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Propriétés rhéophysiques d'un système micellaire viscoélastique : rhéoépaississement apparent et oscillations des contraintes

Abstract : We have studied rheological and optical properties of viscoelastic micellar solutions. We focus on a specific solution of CTAB/NaSal (50/100 mM), which shows, apparent shear-thickening in a narrow range of shear rates after a perfect plateau of shear stress characteristic of shear-banding. In this regime, in phase oscillations of the shear stress and of the first normal stress difference are recorded in a shearing device operating under controlled strain. The main goal of this work consists in finding correlations between rheological reponses, optical observations and ultrasonic velocimetry measurements in order to bring information on the mechanism which leads to the formation of these time periodic variations of shear stress. The direct observation of the annular gap of a Couette cell in a direction perpendicular to a plane containing the vorticity shows that the turbidity of the whole sample also undergoes time dependent variations with the same period as the shear stress; these variations are related to a periodic variations of the concentration of shear induced structures (SIS). However local velocity measurements reveal clearly the presence of slip at the walls of the Couette cell. In the shear-thickening regime, velocities present periodic fluctuations which probably induce shear stress oscillations.
Mots-clés : Rhéologie Biréfringence
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Houssain Azzouzi. Propriétés rhéophysiques d'un système micellaire viscoélastique : rhéoépaississement apparent et oscillations des contraintes. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 2005. Français. ⟨NNT : 2500METZ021S⟩. ⟨tel-01752386⟩

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