On aggregate structures in a rod-like haematite particle suspension by means of Brownian dynamics simulations

Abstract

We have investigated aggregation phenomena in a suspension composed of rod-like haematite particles by means of Brownian dynamics simulations. The magnetic moment of the haematite particles lies normal to the particle axis direction and therefore the present Brownian dynamics method takes into account the spin rotational Brownian motion about the particle axis. We have investigated the influence of the magnetic particle–field and particle–particle interactions, the shear rate and the volumetric fraction of particles on the particle aggregation phenomena. Snapshots of aggregate structures are used for a qualitative discussion and the cluster size distribution, radial distribution function and the orientational correlation functions of the direction of particle axis and magnetic moment are the focus for a quantitative discussion. The significant formation of raft-like clusters is found to occur at a magnetic particle–particle interaction strength much larger than that required for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters in a suspension of rod-like particles with a large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structure of the clusters, but influences the cluster size distribution of the raft-like clusters.

Keywords:

• magnetic colloidal dispersion
• Brownian dynamics method
• rod-like haematite particle
• simple shear flow
• aggregation phenomenon
• orientational correlation function

Additional information

Funding

The present study was partially supported by the Grant-in-Aid for Scientific Research of The Ministry of Education, Culture, Sports, Science and Technology of Japan [grant number 23360049].