Cluster-cluster aggregation simulation in a concentrated suspension

Area of Science:

• Colloid and Surface Science
• Computational Physics
• Chemical Engineering

Background:

• The collision radius is crucial for understanding particle floc aggregation kinetics.
• Particle flocs exhibit wide size distributions, complicating aggregation modeling.
• Fractal aggregates are common in various natural and industrial processes.

Purpose of the Study:

• To characterize the collision radius of fractal aggregates formed via off-lattice diffusion-limited cluster-cluster aggregation (DLCCA).
• To investigate the relationship between collision radius, floc structure, and aggregation kinetics.
• To analyze the influence of initial volume fraction on fractal dimensions and aggregation rates.

Main Methods:

• Off-lattice diffusion-limited cluster-cluster aggregation (DLCCA) simulations were employed.
• The collision radius was estimated and correlated with the number of primary particles.
• Partial radial distribution functions were analyzed to understand particle spatial distribution.

Main Results:

• A fractal relationship was found between the collision radius and the number of primary particles.
• Floc fractal dimensions increased to ~2.5 at initial volume fractions above 8%, deviating from the typical 1.6-1.8 range.
• Aggregation rates increased with initial volume fraction, with deviations from standard population balance models at high concentrations due to a 'caging effect'.

Conclusions:

• The spatial distribution of particles significantly influences floc fractal dimensions and aggregation behavior.
• Standard population balance models require adjustments for transient collision flux, excluded volumes, and polydispersity.
• A 'caging effect' becomes dominant at high initial volume fractions, limiting aggregation rates and validating the DLCCA simulation findings.