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Emergent vortices in populations of colloidal rollers.

Bricard A, Caussin JB, Das D, Savoie C, Chikkadi V, Shitara K, Chepizhko O, Peruani F, Saintillan D, Bartolo D - Nat Commun (2015)

Bottom Line: Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking.Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex.Combining physical experiments and numerical simulations, we elucidate this collective behaviour.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physique de l'Ecole Normale Supérieure de Lyon, Université de Lyon and CNRS, 46, allée d'Italie, Lyon F-69007, France.

ABSTRACT
Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behaviour. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries.

No MeSH data available.


Related in: MedlinePlus

Experimental setup.(a) Sketch of the setup. Five5-micrometre PMMA colloids roll in a microchannel made of two ITO-coated glass slides assembled with double-sided scotch tape. An electrokinetic flow confines the rollers at the centre of the device in a circular chamber of radius Rc. (b) Superimposed fluorescence pictures of a dilute ensemble of rollers (E0/EQ=1.1, φ0=6 × 10−3). The colloids propel only inside a circular disc of radius Rc=1 mm and follow persistent random walks.
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f1: Experimental setup.(a) Sketch of the setup. Five5-micrometre PMMA colloids roll in a microchannel made of two ITO-coated glass slides assembled with double-sided scotch tape. An electrokinetic flow confines the rollers at the centre of the device in a circular chamber of radius Rc. (b) Superimposed fluorescence pictures of a dilute ensemble of rollers (E0/EQ=1.1, φ0=6 × 10−3). The colloids propel only inside a circular disc of radius Rc=1 mm and follow persistent random walks.

Mentions: The experimental setup is fully described in the Methods section and in Fig. 1a,b. Briefly, we use colloidal rollers powered by the Quincke electrorotation mechanism as thoroughly explained in ref. 11. An electric field E0 is applied to insulating colloidal beads immersed in a conducting fluid. Above a critical field amplitude EQ, the symmetry of the electric charge distribution at the bead surface is spontaneously broken. As a result, a net electric torque acts on the beads causing them to rotate at a constant rate around a random axis transverse to the electric field282930. When the colloids sediment, or are electrophoretically driven, onto one of the two electrodes, rotation is converted into a net rolling motion along a random direction. Here, we use poly(methyl methacrylate) (PMMA) spheres of radius a=2.4 μm immersed in a hexadecane solution.


Emergent vortices in populations of colloidal rollers.

Bricard A, Caussin JB, Das D, Savoie C, Chikkadi V, Shitara K, Chepizhko O, Peruani F, Saintillan D, Bartolo D - Nat Commun (2015)

Experimental setup.(a) Sketch of the setup. Five5-micrometre PMMA colloids roll in a microchannel made of two ITO-coated glass slides assembled with double-sided scotch tape. An electrokinetic flow confines the rollers at the centre of the device in a circular chamber of radius Rc. (b) Superimposed fluorescence pictures of a dilute ensemble of rollers (E0/EQ=1.1, φ0=6 × 10−3). The colloids propel only inside a circular disc of radius Rc=1 mm and follow persistent random walks.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4557359&req=5

f1: Experimental setup.(a) Sketch of the setup. Five5-micrometre PMMA colloids roll in a microchannel made of two ITO-coated glass slides assembled with double-sided scotch tape. An electrokinetic flow confines the rollers at the centre of the device in a circular chamber of radius Rc. (b) Superimposed fluorescence pictures of a dilute ensemble of rollers (E0/EQ=1.1, φ0=6 × 10−3). The colloids propel only inside a circular disc of radius Rc=1 mm and follow persistent random walks.
Mentions: The experimental setup is fully described in the Methods section and in Fig. 1a,b. Briefly, we use colloidal rollers powered by the Quincke electrorotation mechanism as thoroughly explained in ref. 11. An electric field E0 is applied to insulating colloidal beads immersed in a conducting fluid. Above a critical field amplitude EQ, the symmetry of the electric charge distribution at the bead surface is spontaneously broken. As a result, a net electric torque acts on the beads causing them to rotate at a constant rate around a random axis transverse to the electric field282930. When the colloids sediment, or are electrophoretically driven, onto one of the two electrodes, rotation is converted into a net rolling motion along a random direction. Here, we use poly(methyl methacrylate) (PMMA) spheres of radius a=2.4 μm immersed in a hexadecane solution.

Bottom Line: Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking.Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex.Combining physical experiments and numerical simulations, we elucidate this collective behaviour.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire de Physique de l'Ecole Normale Supérieure de Lyon, Université de Lyon and CNRS, 46, allée d'Italie, Lyon F-69007, France.

ABSTRACT
Coherent vortical motion has been reported in a wide variety of populations including living organisms (bacteria, fishes, human crowds) and synthetic active matter (shaken grains, mixtures of biopolymers), yet a unified description of the formation and structure of this pattern remains lacking. Here we report the self-organization of motile colloids into a macroscopic steadily rotating vortex. Combining physical experiments and numerical simulations, we elucidate this collective behaviour. We demonstrate that the emergent-vortex structure lives on the verge of a phase separation, and single out the very constituents responsible for this state of polar active matter. Building on this observation, we establish a continuum theory and lay out a strong foundation for the description of vortical collective motion in a broad class of motile populations constrained by geometrical boundaries.

No MeSH data available.


Related in: MedlinePlus