Kinetics of Low Field Gradient Magnetophoresis in the Presence of Magnetically Induced Convection

© 2017 American Chemical Society. Previous work (Leong et al. Soft Matter 2015, 11, 6968) has demonstrated, by using both experiments and simulations, that a magnetic field gradient can induce substantial convective currents during magnetophoresis of superparamagnetic nanoparticles in the solution. This effect substantially enhances the efficiency of low gradient magnetic separation (LGMS) processes. Throughout the LGMS process, this circulating flow plays a dominant role in homogenizing the nanoparticle solution and enhancing the vertical motion of particles. Here we perform a detailed quantitative study of the factors affecting the kinetics of LGMS in the presence of magnetically induced convection. In particular, we have found that the magnetophoretic collection rate of magnetic nanoparticles in LGMS is solely determined by the magnetic field gradient at the surface of contact of the dispersion cuvette with the magnet (denoted as the "collection plane of particles" in this work) and the area of this surface. Surprisingly, the kinetics of LGMS is independent of the magnetic field distribution across the solution subjected to magnetophoresis as long as magnetically induced convection is present. These conclusions are of crucial relevance in the design of low gradient magnetic separators for engineering applications. (Figure Presented).