Numerical investigation of magnetic-field induced self-assembly of nonmagnetic particles in magnetic fluids

The underlying mechanisms of controlling the self-assembly of micro-size nonmagnetic particles (NPs) in magnetic fluids are essential for the manufacture, process and exploitation of nano-magnetic material. In this study, a multi-physical numerical model, which couples a distribution function correction-based immersed boundary lattice Boltzmann method (DFCIB-LBM) for fluid–structure interaction (FSI) and a self-correcting procedure of Poisson equation solver for magnetic field, is carried out to investigate such self-assembling behaviors and mechanisms. The interactions of two neighboring micro-size NPs placed in different distance and orientation, and the self-assembling behaviors of numerous micro-size NPs under uniform magnetic field are studied in details. The results demonstrate that the self-assembling behaviors are caused by the inverse magnetic effect, which can be adjusted by varying the concentration and size of NPs, permeability ratio, and the strength of external magnetic field. On the contrary, NPs in magnetic fluid affect their surrounding magnetic field and hinder the magnetization near the NP boundary region. These findings can provide a better understanding of the bottom-up fabrication of magnetic functional materials and devices.