Magnetophoretic Sprinting: A Study on the Magnetic Properties of Aqueous Lanthanide Solutions

Abstract

Droplets of aqueous solutions of trivalent lanthanide ions (Ln 3+) were formed inside an immiscible fluid. The motion of the droplets, induced by the magnetic field of a Nd−Fe−B permanent magnet, was measured. By using the relationship between the magnetophoretic velocity, the magnetic force, and the frictional coefficient, a good estimate of the magnetic susceptibility was obtained. The impact of the magnetic susceptibility of each Ln 3+ ion on the magnetophoresis was analyzed. Additionally, the influence of droplet volume, concentration. and magnetic field strength was also studied. A forward motion toward regions of stronger magnetic field was observed for droplets of paramagnetic solutions, while no motion was detected for droplets of diamagnetic solutions. The average droplet velocity for the different Ln 3+ ions across the lanthanide series follows a binodal-shaped curve, which corresponds to the change of the magnetic susceptibility of Ln 3+ as a function of the atomic number. Strongly paramagnetic ions develop a considerably higher velocity compared to weakly paramagnetic ions, in a process which we denote here as "magnetophoretic sprinting".

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