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Chan CW, Yang Z, Gan Z, Zhang R. Interplay of chemotactic force, Péclet number, and dimensionality dictates the dynamics of auto-chemotactic chiral active droplets. J Chem Phys 2024; 161:014904. [PMID: 38953449 DOI: 10.1063/5.0207355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Accepted: 05/31/2024] [Indexed: 07/04/2024] Open
Abstract
In living and synthetic active matter systems, the constituents can self-propel and interact with each other and with the environment through various physicochemical mechanisms. Among these mechanisms, chemotactic and auto-chemotactic effects are widely observed. The impact of (auto-)chemotactic effects on achiral active matter has been a recent research focus. However, the influence of these effects on chiral active matter remains elusive. Here, we develop a Brownian dynamics model coupled with a diffusion equation to examine the dynamics of auto-chemotactic chiral active droplets in both quasi-two-dimensional (2D) and three-dimensional (3D) systems. By quantifying the droplet trajectory as a function of the dimensionless Péclet number and chemotactic strength, our simulations well reproduce the curling and helical trajectories of nematic droplets in a surfactant-rich solution reported by Krüger et al. [Phys. Rev. Lett. 117, 048003 (2016)]. The modeled curling trajectory in 2D exhibits an emergent chirality, also consistent with the experiment. We further show that the geometry of the chiral droplet trajectories, characterized by the pitch and diameter, can be used to infer the velocities of the droplet. Interestingly, we find that, unlike the achiral case, the velocities of chiral active droplets show dimensionality dependence: its mean instantaneous velocity is higher in 3D than in 2D, whereas its mean migration velocity is lower in 3D than in 2D. Taken together, our particle-based simulations provide new insights into the dynamics of auto-chemotactic chiral active droplets, reveal the effects of dimensionality, and pave the way toward their applications, such as drug delivery, sensors, and micro-reactors.
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Affiliation(s)
- Chung Wing Chan
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR
- Thrust of Advanced Materials, and Guangzhou Municipal Key Laboratory of Materials Informatics, The Hong Kong University of Science and Technology (Guangzhou), Guangdong, China
| | - Zheng Yang
- Thrust of Advanced Materials, and Guangzhou Municipal Key Laboratory of Materials Informatics, The Hong Kong University of Science and Technology (Guangzhou), Guangdong, China
- Interdisciplinary Programs Office, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR
| | - Zecheng Gan
- Thrust of Advanced Materials, and Guangzhou Municipal Key Laboratory of Materials Informatics, The Hong Kong University of Science and Technology (Guangzhou), Guangdong, China
- Department of Mathematics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR
| | - Rui Zhang
- Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR
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2
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Saavedra R, Gompper G, Ripoll M. Swirling Due to Misaligned Perception-Dependent Motility. PHYSICAL REVIEW LETTERS 2024; 132:268301. [PMID: 38996279 DOI: 10.1103/physrevlett.132.268301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Accepted: 05/21/2024] [Indexed: 07/14/2024]
Abstract
A system of particles with motility variable in terms of a vision-type of perception is investigated by a combination of Langevin dynamics simulations in two-dimensional systems and an analytical approach based on conservation law principles. Persistent swirling with predetermined direction is here induced by differentiating the self-propulsion direction and the perception cone axis. Clusters can have a fluidlike center with a rotating outer layer or display a solidlike rotation driven by the outer layer activity. Discontinuous motility with misaligned perception might therefore serve as a powerful self-organization strategy in microrobots.
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3
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Cao J, Wu J, Hou Z. Quorum sensing-induced transition from colloidal waves to Turing-like patterns in chemorepulsive active colloids. Phys Chem Chem Phys 2024; 26:7783-7793. [PMID: 38375586 DOI: 10.1039/d3cp04910h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
The study of active systems, especially in the presence of a chemical background field, is garnering significant attention. Traditionally, the self-propelled velocity of active colloids was assumed to be constant, independent of the local density of colloids. In this work, we introduce a chemotactic active system that features quorum sensing (QS), wherein particles act as chemorepellents. Interestingly, these particles lose their activity in regions of high local particle density. Our findings reveal that QS leads to a transition from an oscillatory colloidal wave to a Turing-like pattern, with the observation of an intermediate state. With the variation of the sensing threshold, both the mean oscillation frequency of the system and the number of clusters exhibit non-monotonic dependence. Furthermore, the QS-induced pattern differs markedly from systems without QS, primarily due to the competitive interplay between diffusion and chemotaxis. The dynamics of this phenomenon are explained using a coarse-grained mean field model.
