(113b) Analysis of the Dynamics and Interactions of Magnetic Nanoparticles in Gradient and Time-Varying Magnetic Fields

The interest in magnetic nanoparticles and ferrofluids has grown substantially in recent years as their applications continue to proliferate. Current applications are diverse and include the transport of biomolecules and therapeutic drugs, gene transfection, bioseparation, ferrofluidic seals and pumps, microfluidic mixers and magnetoresistive-based sensors, among others. However, despite the widespread and growing use of magnetic nanoparticles, there are many fundamental aspects of their collective behavior that remain unknown. Of particular interest is the self-assembly of the particles in a gradient field and the response of assembled particle-based microstructures in a time-varying field. In this presentation, a model is presented for predicting the field-directed assembly of colloidal magnetic particles under the influence of a high-gradient magnetic field and the manipulation of extended magnetic structures in a time varying field. The model is based on a modified discrete element method and takes into account several competitive effects. These include the applied magnetics force, induced magnetic dipole-dipole interactions, Brownian dynamics, Van der Waals interaction, a repulse contact force, viscous damping and hydrodynamic interactions among the particles. A dynamic time-stepping approach is used in the model to stabilize and accelerate the computation. The model is useful for predicting the structure of assembled particles in a given field and the stability of such structures in a time varying field. The model is demonstrated via application to various nanoparticle systems.