Contribution à l'étude expérimentale du rhéoépaississement et des transitions induites sous écoulements dans des solutions micellaires

Abstract : The aim of this work was to study the behaviour of aqueous micellar solutions under shear. We used rheology and, to obtain complementary results, preliminary experiments of flow birefringence and small-angle neutron scaterring. We used solutions of a cationic surfactant, the cetyltrimethylammonium bromide, to which we added different salts (simple or organic). Two class of behaviours have been observed and carrefully studied : the solutions have exhibited, with very restricted conditions, shear thickening (the viscosity rises with the shear rate). This phenomenon is caused by the creation of shear induced structures. The exact nature of these structures remains to be defined. However, the obtained results have shown that those were large anisotropic structures, strongly oriented under flow, as confirmed by our measurements of flow birefringence and small-angle neutron scattering ; in other circumstances, a decrease of the apparent viscosity versus the shear rate has also been observed. This evolution corresponds to orientation phenomena connected with possible deformations. A very interesting particular case of shear thinning corresponds to the presence of a shear plateau (constant shear stress against shear rate) with appearence of shear banding structures, which could be explained by true mechanical instabilities or the existence of phase transisitions induced by shear. We have compared our obtained results with the theorical predictions of Cates. During this work, we have also realized an elongational flow birefringence device with a four roll cell generating a plane hyperbolic flow field. We have given preliminary results obtained with different micellar solutions (relative to the uniformity of the field and saturation of the induced flow birefringence). Other systematic studies with other techniques will be necessary to understand the real mechanisms occuring and the exact nature of the induced structures in the different situations
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Valérie Hartmann. Contribution à l'étude expérimentale du rhéoépaississement et des transitions induites sous écoulements dans des solutions micellaires. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1997. Français. ⟨NNT : 1997METZ050S⟩. ⟨tel-01777227⟩

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