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Contribution rhéologique et optique à l'étude expérimentale de transitions induites par cisaillement dans des solutions micellaires

Abstract : Micellar solutions form materials which able present a great variety of behaviour. This work presents the action of a shear, which creates order, on theses systems. Mixtures used are solutions of cetyltrymethylammonium bromide (CTAB) with and without salt (KBr) i.e. in which case the electrostatic interactions are not screened. Measurements experiments were carried out with a rheometer (constant shear stress mode with cone-plan geometry) and with a flow birefringence device (couette flow). Concentrations of screened system CTAB/KBr are selected so that they are far from nematic phase at rest. Shear can induce isotropic/nematic (I/N) transition as the velocity gradient becomes greater than a critical value. Measurements of flow birefringence show two phases co-exist in the gap, the nematic phase being located near to the moving inner cylinder. The study of the second, salt free aqueous CTAB solutions, shows significant differences in comparison with the screened system. The zero shear viscosity N0 is very dependant on concentration and the system is characterized by a spectrum of relaxation times. In non-newtonian domain, the rheological and optical experiments shown a I/N transition under shear as well as the existence of biphasic domain when the shear rate is ranging from two critical shear rates. We analyse lastly the "perturbations" of the isotropic concentrated solution of CTAB without addition of salt after being subjected to sufficiently high shear stress to induce nematic phase. In particular, we present the results of rhelogical measurements showing the evolution of shifting N/I temperature transition under shear, bringing to the fore a kind of "memory" effet
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Submitted on : Tuesday, April 24, 2018 - 4:11:24 PM
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Emmanuel Cappelaere. Contribution rhéologique et optique à l'étude expérimentale de transitions induites par cisaillement dans des solutions micellaires. Sciences de l'ingénieur [physics]. Université Paul Verlaine - Metz, 1996. Français. ⟨NNT : 1996METZ001S⟩. ⟨tel-01777104⟩



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