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Polymères Nématiques en peigne sous déformation: synthèse, rhéologie, conformation

Abstract : Nematic comb-like polymer under deformation : synthesis, rheology and conformation. Comb-like liquid-crystalline polymers gather the long-scale orientational properties of liquid crystals with mechanical properties of polymers. Therefore, these polymers rise a fundamental question: what are the influences of the comb-like structure and of the nematic interaction on the chain dynamics? To answer this question, we compared the properties of a linear polymer, a non-nematic and a nematic comb. At first, we determined the characteristics times, using classical rheology. Then, we studied the chain conformation relaxation after a uniaxial extension. The conformation can be described by two parameters: l, the global chain deformation and p, the number of locally relaxed monomers. For a linear polymer in a Rouse regime, l is the sample deformation and p grows as t1/2 (where t is the relaxation time). For the non-nematic comb, l remains constant but is smaller than the sample deformation and p grows as t. For the nematic comb, l decreases following a stretched exponential function of the rheological terminal time, whereas p remains constant. The isotropic comb dynamic is discussed in terms of living clusters made of temporary junctions between the teeth of the comb. In the nematic phase, the junctions life-time is strongly prolonged and the local relaxation is hindered. Therefore, the relaxation occurs from large scales! This study has been conducted associating rheology, X-ray scattering and small angle neutrons scattering. We have linked macroscopic properties to microscopic properties
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Véronique Demange-Fourmaux. Polymères Nématiques en peigne sous déformation: synthèse, rhéologie, conformation. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université Paris Sud - Paris XI, 1998. Français. ⟨tel-00002896⟩

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