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Title: Flow regimes of dilute surfactant solutions
Author: Macias, E.R.
Gonzalez, A.
Manero, O.
Gonzales-Nunez, R.
Soltero, J.F.A.
Attane, P.
Issue Date: 2001
Abstract: The shear-thickening of dilute surfactant solutions is investigated using water/cethyltrimethylammonium tosylate (CTAT) systems. We show that shear induced structures (SIS) are obtained in Couette and parallel-plate flows when the shear stress is higher than a critical shear stress, independently of the type of shear cell. Three different regimes are observed in Couette flow, confirming the results of Hu and co-workers on TTAA/NaSal/water systems. Flow regimes in parallel-plate flow geometries are studied with the aid of particle image velocimetry (PIV). Particular attention is paid to the calibration of the experimental set-up using pure water in order to distinguish between deviations of the rheometric velocity profile due to the onset of purely hydrodynamic instabilities from those due to the occurence of SIS. It is noteworthy that spatial and temporal fluctuations in the local velocity fields are observed when SIS exists, even when rheometric measurements show an apparently steady-state situation. When no SIS is present we found that the surfactant solutions behave like Newtonian fluids. Laminar secondary flows are present for both cells under the same conditions as those found for classical hydrodynamics. © 2001 Elsevier Science B.V. All rights reserved.
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