(431f) Monte-Carlo and Brownian Dynamic Simulaitons of Self-Assembly and Gelation of Magnetic Particles IN the PRESENCE of A Magnetic Field

The behavior of dispersions of magnetic particles in the presence and in the absence of a magnetic field has been the subject of numerous experimental studies and theoretical investigations. The goal of these studies was to elucidate the effect of dipolar interactions on the spontaneous formation of clusters and their orientation in the presence of a magnetic field, as well as the existence of such clusters in the absence of a field. However, only a few experimental studies have tried to focus on the behavior of concentrated suspensions of magnetic particles, while the simulation works have only covered the behavior of relatively diluted suspensions. In addition, so far all of these studies have been carried out in the case of colloidally stable magnetic particles.

On the other hand, the self-assembly of destabilized non-magnetic colloidal particles is a very well understood phenomenon, leading to the formation of well know fractal clusters with a fractal dimension ranging between 1.8 and 2.1 depending upon the absence or presence of repulsive interactions, respectively. It is also well know that colloidal dispersions can undergo gelation when fractal clusters reach sufficient size to percolate into an infinite network.

With the purpose of bridging this existing gap, and of utilizing magnetic particles for the preparation of novel porous materials with controlled properties, we set out to understand the self-assembly behavior of either completely or partially destabilized superparamagnetic colloidal particles in the presence of a magnetic field. We have carried out Monte-Carlo simulations to investigate the structure and morphology of clusters and gels made of superparamagnetic colloids in the presence of magnetic field, as a function of particle size and magnitude of repulsive interactions. All the inter-particles interactions, i.e., dipolar, Van der Waals, and electrostatic are rigorously accounted for. Our primary objective is to analyze the anisotropy in the structure of gels obtained with magnetic fields applied at different stages during the gelation process. Additionally, we have also carried out Brownian dynamic simulations on the same system to better understand the effect of magnetic fields on the kinetics of clusters and gel formation. Comparison with experimental data from our lab is performed.