Structural crossover in dense irreversibly aggregating particulate systems

Abstract

Cluster-cluster aggregation has been simulated by off-lattice Monte Carlo methods for diffusion-limited (DLCA), ballistic-limited, and reaction-limited cluster aggregation classes. We find that as the system evolves and becomes dense, the largest cluster develops a hybrid structure with mass fractal dimension D(f) approximately 2.6 over large length scales, while at smaller length scales, the early time dilute-limit fractal structure is frozen in. The largest cluster is thus an aggregate of smaller aggregates with a different fractal dimension, and we call it a "superaggregate." The crossover length separating the two morphologies, which we call the critical radius of gyration, can be calculated based on a simple theory that assumes a monodisperse cluster size distribution. This agrees well with simulation results for DLCA. However, for other classes we find that the increasing polydispersity in cluster size pushes the simulated crossover length radius of gyration to values systematically larger than the predicted value.

The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

“…This proposition was based on simulation studies from this laboratory, which showed that DLCA can proceed creating = 1.8 fractal aggregates until the system becomes cluster dense [18]. Cluster dense is when the cluster mean nearest neighbor separation becomes comparable to the cluster size.…”

Aerosol Gelation: Synthesis of a Novel, Lightweight, High Specific Surface Area Material

“…Subsequently our laboratory has reported gelation of soot in laminar diffusion flames (Sorensen et al 1998;Kim et al 2006). Simulations (Gimel et al 1995(Gimel et al , 1999Hasmy and Jullien 1996;Fry et al 2004) imply that any system of particles undergoing aggregation can form a gel if the combining particles do not coalesce, and if the time to reach the gel point is shorter than other time scales that can deter gel formation. Non-coalescence is necessary so that the aggregating particles will form a non-dense (ramified) fractal aggregate with fractal dimension, D, less than the spatial dimension, d. When D < d, the average cluster separation to cluster size ratio falls with time during aggregation until the separation equals the size.…”

Coarse-Graining Approach to Infer Mesoscale Interaction Potentials from Atomistic Interactions for Aggregating Systems

“…In MD, the solute−solute, solute−solvent, and solvent−solvent interactions are described by a truncated Lennard-Jones (12-6) potential: (2) where σ is the particle diameter, r ij is the separation between centers of particles i and j, r cut is the cutoff distance chosen to be 2.5σ, and ε αβ is the potential well-depth between α and β particles (α,β = A,B). The dimensionless potential well depth is defined as (3) where T ref is the reference temperature chosen to be 121 K in these simulations. The reference temperature and particle size (σ = 3.4A) were chosen on the basis of the Lennard-Jones model for liquid argon.…”