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Theses

Effet de l'ancrage sur les propriétés d'un cristal liquide Antiferroélectrique confiné en cellule mince

Abstract : The influence of boundary conditions on macroscopic properties of antiferroelectric liquid crystal cells were studied in 2µm thick planar samples of MHPOBC. The special attention was paid to the transition ferro-antiferroelectric phase. A theoretical analysis shows that in the antiferroelectric phase, ferroelectric (FE) and antiferroelectric (AF) anchorings can be realized (at the same temperature) on the glass plate surface, while in the ferroelectric phase only ferroelectric anchoring is allowed. It means, that we can obtain in some temperature interval in the antiferroelectric phase four different structures (states) combining anchorings on both upper-lower glasses : 1) FE-FE, 2) AF-AF, 3) AF-FE, 4) FE-AF. Two later structures are called mixed structures (states) and are obtained from both homogeneous states by applying an electric impulsion.
In the thesis three experimental methods were used to proof the existence of the mixed state. Namely 1) electro-optical spectroscopy with rotating sample (scanning electro-optical spectroscopy), 2) switching current measurements at extremely low frequencies (from 20mHz) and 3) pyroelectric measurements. The results obtained by these tree methods are complementary and clearly confirm the existents of mixed states.
In the switching experiment the influence of ionic current is important. Therefore one part of the thesis is devoted to the study of ions.
The results of pyroelectric measurements confirm so cooled “surface electroclinic effect” which is observable in the SmA phase close to the transition to the ferroelectric phase. This effect is also an example of the influence of boundary conditions on the sample properties in thin cells.
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https://tel.archives-ouvertes.fr/tel-00009771
Contributor : Julien da Sylva <>
Submitted on : Monday, July 18, 2005 - 6:27:33 PM
Last modification on : Wednesday, April 17, 2019 - 1:19:10 AM
Long-term archiving on: : Friday, April 2, 2010 - 10:35:04 PM

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  • HAL Id : tel-00009771, version 1

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Julien da Sylva. Effet de l'ancrage sur les propriétés d'un cristal liquide Antiferroélectrique confiné en cellule mince. Physique [physics]. Université de Picardie Jules Verne, 2005. Français. ⟨tel-00009771⟩

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