Multiple yielding processes in a colloidal gel under large amplitude oscillatory stress

Area of Science:

• Soft matter physics
• Materials science
• Rheology

Background:

• Material fatigue is well-studied in construction materials but less understood in soft materials.
• Colloidal gels exhibit complex behaviors under mechanical stress.

Purpose of the Study:

• To characterize the fatigue dynamics of colloidal gels under large amplitude oscillatory stress.
• To identify the stages of fatigue leading to gel rupture and fluidization.
• To explore the relationship between fatigue dynamics and stress oscillation parameters.

Main Methods:

• Inducing fatigue using large amplitude oscillatory stress (LAOStress).
• Measuring local gel displacements with high-frequency ultrasonic imaging.
• Analyzing the scaling of fatigue step durations with stress oscillation amplitude (σ0).

Main Results:

• Fatigue progresses through four distinct stages: solid, wall sliding, heterogeneous solid-fluid coexistence, and full fluidization.
• The duration of each fatigue stage scales homogeneously with stress oscillation amplitude (σ0).
• Scaling data support both exponential and power-law models, hinting at activated processes or Basquin law.
• Model parameters show non-monotonic behavior with changes in oscillation frequency and/or gel concentration.

Conclusions:

• Colloidal gel fatigue leads to eventual rupture and fluidization through a predictable sequence of stages.
• The stress oscillation amplitude is a key factor in controlling fatigue dynamics and delayed yielding.
• Non-monotonic parameter behavior suggests complex underlying mechanisms in soft material fatigue.