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Insight in shear banding under transient flow.
J P Decruppe1, S Lerouge, J F Berret
1Groupe Rhéophysique des Colloïdes, Laboratoire de Physique des Liquides et Interfaces, Université de Metz, 1 Boulevard François Arago, 57078 Metz, France.
Summary
This study investigates surfactant solutions under shear flow, observing stress overshoots and oscillations. A distinct anisotropic layer forms near the wall, revealing complex rheo-optical dynamics.
Area of Science:
- Rheology
- Soft Matter Physics
- Physical Chemistry
Background:
- Understanding the complex flow behavior of viscoelastic fluids like surfactant solutions is crucial.
- Transient shear flows induce dynamic structural changes and stress responses in these materials.
Purpose of the Study:
- To investigate the rheo-optical properties of a viscoelastic surfactant solution under transient shear flow.
- To characterize the evolution of shear stress, transmitted light intensity, and scattering patterns during flow cessation and relaxation.
Main Methods:
- Applying a step-shear rate to a viscoelastic surfactant solution.
- Monitoring transient shear stress (sigma), transmitted light intensity (I(t)), and scattering patterns.
- Observing the formation and characteristics of an anisotropic layer near the wall using laser diffraction.
Main Results:
- Observed significant shear stress overshoots followed by damped oscillations and a sigmoidal relaxation process.
- Detected enhanced concentration fluctuations via diffusion patterns during the initial flow phase.
- Identified a fine anisotropic layer near the moving wall, developing after the relaxation phase, with subbands approximately 100 micrometers wide.
Conclusions:
- Transient shear flow triggers complex rheological and optical responses in surfactant solutions.
- The formation of an anisotropic wall layer is a delayed phenomenon, indicating significant structural reorganization.
- Rheo-optical measurements provide insights into microstructural evolution and dynamics in complex fluids.