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Affiliation(s)
- Jiaqi Cao
- Department of Chemical Physics & Hefei National Laboratory for Physical Sciences at Microscales, ichEM, University of Science and Technology of China, Hefei, Anhui 230026, China.
| | - Jiaxin Wu
- Department of Chemical Physics & Hefei National Laboratory for Physical Sciences at Microscales, ichEM, University of Science and Technology of China, Hefei, Anhui 230026, China.
| | - Zhonghuai Hou
- Department of Chemical Physics & Hefei National Laboratory for Physical Sciences at Microscales, ichEM, University of Science and Technology of China, Hefei, Anhui 230026, China.
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4
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Ridgway WJM, Dalwadi MP, Pearce P, Chapman SJ. Motility-Induced Phase Separation Mediated by Bacterial Quorum Sensing. PHYSICAL REVIEW LETTERS 2023; 131:228302. [PMID: 38101339 DOI: 10.1103/physrevlett.131.228302] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 10/09/2023] [Indexed: 12/17/2023]
Abstract
We study motility-induced phase separation (MIPS) in living active matter, in which cells interact through chemical signaling, or quorum sensing. In contrast to previous theories of MIPS, our multiscale continuum model accounts explicitly for genetic regulation of signal production and motility. Through analysis and simulations, we derive a new criterion for the onset of MIPS that depends on features of the genetic network. Furthermore, we identify and characterize a new type of oscillatory instability that occurs when gene regulation inside cells promotes motility in higher signal concentrations.
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Affiliation(s)
- Wesley J M Ridgway
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
| | - Mohit P Dalwadi
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
- Department of Mathematics, University College London, London WC1H 0AY, United Kingdom
- Institute for the Physics of Living Systems, University College London, London, United Kingdom
| | - Philip Pearce
- Department of Mathematics, University College London, London WC1H 0AY, United Kingdom
- Institute for the Physics of Living Systems, University College London, London, United Kingdom
| | - S Jonathan Chapman
- Mathematical Institute, University of Oxford, Oxford OX2 6GG, United Kingdom
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5
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Duan Y, Agudo-Canalejo J, Golestanian R, Mahault B. Dynamical Pattern Formation without Self-Attraction in Quorum-Sensing Active Matter: The Interplay between Nonreciprocity and Motility. PHYSICAL REVIEW LETTERS 2023; 131:148301. [PMID: 37862639 DOI: 10.1103/physrevlett.131.148301] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Accepted: 08/31/2023] [Indexed: 10/22/2023]
Abstract
We study a minimal model involving two species of particles interacting via quorum-sensing rules. Combining simulations of the microscopic model and linear stability analysis of the associated coarse-grained field theory, we identify a mechanism for dynamical pattern formation that does not rely on the standard route of intraspecies effective attractive interactions. Instead, our results reveal a highly dynamical phase of chasing bands induced only by the combined effects of self-propulsion and nonreciprocity in the interspecies couplings. Turning on self-attraction, we find that the system may phase separate into a macroscopic domain of such chaotic chasing bands coexisting with a dilute gas. We show that the chaotic dynamics of bands at the interfaces of this phase-separated phase results in anomalously slow coarsening.
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Affiliation(s)
- Yu Duan
- Max Planck Institute for Dynamics and Self-Organization (MPI-DS), 37077 Göttingen, Germany
| | - Jaime Agudo-Canalejo
- Max Planck Institute for Dynamics and Self-Organization (MPI-DS), 37077 Göttingen, Germany
| | - Ramin Golestanian
- Max Planck Institute for Dynamics and Self-Organization (MPI-DS), 37077 Göttingen, Germany
- Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3PU, United Kingdom
| | - Benoît Mahault
- Max Planck Institute for Dynamics and Self-Organization (MPI-DS), 37077 Göttingen, Germany
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6
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Irani E, Mokhtari Z, Zippelius A. Dynamics of Bacteria Scanning a Porous Environment. PHYSICAL REVIEW LETTERS 2022; 128:144501. [PMID: 35476466 DOI: 10.1103/physrevlett.128.144501] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Accepted: 03/09/2022] [Indexed: 06/14/2023]
Abstract
It has recently been reported that bacteria, such as Escherichia coli Bhattacharjee and Datta, Nat. Commun. 10, 2075 (2019).NCAOBW2041-172310.1038/s41467-019-10115-1 and Pseudomonas putida Alirezaeizanjani et al., Sci. Adv. 6, eaaz6153 (2020).SACDAF2375-254810.1126/sciadv.aaz6153, perform distinct modes of motion when placed in porous media as compared to dilute regions or free space. This has led us to suggest an efficient strategy for active particles in a disordered environment: reorientations are suppressed in locally dilute regions and intensified in locally dense ones. Thereby the local geometry determines the optimal path of the active agent and substantially accelerates the dynamics for up to 2 orders of magnitude. We observe a nonmonotonic behavior of the diffusion coefficient in dependence on the tumbling rate and identify a localization transition, either by increasing the density of obstacles or by decreasing the reorientation rate.
