Age-dependent transient shear banding in soft glasses

Area of Science:

• Soft matter physics
• Rheology
• Materials science

Background:

• Soft glasses exhibit complex flow behaviors under shear.
• Understanding transient phenomena is crucial for predicting material response.

Purpose of the Study:

• To numerically investigate the formation and duration of transient shear bands in soft glasses.
• To analyze the influence of shear rate and sample age on banding.
• To determine the origin of the banding instability.

Main Methods:

• Numerical simulations of two soft glass models: a simple fluidity model and a soft glassy rheology (SGR) model.
• Analysis of shear startup flow dynamics.
• Examination of the relationship between banding and stress overshoot.

Main Results:

• Long-lived transient shear bands form during shear startup in both models.
• Banding degree and duration depend significantly on applied shear rate and sample age.
• The steady flow state remains homogeneous, despite transient banding.
• Banding instability is associated with stress overshoot, not purely viscous or elastic effects.

Conclusions:

• Soft glasses can display long-lived transient shear banding under startup shear.
• The observed banding is a transient phenomenon preceding a homogeneous steady state.
• Stress overshoot is a key indicator and potential driver of shear banding instability in these systems.