Fractal properties of clusters of colloidal magnetic particles

TL;DR

This study investigates the fractal and structural properties of colloidal magnetic particle clusters formed via a 2D aggregation model, revealing temperature-dependent fractal dimensions and phase transitions from ordered to disordered states.

Contribution

It introduces a model analyzing how dipolar interactions influence cluster fractal dimensions and order-disorder transitions in colloidal magnetic particles.

Findings

Fractal dimension decreases with increasing temperature.

Ordered states exist at low temperatures and are destroyed at high temperatures.

Results relate to phase transitions in dipolar colloids and monolayers.

Abstract

We have studied the properties of clusters of colloidal magnetic particles generated from a 2D aggregation model with dipolar interparticle interactions. Particles diffuse off-lattice, experiencing dipolar interactions with the already attached particles until either they stick to the cluster or wander far away and are removed. Our results are interpreted in terms of a fractal dimension that is a monotonically decreasing function of the temperature, varying between a definite value close to 1 at T=0, and the limit $T\to\infty$, corresponding to free diffusion-limited aggregation. By analyzing orientational correlation functions, an ordered state is found at low temperatures; this state is destroyed by the fractal disorder generated at high $T$. Our study could be relevant in understanding aggregation of dipolar colloids and phase transitions in Langmuir monolayers.