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Fission and fusion scenarios for magnetic microswimmer clusters

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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.

No MeSH data available.


Alignment of dipoles within a ring-like structure.Alignment of the swimmer within a ring-like chain measured by the product of the swimmers orientation  and R=ri−rcv for (a) N=3, (b) N=4 and (c) N=5 swimmers.
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f6: Alignment of dipoles within a ring-like structure.Alignment of the swimmer within a ring-like chain measured by the product of the swimmers orientation and R=ri−rcv for (a) N=3, (b) N=4 and (c) N=5 swimmers.

Mentions: Let us start with a ring-like cluster of N=3 microswimmers. Figure 5a shows the flow field of a single microswimmer and indicates the position of the two other particles within the ring by grey dots. While these additional particles are attracted in case of pushers, the neighbouring particles are repelled in case of neutral swimmers and pullers. Hence the rings show the expected shrinking and swelling behaviours, see again Fig. 4a. The velocity dependence of the inverse radius of gyration for pushers is non-mononotic. This is a result of an induced torque on each particle, Fig. 6a, which leads to a ring configuration where the dipoles point outwards. This state is non-favorable for magnetic dipoles and, therefore, even pushers show a swelling behaviour for velocities v/v0>2.7.


Fission and fusion scenarios for magnetic microswimmer clusters
Alignment of dipoles within a ring-like structure.Alignment of the swimmer within a ring-like chain measured by the product of the swimmers orientation  and R=ri−rcv for (a) N=3, (b) N=4 and (c) N=5 swimmers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121419&req=5

f6: Alignment of dipoles within a ring-like structure.Alignment of the swimmer within a ring-like chain measured by the product of the swimmers orientation and R=ri−rcv for (a) N=3, (b) N=4 and (c) N=5 swimmers.
Mentions: Let us start with a ring-like cluster of N=3 microswimmers. Figure 5a shows the flow field of a single microswimmer and indicates the position of the two other particles within the ring by grey dots. While these additional particles are attracted in case of pushers, the neighbouring particles are repelled in case of neutral swimmers and pullers. Hence the rings show the expected shrinking and swelling behaviours, see again Fig. 4a. The velocity dependence of the inverse radius of gyration for pushers is non-mononotic. This is a result of an induced torque on each particle, Fig. 6a, which leads to a ring configuration where the dipoles point outwards. This state is non-favorable for magnetic dipoles and, therefore, even pushers show a swelling behaviour for velocities v/v0>2.7.

View Article: PubMed Central - PubMed

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.

No MeSH data available.