Aggregation in Colloidal Suspensions: Evaluation of the Role of Hydrodynamic Interactions by Means of Numerical Simulations

Numerical simulations constitute
a precious tool for understanding
the role of key parameters influencing the colloidal arrangement in
suspensions, which is crucial for many applications. The present paper
investigates numerically the role of hydrodynamic interactions on
the aggregation processes in colloidal suspensions. Three simulation
techniques are used: Brownian dynamics without hydrodynamic interactions,
Brownian dynamics including some of the hydrodynamic interactions,
using the Yamakawa–Rotne–Prager tensor, and stochastic
rotation dynamics coupled with molecular dynamics. A system of monodisperse
colloids strongly interacting through a generalized Lennard-Jones
potential is studied for a colloid volume fraction ranging from 2.5
to 20%. Interestingly, effects of the hydrodynamic interactions are
shown in the details of the aggregation processes. It is observed
that the hydrodynamic interactions slow down the aggregation kinetics
in the initial nucleation stage, while they speed up the next cluster
coalescence stage. It is shown that the latter is due to an enhanced
cluster diffusion in the simulations including hydrodynamic interactions.
The higher the colloid volume fraction, the more pronounced the effects
on the aggregation kinetics. It is also observed that hydrodynamic
interactions slow down the reorganization kinetics. It turns out that
the Brownian dynamics technique using the Yamakawa–Rotne–Prager
tensor tends to overestimate the effects on cluster diffusion and
cluster reorganization, even if it can be a method of choice for very
dilute suspensions.