Effect of particle size distribution on aggregate structures of cubic hematite particles in quasi-2D system (without applied magnetic field).

We considered a dispersion composed of polydisperse cubic hematite particles in thermodynamic equilibrium, and conducted cluster-moving Monte Carlo (MC) simulations to investigate the internal structure of cubic particle aggregates in a quasi-2D system. The investigation focused on various factors, such as the strength of magnetic particle–particle interaction, the standard deviation of the particle size distribution, and the volumetric fraction of particles. In a polydisperse system with a small standard deviation, cubic particles tended to aggregate and form closely packed structures with almost perfect face-to-face configuration, as in the case of a monodisperse system. In a polydisperse system with a larger standard deviation, only large particles tended to aggregate and form closely packed clusters with an aligned face-to-face configuration, while small particles moved as single particles in the system, because the magnitude of the magnetic moments is proportional to the particle volume. The magnetic interactions between small particles are not sufficiently strong for the particles to come into contact. Therefore, an increase in the standard deviation leads to unstable face-to-face contact within closely packed clusters. In a polydisperse system with a larger standard deviation, an increase in the volumetric fraction promotes aggregation, but smaller particles preserve their individual status. Highlights of the present paper: We developed a Monte Carlo simulation technique for suspension composed of polydisperse cubic hematite particles. We investigated dependence of aggregate structures of cubic particles on particle size distribution. In a polydisperse system with larger standard deviation, only large particles tend to aggregate to form closely packed clusters, while small particles remain as single particles. Increase in standard deviation leads to unstable face-to-face contact within closely packed clusters. [ABSTRACT FROM AUTHOR]