Magnetophoresis of paramagnetic and diamagnetic nanoparticle suspensions under magnetic field gradients

In this talk, I will discuss our recent efforts in understanding the dynamics of weakly magnetic nanoparticle suspensions in non-uniform magnetic fields. I will present the results for two scenarios, where magnetic field gradients are produced using either a conical pole of an electromagnet and/or by introducing a magnetized wire. The experiments are conducted within a closed rectangular cuvette, with a wire positioned between the poles of an electromagnet. Two types of nanoparticles—paramagnetic manganese oxide and diamagnetic bismuth oxide—are studied across a broad range of concentrations (10–100 mg/L), magnetic field strengths (0.25–1 T), and wire diameters (0.8–3 mm). The experimental results reveal that paramagnetic manganese oxide nanoparticles exhibit significant magnetophoretic behavior, leading to particle depletion within the cuvette. The depletion rate is independent of the initial particle concentration but strongly depends on the magnetic field gradient. In contrast, diamagnetic nanoparticles exhibit markedly different behavior, with their magnetophoresis dynamics showing minimal dependence on magnetic field strength, while being inversely proportional to the wire diameter. Transient concentration gradients emerge within the cuvette, which we hypothesize are driven by magnetic Grashof number. Multiphysics numerical simulations reveal formation of field-induced particle clusters in weakly paramagnetic nanoparticles, which enhance magnetophoresis.