Magnetophoresis of Weakly Magnetic Nanoparticle Suspension Around a Sphere

This study investigates the magnetophoresis behavior of weakly magnetic nanoparticle suspensions using spheres in a non-uniform magnetic field. Experiments and simulations were conducted to investigate the transport of particles over a broad range of conditions: concentration 10 ⩽ c ⩽ 100 mg/L, magnetic field of 0 - 1 T, and sphere diameter 0.2 - 5 mm. Moreover, to investigate the effect of magnetic susceptibility, a range of paramagnetic and diamagnetic nanoparticles were used in the experiments. The experimental setup consists of a standard cuvette and a sphere, placed between the two poles of an electromagnet. Experiments show that the paramagnetic nanoparticles were attracted toward the spheres, forming small vortices and concentrating near the surface, where the magnetic field gradient was high. Additionally, enhanced magnetic convection around the sphere drives the magnetophoresis phenomenon, strengthening it with increasing particle concentration and magnetic field. In contrast, the diamagnetic nanoparticles experience a repulsive force from regions of high magnetic field gradients, causing their movement away from the sphere. Due to gravitational forces, the diamagnetic particles move downwards and settle at the bottom of the cuvette. Furthermore, increasing the sphere diameter improved separation efficiency by promoting stronger particle enrichment around the sphere. This enhancement is due to the stronger magnetic field gradients generated by the increased surface area of the sphere.