Colloid flow during thickening--a particle level understanding for core-shell particles

Area of Science:

• Colloid Science
• Rheology
• Computational Physics

Background:

• Concentrated colloidal suspensions exhibit shear thickening, a phenomenon with complex underlying mechanisms.
• Previous research identified a contact network between polymer coats as key to shear thickening.
• A mean-field argument links particle interactions to thickening, but an unknown factor related to contact destruction remains.

Purpose of the Study:

• To further understand the particle-level mechanisms of shear thickening in concentrated colloids.
• To investigate the structure and coordination of the particle contact network.
• To analyze the lifetimes of particle contacts and their role in the shear thickening regime.

Main Methods:

• Simulations using Stokesian dynamics for high concentrations.
• Analysis of the fabric and texture of the particle contact network.
• Examination of particle contact lifetimes and stress fluctuations.

Main Results:

• The study contrasts systems with varying polymer coat thicknesses.
• Tentative evidence suggests the network structure approaches isostatic coordination.
• Analysis of contact lifetimes reveals some pairs have surprisingly long durations.
• Data on stress fluctuations in the thickening regime is presented.

Conclusions:

• The formation and coordination of particle contact networks are crucial for shear thickening.
• The lifetimes of particle contacts play a significant role, challenging simple pair arguments.
• Further investigation into contact dynamics and network evolution is warranted for a complete understanding.