Shear banding in soft glassy materials

Area of Science:

• Soft Matter Physics
• Rheology
• Materials Science

Background:

• Many soft materials (e.g., microgels, emulsions, liquid crystals) possess 'glassy' characteristics like structural disorder and metastability.
• These properties lead to distinct low-frequency shear rheology, including a yield stress and the phenomenon of shear banding.

Purpose of the Study:

• To review experimental data on shear banding in soft glassy materials.
• To present theoretical progress in understanding yield stress fluids and shear banding.
• To compare different theoretical approaches and identify remaining challenges.

Main Methods:

• Survey of experimental data on shear banding.
• Theoretical modeling using the soft glassy rheology (SGR) model and a simple fluidity model.
• Comparison with other theoretical frameworks like elasto-plastic models and shear transformation zone theories.

Main Results:

• Identification of two classes of yield stress fluids: those with permanent shear bands and those with transient bands.
• Theoretical models provide insights into the mechanisms behind shear banding.
• Transient shear bands can persist long enough to be mistaken for steady-state behavior.

Conclusions:

• Soft glassy rheology and fluidity models offer valuable frameworks for understanding yield stress fluids and shear banding.
• Further theoretical and experimental work is needed to fully address the complexities of these phenomena.
• Distinguishing between transient and permanent shear bands is crucial for accurate material characterization.