Dynamics of magnetic nanoparticle suspensions

TL;DR

This paper investigates how polydispersity, interactions, and thermal effects influence the dynamics and clustering behavior of magnetic nanoparticle suspensions, providing models and methods to analyze their size distribution and response functions.

Contribution

It introduces a comprehensive model for nanoparticle dynamics considering polydispersity, interactions, and fragmentation, along with a procedure to extract size distributions from experimental data.

Findings

Polydispersity significantly alters response functions.

Aggregation and fragmentation processes determine cluster size distributions.

The proposed models match experimental observations satisfactorily.

Abstract

We study the dynamics of a suspension of magnetic nanoparticles. Their relaxation times are strongly size-dependent. The dominant mode of relaxation is also governed by the size of the particles. As a result the dynamics is greatly altered due to polydispersity in the sample. We study the effect of polydispersity on the response functions. These exhibit significant changes as the parameters characterizing polydispersity are varied. We also provide a procedure to extract the particle size distribution in a polydisperse sample using Cole-Cole plots. Further the presence of attractive interactions causes aggregation of particles leading to the formation of clusters. Repulsive interactions along with thermal disorder not only hinder aggregation, but also introduce the possibility of removal of particles or "fragmentation" from clusters. The competing mechanisms of aggregation and fragmentation yield a distribution of cluster sizes in the steady-state. We attempt to understand the formation of clusters and their distributions using a model incorporating the phenomena of aggregation and fragmentation. Scaling forms for quantities of interest have been obtained. Finally we compare our numerical results with experimental data. These comparisons are satisfactory.