Stability of a Dumbbell Micro-Swimmer

Ishikawa, Takuji

doi:10.3390/mi10010033

Cited by 16 publications

(11 citation statements)

References 40 publications

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“…The squirmer model has been generalized in various ways e.g. to account for generalshapes [220], non-symmetric slip-velocities [102] (see above), deformable spheres [221], spheroidal shapes [222,223], squirmer dumbbells [224,225] and squirmer rods [226]. Detailed simulations of two squirmers using boundary element methods have been performed in [219] which have been complemented with analytical calculations confirming the expected form of the far-field interactions and in particular also the applicability of lubrication theory at interparticle distances which are short compared to the particle size [219].…”

Section: Simulations Of Interacting Squirmersmentioning

confidence: 99%

Which interactions dominate in active colloids?

Liebchen

Löwen

2019

The Journal of Chemical Physics

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Despite a mounting evidence that the same gradients which active colloids use for swimming, induce important crossinteractions (phoretic interaction), they are still ignored in most many-body descriptions, perhaps to avoid complexity and a zoo of unknown parameters. Here we derive a simple model, which reduces phoretic far-field interactions to a pair-interaction whose strength is mainly controlled by one genuine parameter (swimming speed). The model suggests that phoretic interactions are generically important for autophoretic colloids (unless effective screening of the phoretic fields is strong) and should dominate over hydrodynamic interactions for the typical case of half-coating and moderately nonuniform surface mobilities. Unlike standard minimal models, but in accordance with canonical experiments, our model generically predicts dynamic clustering in active colloids at low density. This suggests that dynamic clustering can emerge from the interplay of screened phoretic attractions and active diffusion.

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Section: Simulations Of Interacting Squirmersmentioning

confidence: 99%

Which interactions dominate in active colloids?

Liebchen

Löwen

2019

The Journal of Chemical Physics

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“…The swimming behavior of athermal squirmer dumbbells has been investigated by the boundary integral method, 229 where, in this context, swimming refers to ballistic motion. The calculations show a strong effect of FIG.…”

Section: A Linear Squirmer Assembliesmentioning

confidence: 99%

“…By introducing a (short) bond, which restricts an independent rotation, circular trajectories for pushers and stable side-by-side swimming for pullers can be obtained. 229 Athermal squirmer lack rotational diffusion, thus, absence of locomotion of freely rotating spheres in a dumbbell is a consequence of the missing thermal fluctuations of the fluid. Such fluctuations can be taken into account by mesoscale hydrodynamic simulations, e.g., the multiparticle collision dynamics (MPC) method, [189][190][191] and locomotion is obtained.…”

Section: A Linear Squirmer Assembliesmentioning

confidence: 99%

The physics of active polymers and filaments

Winkler,

Gompper

2020

Preprint

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Active matter agents consume internal energy or extract energy from the environment for locomotion and force generation. Already rather generic models, such as ensembles of active Brownian particles, exhibit phenomena, which are absent at equilibrium, in particular motility-induced phase separation and collective motion. Further intriguing nonequilibrium effects emerge in assemblies of bound active agents as in linear polymers or filaments. The interplay of activity and conformational degrees of freedom gives rise to novel structural and dynamical features of individual polymers as well as in interacting ensembles. Such outof-equilibrium polymers are an integral part of living matter, ranging from biological cells with filaments propelled by motor proteins in the cytoskeleton, and RNA/DNA in the transcription process, to long swarming bacteria and worms such as Proteus mirabilis and Caenorhabditis elegans, respectively. Even artificial active polymers have been synthesized. The emergent properties of active polymers or filaments depend on the coupling of the active process to their conformational degrees of freedom, aspects which are addressed in this article. The theoretical models for tangentially and isotropically self-propelled or active-bath driven polymers are presented, both in presence and absence of hydrodynamic interactions. The consequences for their conformational and dynamical properties are examined, emphasizing the strong influence of the coupling between activity and hydrodynamic interactions. Particular features of emerging phenomena, induced by steric and hydrodynamic interactions, are highlighted. Various important, yet theoretically unexplored, aspects are featured and future challenges are discussed.

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Section: Introductionmentioning

confidence: 99%

“…Apart from a spherical squirmer, a squirmer dumbbell assembled by two squirmers has also attracted the attention of researchers since it is a minimal model of linked microswimmers and forms the basis for constructing more complex assemblies such as autonomous micro-robots (Ishikawa, 2019) and new functional soft materials (Cates & MacKintosh 2011; Winkler & Gompper 2020). Recently, Ishikawa (2019) has studied the stability of a squirmer dumbbell swimming in a bulk fluid. His results show that a dumbbell squirmer could not achieve a stable forward swimming in the far field without an external torque, and when the aft squirmer is a strong pusher, fore and aft swimming is stable, and swimming speed increases significantly.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamics of an inertial squirmer and squirmer dumbbell in a tube

Ouyang

Lin

et al. 2022

J. Fluid Mech.

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We study the hydrodynamics of a spherical and dumbbell-shaped microswimmer in a tube. Combined with a squirmer model generating tangential surface waves for self-propulsion, a direct-forcing fictitious domain method is employed to simulate the swimming of the microswimmers. We perform the simulations by considering the variations of the swimming Reynolds numbers (Re), the blockage ratios (κ) and the relative distances (ds) between the squirmers of the dumbbell. The results show that the squirmer dumbbell weakens the inertia effects of the fluid more than an individual squirmer. The constrained tube can speed up an inertial pusher (propelled from the rear) and an inertia pusher dumbbell; a greater distance ds results in a slower speed of an inertial pusher dumbbell but a faster speed of an inertial puller (propelled from the front) dumbbell. We also illustrate the swimming stability of a puller (stable) and pusher (unstable) swimming in the tube at Re = 0. At a finite Re, we find that the inertia and the tube constraint competitively affect the swimming stability of the squirmers and squirmer dumbbells. The puller and puller dumbbells swimming in the tube become unstable with increasing Re, whereas an unstable–stable–unstable evolution is found for the pusher and pusher dumbbells. With increasing κ, the puller and puller dumbbells become stable while the pusher and pusher dumbbells become unstable. In addition, we find that a greater ds yields a higher hydrodynamic efficiency η of the inertial squirmer dumbbell.

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Stability of a Dumbbell Micro-Swimmer

Cited by 16 publications

References 40 publications

Which interactions dominate in active colloids?

Which interactions dominate in active colloids?

The physics of active polymers and filaments

Hydrodynamics of an inertial squirmer and squirmer dumbbell in a tube

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