Three-dimensional imaging of colloidal glasses under steady shear

Area of Science:

• Colloid and interface science
• Soft matter physics
• Rheology

Background:

• Understanding particle dynamics in colloidal glasses under shear is crucial for material science.
• Existing models often simplify the complex behavior of these systems.

Purpose of the Study:

• To investigate the three-dimensional particle dynamics in a yielded hard-sphere colloidal glass under steady shear.
• To compare the structural relaxation and diffusion with quiescent colloidal fluids.
• To analyze the relationship between local shear rate and material properties.

Main Methods:

• Utilized fast confocal microscopy to image particle movement.
• Applied steady shear to a hard-sphere colloidal glass.
• Analyzed structural relaxation and diffusion constants.

Main Results:

• Observed nearly isotropic structural relaxation in uniform shear regions, differing from quiescent fluids.
• Found shear thinning behavior: inverse relaxation time and diffusion constant scale with local shear rate (gamma*^0.8).
• Noted a discrepancy between local dynamics and global rheology (Herschel-Bulkley behavior).

Conclusions:

• Local particle dynamics exhibit significant shear thinning, distinct from global rheological measurements.
• Shear localization may explain the differences between local and global behaviors.
• The findings provide insights into the complex flow of soft glassy materials.