Rheology, microstructure and migration in brownian colloidal suspensions.

Area of Science:

• Computational physics and chemistry
• Soft matter physics
• Fluid dynamics

Background:

• Simulating colloidal suspensions requires accurate models for particle interactions and fluid behavior.
• Standard dissipative particle dynamics (DPD) has limitations in capturing complex suspension dynamics, particularly concerning angular momentum.

Purpose of the Study:

• To develop and validate an enhanced dissipative particle dynamics (DPD) formulation for modeling colloidal suspensions.
• To investigate the rheology, microstructure, and shear-induced migration of monodisperse colloidal suspensions in various flow conditions.

Main Methods:

• A novel DPD formulation incorporating noncentral dissipative shear forces and preserving angular momentum was developed.
• Exponential conservative forces were used for colloid-colloid and colloid-solvent interactions, while linear forces were used for solvent-solvent interactions.
• Simulations were performed for plane shear flows (Couette and Poiseuille) to analyze rheological properties and particle behavior.

Main Results:

• The enhanced DPD model accurately predicts relative viscosity, shear-dependent viscosity, and normal-stress differences, aligning with experimental data and empirical correlations.
• Simulations revealed flow-induced transitions to ordered (string-like) structures at low shear rates and disordered states at higher rates, consistent with experimental observations.
• The model successfully reproduced shear-induced migration effects in Poiseuille flow and highlighted the significance of angular momentum in non-dilute suspensions.

Conclusions:

• The proposed DPD formulation provides a robust and computationally efficient method for simulating complex fluid systems, particularly colloidal suspensions.
• The inclusion of angular momentum and noncentral forces significantly improves the model's ability to capture suspension behavior compared to standard DPD.
• This advanced DPD approach offers a promising alternative to methods like Stokesian Dynamics for studying non-dilute suspensions.