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Flow phase diagrams for concentration-coupled shear banding
1Polymer IRC and Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK. physf@irc.leeds.ac.uk
The European Physical Journal. E, Soft Matter
|March 12, 2004
Summary
This study models concentration coupling in wormlike micellar systems using the Johnson-Segalman model. It reveals how shear banding behavior and flow phase diagrams change with concentration, identifying a critical point for shear banding.
Area of Science:
- Soft Matter Physics
- Rheology
- Surfactant Science
Background:
- Shear banding in wormlike micellar systems is a complex phenomenon influenced by concentration.
- Experimental evidence suggests concentration coupling plays a crucial role in this process.
- Understanding shear banding requires accurate theoretical models that capture macroscopic flow behavior.
Purpose of the Study:
- To calculate flow phase diagrams for wormlike micellar systems using a two-fluid, non-local Johnson-Segalman model (d-JS-phi).
- To investigate the influence of concentration on shear banding and macroscopic flow curves.
- To identify the non-equilibrium critical point where shear banding terminates.
Main Methods:
- Utilized the two-fluid, non-local Johnson-Segalman (d-JS-phi) model to simulate shear banding.
- Calculated macroscopic flow curves (Sigma(gamma,phi)) across a range of concentrations (phi).
- Analyzed the dependence of phase diagrams and flow curves on the ratio of spatial gradient lengths (r = l/xi).
Main Results:
- Flow phase diagrams and flow curves were computed, showing a characteristic kink and a sloping plateau at sufficient concentrations.
- A non-equilibrium critical point ([Sigmac,phic,gammac]) was identified where the shear banding coexistence regime vanishes as concentration decreases.
- The model demonstrates that phase diagrams and flow curves are sensitive to the ratio of characteristic lengths (l/xi), impacting state selection.
Conclusions:
- The d-JS-phi model successfully reproduces key features of shear banding in wormlike micellar systems, including the coexistence regime and critical point.
- The study provides a framework for reconstructing flow phase diagrams from experimental flow curves, aiding in the validation of concentration difference measurements.
- The ratio of interfacial gradient lengths significantly influences the model's predictions, highlighting its importance in describing shear band interfaces.