Rheology dynamics of aggregating colloidal suspensions

Area of Science:

• Complex fluid rheology
• Colloidal science
• Population balance modeling

Background:

• Understanding the relationship between particle microstructure and macroscopic flow behavior in complex fluids is crucial.
• Two primary mechanisms governing particle collisions in suspensions are orthokinetic (shear-induced) and perikinetic (Brownian motion-induced).
• These distinct kinetics are hypothesized to influence the observed rheological properties, such as flow curves.

Purpose of the Study:

• To develop and analyze a colloidal model incorporating population balances to bridge microstructural kinetics and macroscale rheology.
• To investigate how orthokinetic and perikinetic particle collision mechanisms affect the flow behavior and steady-state shear profiles of colloidal suspensions.
• To determine the conditions under which shear banding occurs in these systems.

Main Methods:

• Developed a colloidal model based on population balances.
• Integrated the colloidal model with the 1D Stokes equation for laminar, incompressible Couette flow.
• Analyzed the resulting flow behaviors, focusing on monotonic vs. non-monotonic flow curves and steady-state shear profiles.

Main Results:

• Orthokinetic collisions result in monotonic flow curves and uniquely defined, continuous steady-state shear profiles.
• The presence of perikinetic collisions leads to non-monotonic flow curves and can result in shear banding and non-unique steady states.
• Shear banded configurations are dependent on initial conditions and collision kinetics; all cases exhibit continuous shear profiles at high shear rates.

Conclusions:

• The type of particle collision kinetics (orthokinetic vs. perikinetic) fundamentally dictates the rheological response and steady-state flow profiles of colloidal suspensions.
• The developed model successfully connects microstructural dynamics to macroscale rheological phenomena like shear banding.
• Initial conditions and collision mechanisms are critical factors in determining the occurrence and nature of shear banding in complex fluids.