Diffusion-limited cluster aggregation: Impact of rotational diffusion

TL;DR

This paper shows that rotational diffusion during diffusion-limited cluster aggregation significantly alters the structure of the resulting aggregates, challenging previous assumptions of a universal fractal dimension.

Contribution

It demonstrates that rotational diffusion affects aggregate structure, allowing tuning of fractal dimensions below the traditional limit in DLCA models.

Findings

Rotational diffusion lowers the fractal dimension of aggregates.

The fractal dimension decreases with increasing rotational to translational diffusion ratio.

Rotational movement can be used to control aggregate porosity.

Abstract

Diffusion-limited cluster aggregation (DLCA) is a well established model for the formation of highly porous low-density non-equilibrium structures. One of the main conclusions of the previous studies considering this model is that the rotational diffusion of aggregating clusters does not change their structure characterized by a universal fractal dimension of $d_f=1.7-1.8$. In contradiction to this assumption, we demonstrate that the rotation movement of clusters significantly changes the structure of forming aggregates. The fractal dimension of rotating clusters is lower than the one found in the standard DLCA model and decreases with the increasing ratio of rotational and translational diffusion constants $D_r/D_t$, which offers a possibility to tune the structures of the aggregates below the conventional DLCA fractal dimension limit.