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Effet Leslie chimique dans les monocouches de Langmuir et les films libres de smectique C chiraux

Abstract : This thesis is focused on the Leslie effect in thin films of chiral liquid crystals. Two systems are considered : Langmuir monolayers where the molecules form a bidimensional nematic, and free-standing films of smectic C*. This out-of-equilibrium effect couples a flux of foreign molecules with the rotation of the liquid crystal molecules. It also manifests itsef with flows in the layers. This effect is the result of two coupling coefficients -chemo-mechanical and chemo-hydrodynamical- which are rigorously defined in this work.In Langmuir monolayers, the Leslie effect is caused by the evaporation of the water molecules from the subphase. To study this system, we have developed new experimental techniques using an electric field and a humidifier to prepare large monodomains in which the molecules can freely rotate. We also designed six independent experiments to precisely measure the four material constants including the chemo-mechanical Leslie coefficient. Note that there are no flows -and thus no chemo-hydrodynamical effects- in monolayers because of the high viscosity of the subphase.For our study of free standing-films of smectic C*, we used a controled ethanol flux as the driving force of the Leslie effect.In these experiments, strong flows are observed in addition to the rotation of the molecules. These flows dominate the dynamics of the film when a disclination of strength +1 is located in the center of the film, which leads to a discrete set of solutions. These results are theoretically explained in the framework of the Leslie theory with numerical simulations and the orders of magnitude of both the chemo-mechanical and chemo-hydrodynamical Leslie coefficients are given.
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Submitted on : Tuesday, September 14, 2021 - 6:24:17 PM
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  • HAL Id : tel-03344260, version 1

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Félix Bunel. Effet Leslie chimique dans les monocouches de Langmuir et les films libres de smectique C chiraux. Matière Molle [cond-mat.soft]. Université de Lyon, 2021. Français. ⟨NNT : 2021LYSEN028⟩. ⟨tel-03344260⟩

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