Orthokinetic Aggregation in Two Dimensions of Monodisperse and Bidisperse Colloidal Systems

Area of Science:

• Colloid science
• Interface phenomena
• Rheology

Background:

• Orthokinetic aggregation is crucial for understanding colloidal systems.
• Direct imaging offers insights into dynamic processes at interfaces.
• Shear forces significantly influence particle interactions and cluster formation.

Purpose of the Study:

• To investigate orthokinetic aggregation of colloids at the air-liquid interface.
• To analyze cluster structure and mass distribution under shear.
• To understand how particle interactions affect aggregation kinetics.

Main Methods:

• Utilized direct imaging within a couette cell for real-time observation.
• Controlled interparticle interactions by adjusting electrolyte concentration.
• Created bidisperse systems by adding smaller particles to monodisperse suspensions.

Main Results:

• Observed high fractal dimensions in clusters, indicating shear-induced densification.
• Monodisperse systems showed homogeneous aggregation (large clusters joining large clusters).
• Bidisperse systems exhibited heterogeneous aggregation (small and large clusters interacting), with a slightly lower fractal dimension.

Conclusions:

• Shear rearrangement and densification are key factors in colloidal cluster formation.
• Aggregation mechanisms differ significantly between monodisperse and bidisperse colloidal systems.
• Fractal dimension serves as a metric for shear-induced structural changes in colloidal aggregates.