Rheological State Diagrams for Rough Colloids in Shear Flow

Area of Science:

• Colloid and Surface Science
• Rheology
• Materials Science

Background:

• Colloidal suspensions exhibit complex rheological behaviors, including shear thickening and dilatancy.
• The role of particle surface properties, such as roughness, in dictating these behaviors is not fully understood.

Purpose of the Study:

• To investigate the influence of particle surface roughness on the rheological properties of concentrated colloidal suspensions.
• To elucidate the mechanisms by which surface roughness affects shear thickening, dilatancy, and normal stress responses.

Main Methods:

• Development of model colloids with controlled surface roughness length scales.
• Rheological measurements including shear stress, volume fraction, and normal stress analysis.
• Computer simulations of colloidal suspensions with adjustable friction coefficients.

Main Results:

• Increased particle roughness shifts the onset of shear thickening and dilatancy to lower volume fractions and critical stresses.
• Surface roughness enhances the effective packing fraction in the quasi-Newtonian flow regime.
• A sign change in the first normal stresses and reduced critical contact forces were observed with increasing roughness, indicating a transition to roughness-induced interactions.

Conclusions:

• Particle roughness is a critical factor governing the rheology of concentrated colloidal suspensions.
• Surface roughness modifies interparticle forces, leading to altered jamming transitions and load-bearing contact mechanisms.
• Findings provide insights into designing and predicting the flow behavior of particulate materials.