Controlling the clustering behavior of particulate colloidal systems using alternating and rotating magnetic fields

摘要

Abstract Particle aggregates are often formed in particulate colloids. Different biological and industrial applications have specific preferences of particle cluster sizes. In this study, a computational model is developed to evaluate two novel strategies in controlling the aggregation behavior of magnetic-responsive particles using rotating and alternating magnetic fields. Computational fluid dynamics approach is adopted to model the base fluid, and a comprehensive soft sphere model is used to simulate the particle behaviors, with two-way coupling between the two phases. Under a static magnetic field with constant magnitude and direction, it is observed that magnetic-responsive particles form chain-like structures parallel to the direction of the magnetic field with an average longest dimension of about 8 µm when steady state is reached. When an external magnetic field with constant magnitude in a clockwise rotating direction is applied, particle aggregation is encouraged, and the chain-like structures formed are longer than in the static magnetic field case. When the direction of a constant-magnitude magnetic field alternates between two perpendicular directions, complete particle disaggregation is observed periodically. Three different frequencies are tested for the rotational and alternating magnetic field cases. It is observed that low-frequency rotating magnetic field is the most effective in encouraging particle aggregation with an average longest dimension of about 13 µm under steady-state, and high frequency alternating magnetic field is the most effective in disaggregating magnetic-responsive particle clusters, where the average longest dimension fluctuates between 3 and 5 µm under steady-state.Graphic abstract