support the capillary pressure imposed by the meniscus bordering the film. This meniscus acts as a reservoir that supplies material to the film. The subject of this thesis is to study the dynamics and the associated dissipative processes that occur in smectic films. Particular attention is
focused on the finite permeability of the meniscus.

We find that when the exchange of matter between the film and the meniscus is slow, the dissipative behavior is controlled by the permeation flows around edge dislocations within the meniscus. Our hydrodynamic model shows that the dissipation takes place at the entrance of the meniscus, where the smectic layers are well-oriented, and it strongly depends on the film thickness. Complimentary experiments on the growth dynamics of dislocation
loops observed in thin films, and the pressure equilibration of two menisci connected by thick films, have both confirmed experimentally this model.

Bubble collapse dynamics have allowed us to characterize the dissipation for faster flow regimes. Our experiments have showed that after a first step, wherein the lamellar structure of the meniscus is destroyed, there is an increase in the meniscus permeability. This increase leads to bubble collapse during which matter penetrates into the meniscus with shear thining behavior. We also observe that the nucleation and growth of thick-film islands, within thin films, tend to make the dynamic processes less dissipative.
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Contributor : François Caillier <>
Submitted on : Thursday, December 8, 2005 - 7:00:26 PM
Last modification on : Wednesday, November 20, 2019 - 2:59:30 AM
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  • HAL Id : tel-00011175, version 1

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François Caillier. Dynamique des dislocations coin et dissipation dans les films librement suspendus de cristal liquide smectique. Analyse de données, Statistiques et Probabilités [physics.data-an]. Ecole normale supérieure de lyon - ENS LYON, 2005. Français. ⟨tel-00011175⟩

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