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

Abstract

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.

Lattice symmetries and the topologically protected transport of colloidal particles

“…The simplicity of C r 2 allows us to visualize many concepts that cannot be visualized for N > 2 such as the full dynamics in phase space. We also study the non-universal transport for N = 2, and the connection to previous works [32][33][34][35]. We outline the concept of topologically protected ratchets with this very simple example.…”

Taming polar active matter with moving substrates: directed transport and counterpropagating macrobands

“…Such a potential has previously been considered for active point particles [42] and disks [50] and can be realized e.g. by a micropatterned ferrite garnet film substrate [51], by optical lattices traversing at speeds of a few μ/s, or effectively (see figure 1(c)), simply by a tilted washboard potential [52][53][54]. Note here that in the comoving frame (moving with a constant velocity v L ) the dynamics translates into motion of a particle in a static tilted washboard potential (see figures 1(b), (c) and section 4).…”

“…Such a potential has previously been considered for active point particles [42] and disks [50] and can be realized e.g. by a micropatterned ferrite garnet film substrate [51], by optical lattices traversing at speeds of a few µ/s, or effectively (see Fig. 1 (c)), simply by a tilted washboard potential [52][53][54].…”

Bidirectional particle transport and size selective sorting of Brownian particles in a flashing spatially periodic energy landscape

“…Thus, for the discontinuous magnetic modulation used here, the magnetic dipolar interactions between particles of different sizes are irrelevant, as recently observed for a binary mixture of particles driven unidirectionally by a continuous modulation. 25 In contrast, the pair interactions between similar particles are non-negligible, as discussed in a previous work. 26 However, for the measurements of average speed, we avoid chain formation by using low concentrations of particles, such that the pair interactions do not affect the particle motion.…”