Shear Thinning of Noncolloidal Suspensions

Area of Science:

• Rheology
• Soft Matter Physics
• Fluid Dynamics

Background:

• Shear thinning, a viscosity decrease with shear rate, is understood in colloidal systems via entropic forces.
• This phenomenon is observed in noncolloidal systems at high volume fractions, but its origin remains theoretically unexplained.
• Numerical simulations typically show shear thickening, contrasting experimental observations of shear thinning in noncolloidal suspensions.

Purpose of the Study:

• To propose a theoretical model explaining shear thinning in noncolloidal suspensions.
• To investigate the role of interparticle lubrication forces in suspension rheology.
• To reconcile simulation discrepancies with experimental observations of shear thinning.

Main Methods:

• Development of a non-Newtonian model for interparticle lubrication forces.
• Analysis of fluid behavior within narrow interparticle gaps at high volume fractions.
• Theoretical investigation of how suspending medium rheology influences overall suspension behavior.

Main Results:

• The proposed model successfully explains shear thinning in noncolloidal suspensions.
• Hidden shear-thinning effects in the suspending medium, active at high shear rates, induce overall suspension shear thinning at lower rates.
• High local shear rates in particle gaps amplify the impact of the fluid's non-Newtonian properties.

Conclusions:

• The rheology of the matrix fluid must be considered across a wide range of shear rates to understand noncolloidal suspension behavior.
• The model provides a theoretical basis for shear thinning in noncolloidal systems, addressing a gap in current understanding.
• This work highlights the importance of local fluid dynamics in determining macroscopic suspension properties.