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Etude des propriétés électriques et optiques de cristaux liquides présentant des phases smectiques chirales et les phases frustrées SmQ et L.

Abstract : In a first part of this work, we studied the effect of the alkoxy chains length and the position of the fluor on the physical properties and on the sequence phases of a new monofluored LC series. As results, the SmC*A phase is destabilized, the temperature range of the SmC*alpha phase increased for the middle length chains but for the shorter one, only the SmA phase is present. The study of soft mode behaviour at low frequency together with the electric and optic results let us to establish the phase diagram (E, T) of a chosen compound. This allowed us to situate the ground phases and those induced by the field and well interpret the number of picks gotten in the electro-optic experiences. In a second part, we have reported on general characteristics of the L, SmQ and SmC*A phases in long and highly chiral compounds. The L phase is isotropic with a short range chiral and smectic order and presents an ORP whereas for the SmQ phase there is no ORP according to uniaxial character of the structure. In the SmC*A phase, the electro-optic properties of the ferroelectric induced phase are super-paraelectric type. In a last part, we studied the light propagation along the helical axis in the SmC* and SmC*A phases. The decomposition of the dielectric tensor in a new tensorial basis allowed us to find the two eingen modes of propagation.
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Mounir Manai. Etude des propriétés électriques et optiques de cristaux liquides présentant des phases smectiques chirales et les phases frustrées SmQ et L.. Matière Molle [cond-mat.soft]. Université Sciences et Technologies - Bordeaux I, 2006. Français. ⟨tel-00810488⟩

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