Rheological hysteresis in soft glassy materials

Area of Science:

• Soft Matter Physics
• Rheology
• Materials Science

Background:

• Nonlinear rheology describes complex fluid behavior using shear stress vs. shear rate.
• Rheological hysteresis loops occur when up and down shear rate sweeps do not superimpose.
• Understanding hysteresis is key to characterizing soft glassy materials.

Purpose of the Study:

• To investigate the local mechanisms behind rheological hysteresis in soft glassy materials.
• To introduce quantitative observables for macroscopic and local hysteresis.
• To establish a universal framework for soft glassy material rheology.

Main Methods:

• Extensive rheometry measurements.
• Time-resolved velocimetry to probe local flow dynamics.
• Analysis of macroscopic and local observables as a function of sweep rate.

Main Results:

• Two observables quantify macroscopic and local hysteresis, both showing a maximum with sweep rate.
• A material-dependent time scale emerges from the sweep rate dependence.
• This time scale ranges from small values in yield stress fluids to large values in time-dependent materials.

Conclusions:

• Experimental results support a universal time scale-based framework for soft glassy materials.
• Inhomogeneous flows, such as shear banding and plug flow, are central to rheological hysteresis.
• The findings provide insights into the fundamental rheological properties of complex fluids.