Symmetric Mixtures of Pusher and Puller Microswimmers Behave as Noninteracting Suspensions
(2020) In Physical Review Letters 125(1).- Abstract
Suspensions of rear- and front-actuated microswimmers immersed in a fluid, known respectively as "pushers"and "pullers,"display qualitatively different collective behaviors: beyond a characteristic density, pusher suspensions exhibit a hydrodynamic instability leading to collective motion known as active turbulence, a phenomenon which is absent for pullers. In this Letter, we describe the collective dynamics of a binary pusher-puller mixture using kinetic theory and large-scale particle-resolved simulations. We derive and verify an instability criterion, showing that the critical density for active turbulence moves to higher values as the fraction χ of pullers is increased and disappears for χ≥0.5. We then show analytically and... (More)
Suspensions of rear- and front-actuated microswimmers immersed in a fluid, known respectively as "pushers"and "pullers,"display qualitatively different collective behaviors: beyond a characteristic density, pusher suspensions exhibit a hydrodynamic instability leading to collective motion known as active turbulence, a phenomenon which is absent for pullers. In this Letter, we describe the collective dynamics of a binary pusher-puller mixture using kinetic theory and large-scale particle-resolved simulations. We derive and verify an instability criterion, showing that the critical density for active turbulence moves to higher values as the fraction χ of pullers is increased and disappears for χ≥0.5. We then show analytically and numerically that the two-point hydrodynamic correlations of the 1:1 mixture are equal to those of a suspension of noninteracting swimmers. Strikingly, our numerical analysis furthermore shows that the full probability distribution of the fluid velocity fluctuations collapses onto the one of a noninteracting system at the same density, where swimmer-swimmer correlations are strictly absent. Our results thus indicate that the fluid velocity fluctuations in 1:1 pusher-puller mixtures are exactly equal to those of the corresponding noninteracting suspension at any density, a surprising cancellation with no counterpart in equilibrium long-range interacting systems.
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- author
- Bárdfalvy, Dóra LU ; Anjum, Shan ; Nardini, Cesare ; Morozov, Alexander and Stenhammar, Joakim LU
- organization
- publishing date
- 2020
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Physical Review Letters
- volume
- 125
- issue
- 1
- article number
- 018003
- publisher
- American Physical Society
- external identifiers
-
- scopus:85087885553
- pmid:32678625
- ISSN
- 0031-9007
- DOI
- 10.1103/PhysRevLett.125.018003
- language
- English
- LU publication?
- yes
- id
- 0792da1e-0e00-4339-8273-80eeef110d24
- date added to LUP
- 2020-07-29 11:24:23
- date last changed
- 2024-07-10 19:39:43
@article{0792da1e-0e00-4339-8273-80eeef110d24,
abstract = {{<p>Suspensions of rear- and front-actuated microswimmers immersed in a fluid, known respectively as "pushers"and "pullers,"display qualitatively different collective behaviors: beyond a characteristic density, pusher suspensions exhibit a hydrodynamic instability leading to collective motion known as active turbulence, a phenomenon which is absent for pullers. In this Letter, we describe the collective dynamics of a binary pusher-puller mixture using kinetic theory and large-scale particle-resolved simulations. We derive and verify an instability criterion, showing that the critical density for active turbulence moves to higher values as the fraction χ of pullers is increased and disappears for χ≥0.5. We then show analytically and numerically that the two-point hydrodynamic correlations of the 1:1 mixture are equal to those of a suspension of noninteracting swimmers. Strikingly, our numerical analysis furthermore shows that the full probability distribution of the fluid velocity fluctuations collapses onto the one of a noninteracting system at the same density, where swimmer-swimmer correlations are strictly absent. Our results thus indicate that the fluid velocity fluctuations in 1:1 pusher-puller mixtures are exactly equal to those of the corresponding noninteracting suspension at any density, a surprising cancellation with no counterpart in equilibrium long-range interacting systems. </p>}},
author = {{Bárdfalvy, Dóra and Anjum, Shan and Nardini, Cesare and Morozov, Alexander and Stenhammar, Joakim}},
issn = {{0031-9007}},
language = {{eng}},
number = {{1}},
publisher = {{American Physical Society}},
series = {{Physical Review Letters}},
title = {{Symmetric Mixtures of Pusher and Puller Microswimmers Behave as Noninteracting Suspensions}},
url = {{http://dx.doi.org/10.1103/PhysRevLett.125.018003}},
doi = {{10.1103/PhysRevLett.125.018003}},
volume = {{125}},
year = {{2020}},
}