Fission and fusion scenarios for magnetic microswimmer clusters

Abstract

Fission and fusion processes of particle clusters occur in many areas of physics and chemistry from subnuclear to astronomic length scales. Here we study fission and fusion of magnetic microswimmer clusters as governed by their hydrodynamic and dipolar interactions. Rich scenarios are found that depend crucially on whether the swimmer is a pusher or a puller. In particular a linear magnetic chain of pullers is stable while a pusher chain shows a cascade of fission (or disassembly) processes as the self-propulsion velocity is increased. Contrarily, magnetic ring clusters show fission for any type of swimmer. Moreover, we find a plethora of possible fusion (or assembly) scenarios if a single swimmer collides with a ringlike cluster and two rings spontaneously collide. Our predictions are obtained by computer simulations and verifiable in experiments on active colloidal Janus particles and magnetotactic bacteria.

Dynamical self-assembly of dipolar active Brownian particles in two dimensions

“…For example, ref. 13 and 14 have studied the structural transformation of small dipolar clusters under the impact of activity starting from different (meta)stable configurations, either neglecting 13 or including 14 hydrodynamic interactions. Another example is a system of spherical, ferromagnetic rollers confined to a fluctuating surface.…”

Magnetotactic bacteria in a droplet self-assemble into a rotary motor

“…For example, the magnetic alignment, combined with a micro-aerotactic swimming response, qualifies such micro-swimmers as a promising vector for targeted drug therapy [32]. Recently, it was proposed, on theoretical grounds, that a suspension of such magnetotactic bacteria could display original magneto-rheological properties [33,34], novel pattern formation [35] and hydrodynamic instabilities [36,37].…”

Gravity-induced dynamics of a squirmer microswimmer in wall proximity

“…biological organisms [11,12] and synthetic particles [13,14] as well as continuum models thereof [15]. A decisive factor for such microswimmers are hydrodynamic interactions with surfaces and with each other [16][17][18][19][20][21][22][23][24][25][26][27].…”