Diffusion limited cluster aggregation with irreversible flexible bonds

TL;DR

This study simulates irreversible diffusion limited cluster aggregation of hard spheres with flexible bonds, revealing effects on structure, densification, aging, and heterogeneity in gels, with implications for understanding gelation processes.

Contribution

It introduces a simulation of DLCA with flexible bonds, showing how bond flexibility influences cluster densification, structure, and aging without bond breaking.

Findings

Bond flexibility causes local densification and order in clusters and gels.

Restructuring and aging occur over long times without bond breaking.

Heterogeneous particle mobility increases at lower volume fractions.

Abstract

Irreversible diffusion limited cluster aggregation (DLCA) of hard spheres was simulated using Brownian cluster dynamics. Bound spheres were allowed to move freely within a specified range, but no bond breaking was allowed. The structure and size distribution of the clusters was investigated before gelation. The pair correlation function and the static structure factor of the gels were determined as a function of the volume fraction and time. Bond flexibility led to local densification of the clusters and the gels, with a certain degree of order. At low volume fractions densification of the clusters occurred during their growth, but at higher volume fractions it occurred mainly after gelation. At very low volume fractions, the large scale structure (fractal dimension), size distribution and growth kinetics of the clusters was found to be close to that known for DLCA with rigid bonds. Restructuring of the gels continued for long times, indicating that aging processes in systems with strong attraction do not necessarily involve bond breaking. The mean square displacement of particles in the gels was determined. It is shown to be highly heterogeneous and to increase with decreasing volume fraction.