Active turbulence in a gas of self-assembled spinners

Kokot, Gašper; Das, Shibananda; Winkler, Roland G.; Gompper, Gerhard; Aranson, Igor S.; Snezhko, Alexey

doi:10.1073/pnas.1710188114

Cited by 150 publications

(125 citation statements)

References 52 publications

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“…, 14] and sperm cells [4,15] near surfaces, and magnetotactic bacteria in rotating fields [16,17]. Artificial chiral active systems have also been developed, such as colloids [18][19][20][21][22][23][24], millimeter-scale magnets [25,26] and rotating granular particles [27][28][29][30]. Multiple numerical and theoretical studies on chiral active fluid have been carried out [27,[31][32][33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Robust boundary flow in chiral active fluid

et al. 2020

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We perform experiments on an active chiral fluid system of self-spinning rotors in confining boundary. Along the boundary, actively rotating rotors collectively drives a unidirectional material flow. We systematically vary rotor density and boundary shape; boundary flow robustly emerges under all conditions. Flow strength initially increases then decreases with rotor density (quantified by area fraction φ); peak strength appears around a density φ = 0.65. Boundary curvature plays an important role: flow near a concave boundary is stronger than that near a flat or convex boundary in the same confinements. Our experimental results in all cases can be reproduced by a continuum theory with single free fitting parameter, which describes the frictional property of the boundary.Our results support the idea that boundary flow in active chiral fluid is topologically protected; such robust flow can be used to develop materials with novel functions. *

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Section: Introductionmentioning

confidence: 99%

Robust boundary flow in chiral active fluid

et al. 2020

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“…One can directly observe from these results that the dissipative/reactive nature of the different terms may change during the elimination process. In the specific case considered here, η c was clearly related to dissipative terms in the general formalism; see (18). However, after elimination of angular momentum, it emerges that η c is related to a strictly reactive term in (43), but contributes to both reactive and dissipative terms in (44).…”

Section: The Limit Of Vanishing Moment Of Inertiamentioning

confidence: 77%

“…particles are spinning under an external rotating magnetic field [17,18]; this can be modelled by an external body torque t in the direction of spin. Next, we shall derive the relationship between the internal body torque, s, and the stress tensor, s. Consider a co-moving finite parcel of fluid occupying a region V(t).…”

Section: Intrinsicmentioning

confidence: 99%

“…Furthermore, there is growing literature on systems of 'active' spinners [15][16][17][18]. In these systems, particles (of the same species) are spinning in the same direction-either clockwise or anti-clockwise on a twodimensional plane.…”

Section: Introductionmentioning

confidence: 99%

“…In these systems, particles (of the same species) are spinning in the same direction-either clockwise or anti-clockwise on a twodimensional plane. These spinners can be driven by an external field such as a rotating magnetic field [17,18] or can be active because of internal motors that interact with a substrate. Our hydrodynamic theory can capture the dynamics of 'active' spinners by including the external field as a body torque-similar to treating gravity as a body force.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Chiral active matter: microscopic ‘torque dipoles’ have more than one hydrodynamic description

2019

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Many biological systems, such as bacterial suspensions and actomyosin networks, form polar liquid crystals. These systems are 'active' or far-from-equilibrium, due to local forcing of the solvent by the constituent particles. In many cases the source of activity is chiral; since forcing is internally generated, some sort of 'torque dipole' is then present locally. But it is not obvious how 'torque dipoles' should be encoded in the hydrodynamic equations that describe the system at the continuum level: different authors have arrived at contradictory conclusions on this issue. In this work, we resolve the paradox by presenting a careful derivation, from linear irreversible thermodynamics, of the general equations of motion of a single-component chiral active fluid with spin degrees of freedom. We find that there is no unique hydrodynamic description for such a fluid in the presence of torque dipoles of a given strength. Instead, at least three different hydrodynamic descriptions emerge, depending on whether we decompose each torque dipole as two point torques, two force pairs, or one point torque and one force pair-where point torques create internal angular momenta of the chiral bodies (spin), whereas force pairs impart centre of mass motion that contributes to fluid velocity. By considering a general expansion of the Onsager coefficients, we also derive a new shear-elongation parameter and crosscoupling viscosity, which can lead to unpredicted phenomena even in passive polar liquid crystals. Finally, elimination of the angular variables gives an effective polar hydrodynamics with renormalized active stresses, viscosities and kinetic coefficients. Remarkably, this can include a direct contribution of chiral activity to the equation of motion for the polar order parameter, which survives even in 'dry' active systems where the fluid velocity is set to zero.

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Supercolloidal Spinners: Complex Active Particles for Electrically Powered and Switchable Rotation

Shields

Han

et al. 2018

Adv Funct Materials

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A class of supercolloidal particles that controllably spin about their central axis in AC electric fields is reported. The rational design of these "microspinners" enables their rotation in a switchable manner, which gives rise to several interesting and programmable behaviors. It is shown that due to their complex shape and discrete metallic patches on their surfaces, these microspinners convert electrical energy into active motion via the interplay of four mechanisms at different electric field frequency ranges. These mechanisms of rotation include (in order of increasing frequency): electrohydrodynamic flows, reversed electrohydrodynamic flows, induced charge electrophoresis, and self-dielectrophoresis. As the primary mechanism powering their motion transitions from one phenomenon to the next, these microspinners display three directional spin inversions (i.e., from clockwise to anticlockwise, or vice versa). To understand the mechanisms involved, this experimental study is coupled with scaling analyses. Due to their frequency-switchable rotation, these microspinners have potential for applications such as interlocking gears in colloidal micromachines. Moreover, the principles used to power their switchable motion can be extended to design other types of supercolloidal particles that harvest electrical energy for motion via multiple electrokinetic mechanisms.

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Active turbulence in a gas of self-assembled spinners

Cited by 150 publications

References 52 publications

Robust boundary flow in chiral active fluid

Robust boundary flow in chiral active fluid

Chiral active matter: microscopic ‘torque dipoles’ have more than one hydrodynamic description

Supercolloidal Spinners: Complex Active Particles for Electrically Powered and Switchable Rotation

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