Deformation profiles and microscopic dynamics of complex fluids during oscillatory shear experiments

Area of Science:

• Rheology and Complex Fluids
• Soft Matter Physics
• Materials Science

Background:

• Oscillatory shear tests are crucial for characterizing complex fluid mechanics.
• Understanding the relationship between macroscopic rheology and microscopic material behavior is essential.
• Detailed knowledge of the deformation field during shear tests is increasingly sought.

Purpose of the Study:

• To visualize and quantify the dynamics of tracers in cyclically sheared complex fluids.
• To investigate the yielding transition in yield stress fluids.
• To develop a tracking-free method for mapping sample rearrangements.

Main Methods:

• Utilizing a strain-controlled shear-cell with transparent walls for visualization.
• Employing image correlation processing to measure macroscopic deformation.
• Applying echo-differential dynamic microscopy to probe microscopic dynamics in reciprocal space.

Main Results:

• Characterization of wave-vector dependent shear-induced diffusion across the yielding transition.
• Observed a three-order-of-magnitude speed-up in dynamics during yielding.
• Transition from localized, intermittent rearrangements to homogeneous activity.

Conclusions:

• The developed tracking-free approach is intrinsically multi-scale and automatable.
• This method can discriminate between different dynamic behaviors in complex fluids.
• The technique is versatile and applicable to various imaging modes and tracer types.