Focusing by blocking: Repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes

Menzel, Andreas M.

doi:10.1209/0295-5075/110/38005

Cited by 7 publications

(13 citation statements)

References 54 publications

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“…At low Péclet numbers, which means low magnitude of the active forces, the microswimmers propel outwards, where in a final stationary state they form a ring-like density profile. This effect remains when hydrodynamic interactions are switched off in the numerical calculations as reported in different frameworks previously [110,111,113]. Increasing the Péclet number and including hydrodynamic interactions, the numerical evaluation of the DDFT shows a breaking of rotational symmetry.…”

Section: Discussionmentioning

confidence: 73%

“…In particular, this concerns the time evolution towards a final steady state when self-propulsion is suddenly switched on in an initially equilibrated system. Such a behavior could for instance be realized in experiments using light-activated microswimmers [35,36,[106][107][108][109][110]. Here, we present numerical results for two-dimensional arrangements.…”

Section: Planar Trapped Microswimmer Arrangementsmentioning

confidence: 95%

“…In this sense, the potential blocks the swimmer motion in the final steady state [112]. It takes a typical rotational diffusion time scale until a swimmer can reorient and leave the trapping location, before it propels towards another location on the high-density ring [110,111].…”

Section: Planar Trapped Microswimmer Arrangementsmentioning

confidence: 99%

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Dynamical density functional theory for microswimmers

Menzel

Saha

Hoell

et al. 2016

The Journal of Chemical Physics

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147

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Dynamical density functional theory (DDFT) has been successfully derived and applied to describe on the one hand passive colloidal suspensions, including hydrodynamic interactions between individual particles. On the other hand, active "dry" crowds of self-propelled particles have been characterized using DDFT. Here we go one essential step further and combine these two approaches. We establish a DDFT for active microswimmer suspensions. For this purpose, simple minimal model microswimmers are introduced. These microswimmers self-propel by setting the surrounding fluid into motion. They hydrodynamically interact with each other through their actively self-induced fluid flows and via the common "passive" hydrodynamic interactions. An effective soft steric repulsion is also taken into account. We derive the DDFT starting from common statistical approaches. Our DDFT is then tested and applied by characterizing a suspension of microswimmers the motion of which is restricted to a plane within a three-dimensional bulk fluid. Moreover, the swimmers are confined by a radially symmetric trapping potential. In certain parameter ranges, we find rotational symmetry breaking in combination with the formation of a "hydrodynamic pumping state", which has previously been observed in the literature as a result of particle-based simulations. An additional instability of this pumping state is revealed.

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Section: Discussionmentioning

confidence: 73%

Section: Planar Trapped Microswimmer Arrangementsmentioning

confidence: 95%

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Dynamical density functional theory for microswimmers

Menzel

Saha

Hoell

et al. 2016

The Journal of Chemical Physics

Self Cite

147

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show abstract

“…It will not stay in the potential minimum. Instead, it moves against and climbs up the potential walls [35,51,113,114], at least as long as it does not reorient. Being able to work against the walls requires an effective active drive of the swimmer.…”

Section: Deformable Model Microswimmersmentioning

confidence: 99%

“…This includes the individual dynamics of particles with complex shape [7][8][9], as well as cases of self-rotation [9][10][11][12][13][14][15]. Furthermore, the collective behavior of many such interacting particles has been explored [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. Collections of self-propelled particles in liquid environment exhibit fascinating and complex nonequilibrium phenomena emerging from self-organization, where hydrodynamic interactions can play a significant role [11,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52].…”

Section: Introductionmentioning

confidence: 99%

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

2016

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Deformability is a central feature of many types of microswimmers, e.g. for artificially generated self-propelled droplets. Here, we analyze deformable bead-spring microswimmers in an externally imposed solvent flow field as simple theoretical model systems. We focus on their behavior in a circular swirl flow in two spatial dimensions. Linear (straight) two-bead swimmers are found to circle around the swirl with a slight drift to the outside with increasing activity. In contrast to that, we observe for triangular three-bead or square-like four-bead swimmers a tendency of being drawn into the swirl and finally getting drowned, although a radial inward component is absent in the flow field. During one cycle around the swirl, the self-propulsion direction of an active triangular or square-like swimmer remains almost constant, while their orbits become deformed exhibiting an "egg-like" shape. Over time, the swirl flow induces slight net rotations of these swimmer types, which leads to net rotations of the egg-shaped orbits. Interestingly, in certain cases, the orbital rotation changes sense when the swimmer approaches the flow singularity. Our predictions can be verified in real-space experiments on artificial microswimmers.

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Multi-species dynamical density functional theory for microswimmers: Derivation, orientational ordering, trapping potentials, and shear cells

Hoell

Löwen

Menzel

2019

The Journal of Chemical Physics

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Microswimmers typically operate in complex environments. In biological systems, often diverse species are simultaneously present and interact with each other. Here, we derive a (time-dependent) particle-scale statistical description, namely a dynamical density functional theory, for such multi-species systems, extending existing works on one-component microswimmer suspensions. In particular, our theory incorporates the effect of external potentials, but also steric and hydrodynamic interactions between swimmers. For the latter, a previously introduced force-dipole-based minimal (pusher or puller) microswimmer model is used. As a limiting case of our theory, mixtures of hydrodynamically interacting active and passive particles are captured as well. After deriving the theory, we apply it to different planar swimmer configurations. First, these are binary pusher-puller mixtures in external traps. In the considered situations, we find that the majority species imposes its behavior on the minority species. Second, for unconfined binary pusher-puller mixtures, the linear stability of an orientationally disordered state against the emergence of global polar orientational order (and thus emergent collective motion) is tested analytically. Our statistical approach predicts, qualitatively in line with previous particle-based computer simulations, a threshold for the fraction of pullers and for their propulsion strength that lets overall collective motion arise. Third, we let driven passive colloidal particles form the boundaries of a shear cell, with confined active microswimmers on their inside. Driving the passive particles then effectively imposes shear flows, which persistently acts on the inside microswimmers. Their resulting behavior reminds of the one of circle swimmers, though with varying swimming radii. arXiv:1904.07277v2 [cond-mat.soft]

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Focusing by blocking: Repeatedly generating central density peaks in self-propelled particle systems by exploiting diffusive processes

Cited by 7 publications

References 54 publications

Dynamical density functional theory for microswimmers

Dynamical density functional theory for microswimmers

Getting drowned in a swirl: Deformable bead-spring model microswimmers in external flow fields

Multi-species dynamical density functional theory for microswimmers: Derivation, orientational ordering, trapping potentials, and shear cells

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