Instabilities of micellar systems under homogeneous and non-homogeneous flow conditions |
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Authors: | Arturo F Méndez-Sánchez M Rosario López-González V Hugo Rolón-Garrido José Pérez-González Lourdes de Vargas |
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Institution: | (1) Laboratorio de Reología, Departamento de Física, Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Apdo. Postal 75–685, C. P. 07300, México, D. F., México,;(2) Metalurgia y Materiales, Escuela Superior de Ingeniería Química e Industrias Extractivas, Instituto Politécnico Nacional, México, D. F., México, |
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Abstract: | The rheological behavior of a cetylpyridinium chloride 100 mmol l–1/sodium salicylate 60 mmol l–1 aqueous solution was studied in this work under homogeneous (cone and plate) and non-homogeneous flow conditions (vane-bob
and capillary rheometers), respectively. Instabilities consistent with non-monotonic flow curves were observed in all cases
and the solution exhibited similar behavior under the different flow conditions. Hysteresis and the sigmoidal flow curve suggested
as characteristic of systems that show constitutive instabilities were observed when running cycles of increasing and decreasing
stress or shear rate, respectively. This information, together with a detailed determination of steady states at shear stresses
close to the onset of the instabilities, allowed one to show unequivocally that "top and bottom jumping" are the mechanisms
to trigger the instabilities in this micellar system. It is shown in addition that there is not a true plateau region in between
the "top and bottom jumping". Finally, the flow behavior beyond the upturn seemed to be unstable and was found accompanied
by an apparent violation of the no-slip boundary condition. |
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Keywords: | Micellar solutions Flow instabilities Top and bottom jumping Slip Homogeneous and non-homogeneous flow |
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