Active colloidal molecules

Löwen, Hartmut

doi:10.1209/0295-5075/121/58001

Cited by 68 publications

(60 citation statements)

References 101 publications

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“…Besides a range of theoretical studies focusing on motility-induced phase separation in active-passive mixtures [11][12][13][14] occurring at moderate densities, recent experiments [15][16][17][18][19] have observed the formation of various self-assembled structures even at very low active particle densities. Since these structures resemble those of ordinary molecules, the emerging clusters are called heteronuclear active colloidal molecules [20][21][22][23][24][25][26][27][28][29][30][31][32][33] . Ref.…”

Section: Introductionmentioning

confidence: 99%

Clustering-induced velocity-reversals of active colloids mixed with passive particles

Hauke

Löwen

Liebchen

2020

The Journal of Chemical Physics

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Recent experiments have shown that colloidal suspensions can spontaneously self-assemble into dense clusters of various internal structures, sizes and dynamical properties when doped with active Janus particles. Characteristically, these clusters move ballistically during their formation, but dynamically revert their velocity and temporarily move opposite to the self-propulsion direction of the Janus particles they contain. Here we explore a simple effective model of colloidal mixtures which allows reproducing most aspects seen in experiments, including the morphology and the velocity-reversal of the clusters. We attribute the latter to the nonreciprocal phoretic attractions of the passive particles to the active colloids' caps, taking place even at close contact and pushing the active particles backwards. When the phoretic interactions are repulsive, in turn, they cause dynamical aggregation of passive colloids in the chemical density minima produced by the active particles, as recently seen in experiments; in other parameter regimes they induce travelling fronts of active particles pursued by passive ones coexisting with an active gas.arXiv:1909.09578v1 [cond-mat.soft]

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Section: Introductionmentioning

confidence: 99%

Clustering-induced velocity-reversals of active colloids mixed with passive particles

Hauke

Löwen

Liebchen

2020

The Journal of Chemical Physics

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“…Out of the biological realm, it is even possible to realize synthetic active colloidal polymers [6], such as chains of colloids uniformly coated with catalytic particles [7] becoming active when immersed in a solution of H 2 O 2 . The "activation" of Janus particles can be even controlled by external fields, and, in particular, the spontaneous formation of chains of particles has been experimentally observed upon tuning the frequencies of an AC electric field [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

How a local active force modifies the structural properties of polymers

2020

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We study the dynamics of a polymer, described as a variant of a Rouse chain, driven by an active terminal monomer (head). The local active force induces a transition from a globule-like to an elongated state, as revealed by the study of the end-to-end distance, whose variance is analytically predicted under suitable approximations. The change in the relaxation times of the Rouse-modes produced by the local self-propulsion is consistent with the transition from globule to elongated conformations. Moreover also the bond-bond spatial correlation for the chain head results to be affected and a gradient of over-stretched bonds along the chain is observed. We compare our numerical results both with the phenomenological stiff-polymer theory and several analytical predictions in the Rouse-chain approximation. arXiv:1911.06688v2 [cond-mat.stat-mech]

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“…In Appendix B, we show some analytical calculations for the distances traveled by a microswimmer during reorientation. We then quantify in Appendix C the fluid-mediated hydrodynamic interactions between colloidal particles which could serve as a basis for future investigations of the behavior of special particle-based microswimmer models [134][135][136][137][138][139][140][141][142][143][144] .…”

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Dynamics of a simple model microswimmer in an anisotropic fluid: Implications for alignment behavior and active transport in a nematic liquid crystal

Daddi-Moussa-Ider

Menzel

2018

Phys. Rev. Fluids

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Several recent experiments investigate the orientational and transport behavior of self-driven bacteria and colloidal particles in nematic liquid crystals. Correspondingly, we study theoretically the dynamics of a minimal model microswimmer in a uniaxially anisotropic fluid. As a first step, the hydrodynamic Green's function providing the resulting fluid flow in response to a localized force acting on the anisotropic fluid is derived analytically. On this basis, the behavior of both puller-and pusher-type microswimmers in the anisotropic fluid is analyzed. Depending on the propulsion mechanism and the relative magnitude of different involved viscosities, we find alignment of the swimmers parallel or perpendicular to the anisotropy axis. Particularly, also an oblique alignment is identified under certain circumstances. The observed swimmer reorientation results from the hydrodynamic coupling between the self-induced fluid flow and the anisotropy of the surrounding fluid, which distorts the self-generated flow field. We support parts of our results by a simplified linear stability analysis. Our theoretical predictions are in qualitative agreement with recent experimental observations on swimming bacteria in nematic liquid crystals. They support the objective of utilizing the, possibly switchable, anisotropy of a host fluid to guide individual microswimmers and active particles along a requested path, enabling controlled active transport. I. INTRODUCTIONActive particles have the ability to move autonomously in a surrounding fluid by converting energy into directed motion. Artificial self-propelled nano-and microscale machines hold great promise for future medical research to reach otherwise inaccessible areas of the body to perform delicate and precise tasks. Prospective biomedical applications are precision nanosurgery, biopsy, and transport of radioactive substances to tumor areas and inflammation sites 1-3 . Over the last few decades, significant research efforts have been devoted to investigate the behavior of self-propelling active particles due to their importance and relevance as model systems for transport and locomotion in the micro-and nano-scale world; for recent reviews see Refs. 4-12. Unusual macroscopic signatures and intriguing spatiotemporal patterns emerge from the interaction between several active particles. For instance, the onset of collective motion 13-19 , formation of dynamic clusters 20-26 , wave patterns 27-30 , laning 31-35 , motility-induced phase separation 36-41 , swarming 42-44 , and active turbulence 45-52 are observed. In many cases, artificial self-driven particles and swimming microorganisms have to propel through complex fluids, such as polymer gels and viscoelastic microemulsions [53][54][55][56][57][58][59][60][61][62][63] . Notable examples include sperm navigation through the mammalian female reproductive tract 64,65 , bacteria locomotion in biofilm matrices composed of extracellular polymeric substances 66,67 , nematode movement in soil 68,69 , and the motion of synthetic mic...

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Active colloidal molecules

Cited by 68 publications

References 101 publications

Clustering-induced velocity-reversals of active colloids mixed with passive particles

Clustering-induced velocity-reversals of active colloids mixed with passive particles

How a local active force modifies the structural properties of polymers

Dynamics of a simple model microswimmer in an anisotropic fluid: Implications for alignment behavior and active transport in a nematic liquid crystal

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