Microstructural evolution of a model, shear-banding micellar solution during shear startup and cessation

Area of Science:

• Complex Fluids
• Rheology
• Materials Science

Background:

• Shear banding in entangled wormlike micelles is a complex phenomenon.
• Understanding the microstructural evolution during flow is crucial for explaining this behavior.

Purpose of the Study:

• To directly measure the microstructural evolution of polymerlike micelle solutions during flow startup and cessation.
• To provide a quantitative understanding of shear banding mechanisms in these systems.

Main Methods:

• Direct measurements of segmental-level microstructure.
• In-situ observation during flow startup and cessation in the plane of flow.

Main Results:

• Observed distinct stages during flow startup, including elastic response, stress overshoot, and homogeneous flow with micellar alignment.
• Identified shear band formation with coexisting flow-aligned and isotropic bands.
• Characterized nontrivial relaxation dynamics upon flow cessation.

Conclusions:

• Resolved controversy regarding shear banding mechanisms in entangled wormlike micelles.
• Provided insights into shear-banding instabilities in related complex fluid systems.
• Demonstrated the utility of the methods for exploring complex fluid rheology and constitutive equations.