Transport and selective chaining of bidisperse particles in a travelling wave potential

TL;DR

This study combines experiments, theory, and simulations to explore how a traveling magnetic landscape can selectively transport and chain different sizes of paramagnetic colloidal particles, enabling controlled particle assembly and confinement.

Contribution

It introduces a method to control and induce selective chaining of bidisperse particles using a traveling magnetic potential, with tunable interactions via magnetic field ellipticity.

Findings

Selective chaining of one particle type achieved

Particles of different sizes exhibit distinct mobilities

Chains confine non-chaining particles within channels

Abstract

We combine experiments, theory and numerical simulation to investigate the dynamics of a binary suspension of paramagnetic colloidal particles dispersed in water and transported above a stripe patterned magnetic garnet film. The substrate generates a one-dimensional periodic energy landscape above its surface. The application of an elliptically polarized rotating magnetic field causes the landscape to translate, inducing direct transport of paramagnetic particles placed above the film. The ellipticity of the applied field can be used to control and tune the interparticle interactions, from net repulsive to net attractive. When considering particles of two distinct sizes, we find that, depending on their elevation above the surface of the magnetic substrate, the particles feel effectively different potentials, resulting in different mobilities. We exploit this feature to induce selective chaining for certain values of the applied field parameters. In particular, when driving two types of particles, we force only one type to condense into travelling parallel chains. These chains confine the movement of the other non-chaining particles within narrow colloidal channels. This phenomenon is explained by considering the balance of pairwise magnetic forces between the particles and their individual coupling with the travelling landscape.