Transport and diffusion of paramagnetic ellipsoidal particles in a rotating magnetic field

TL;DR

This study numerically investigates how paramagnetic ellipsoidal particles move and diffuse in a rotating magnetic field within a channel, revealing mechanisms for particle separation, orientation control, and diffusion enhancement.

Contribution

It introduces a detailed numerical analysis of active and passive paramagnetic ellipsoidal particles under rotating magnetic fields, highlighting parameter optimization for particle manipulation.

Findings

Active particles exhibit more complex transport behaviors than passive ones.

Rotational motion affects diffusion and rectification differently depending on synchronization with the magnetic field.

Particles can be separated based on shape, speed, or diffusion rate by tuning magnetic field parameters.

Abstract

Transport and diffusion of paramagnetic ellipsoidal particles under the action of a rotating magnetic field are numerically investigated in a two-dimensional channel. It is found that paramagnetic ellipsoidal particles in a rotating magnetic field can be rectified in the upper-lower asymmetric channel. The transport and the effective diffusion coefficient are much more different and complicated for active particles, while they have similar behaviors and change a little when applying rotating magnetic fields of different frequencies for passive particles. For active particles, the back-and-forth rotational motion facilitates the effective diffusion coefficient and reduces the rectification, whereas the rotational motion synchronous with the magnetic field suppresses the effective diffusion coefficient and enhances the rectification. There exist optimized values of the parameters (the anisotropic degree, the amplitude and frequency of magnetic field, the self-propelled velocity, and the rotational diffusion rate) at which the average velocity and diffusion take their maximal values. Particles with different shapes, self-propelled speeds, or rotational diffusion rates will move to the opposite directions and can be separated by applying rotating magnetic fields of suitable strength and frequency. Our results can be used to separate particles, orient the particles along any direction at will during motion, and control the particle diffusion.