The Magnus effect is caused by the force perpendicular to the rotating axis of an object and its linear motion. Most applications of the Magnus force to date have focused on macroscopic objects, such as planet formation and spin on tennis balls.
Solsans et al. explored the effect in the microscopic realm. By keeping track of the anisotropic magnetic Janus particles as small as 80 μm through fluids with varying viscosity in the presence of a magnetic field rotating at different speeds, the authors were able to deduce the Magnus force from the trajectory deflections.
With Reynolds number close to 1, they found trajectory deflections of the order of 1 degree. Above a threshold field, the particles were subject to a Magnus force that caused a measurable tilt of up to 1.2 degrees in their trajectories.
The experimental approach allows them to rotate particles in a controlled manner and measure their trajectories at the same time. The method shows promise for sorting microparticles or objects loaded with magnetic particles by the distribution of magnetic moment and particle diameter.
“The major challenge was to convince ourselves that this phenomenon was measurable,” said author Miguel Solsona. “The topic of forces on microparticles has been extensively studied during the last 20 years, but nobody had published a study on the Magnus force on microparticles.”
The group next looks to use their work to sort particles or cells for a useful purpose such as sorting cancer cells or catalyst particles.
Source: “Trajectory deflection of spinning magnetic microparticles: The Magnus effect at the microscale,” by M. Solsona, H. Keizer, H. L. de Boer, Y. P. Klein, W. Olthuis, L. Abelmann, and A. van den Berg, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/1.5145064.