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Affiliation(s)
- Ehsan Irani
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), The Berlin Institute for Medical Systems Biology (BIMSB), 10115 Berlin, Germany
| | - Zahra Mokhtari
- Freie Universität Berlin, Department of Mathematics and Computer Science, Institute of Mathematics, Arnimallee 9, 14195 Berlin, Germany
| | - Annette Zippelius
- Georg-August-Universität Göttingen, Institut für Theoretische Physik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
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7
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Caprini L, Marini Bettolo Marconi U, Wittmann R, Löwen H. Dynamics of active particles with space-dependent swim velocity. SOFT MATTER 2022; 18:1412-1422. [PMID: 35080576 DOI: 10.1039/d1sm01648b] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
We study the dynamical properties of an active particle subject to a swimming speed explicitly depending on the particle position. The oscillating spatial profile of the swim velocity considered in this paper takes inspiration from experimental studies based on Janus particles whose speed can be modulated by an external source of light. We suggest and apply an appropriate model of an active Ornstein Uhlenbeck particle (AOUP) to the present case. This allows us to predict the stationary properties, by finding the exact solution of the steady-state probability distribution of particle position and velocity. From this, we obtain the spatial density profile and show that its form is consistent with the one found in the framework of other popular models. The reduced velocity distribution highlights the emergence of non-Gaussianity in our generalized AOUP model which becomes more evident as the spatial dependence of the velocity profile becomes more pronounced. Then, we focus on the time-dependent properties of the system. Velocity autocorrelation functions are studied in the steady-state combining numerical and analytical methods derived under suitable approximations. We observe a non-monotonic decay in the temporal shape of the velocity autocorrelation function which depends on the ratio between the persistence length and the spatial period of the swim velocity. In addition, we numerically and analytically study the mean square displacement and the long-time diffusion coefficient. The ballistic regime, observed in the small-time region, is deeply affected by the properties of the swim velocity landscape which induces also a crossover to a sub-ballistic but superdiffusive regime for intermediate times. Finally, the long-time diffusion coefficient decreases as the amplitude of the swim velocity oscillations increases because the diffusion is mainly determined by those regions where the particles are slow.
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Affiliation(s)
- Lorenzo Caprini
- Heinrich-Heine-Universität Düsseldorf, Institut für Theoretische Physik II - Soft Matter, D-40225 Düsseldorf, Germany
| | | | - René Wittmann
- Heinrich-Heine-Universität Düsseldorf, Institut für Theoretische Physik II - Soft Matter, D-40225 Düsseldorf, Germany
| | - Hartmut Löwen
- Heinrich-Heine-Universität Düsseldorf, Institut für Theoretische Physik II - Soft Matter, D-40225 Düsseldorf, Germany
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8
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Gerhard M, Jayaram A, Fischer A, Speck T. Hunting active Brownian particles: Learning optimal behavior. Phys Rev E 2021; 104:054614. [PMID: 34942812 DOI: 10.1103/physreve.104.054614] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Accepted: 11/16/2021] [Indexed: 01/02/2023]
Abstract
We numerically study active Brownian particles that can respond to environmental cues through a small set of actions (switching their motility and turning left or right with respect to some direction) which are motivated by recent experiments with colloidal self-propelled Janus particles. We employ reinforcement learning to find optimal mappings between the state of particles and these actions. Specifically, we first consider a predator-prey situation in which prey particles try to avoid a predator. Using as reward the squared distance from the predator, we discuss the merits of three state-action sets and show that turning away from the predator is the most successful strategy. We then remove the predator and employ as collective reward the local concentration of signaling molecules exuded by all particles and show that aligning with the concentration gradient leads to chemotactic collapse into a single cluster. Our results illustrate a promising route to obtain local interaction rules and design collective states in active matter.
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Affiliation(s)
- Marcel Gerhard
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany
| | - Ashreya Jayaram
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany
| | - Andreas Fischer
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany
| | - Thomas Speck
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany
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9
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Auschra S, Holubec V. Density and polarization of active Brownian particles in curved activity landscapes. Phys Rev E 2021; 103:062604. [PMID: 34271717 DOI: 10.1103/physreve.103.062604] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Accepted: 04/12/2021] [Indexed: 11/07/2022]
Abstract
Suspensions of motile active particles with space-dependent activity form characteristic polarization and density patterns. Recent single-particle studies for planar activity landscapes identified several quantities associated with emergent density-polarization patterns that are solely determined by bulk variables. Naive thermodynamic intuition suggests that these results might hold for arbitrary activity landscapes mediating bulk regions, and thus could be used as benchmarks for simulations and theories. However, the considered system operates in a nonequilibrium steady state and we prove by construction that the quantities in question lose their simple form for curved activity landscapes. Specifically, we provide a detailed analytical study of polarization and density profiles induced by radially symmetric activity steps, and of the total polarization for the case of a general radially symmetric activity landscape. While the qualitative picture is similar to the planar case, all the investigated variables depend not only on bulk variables but also comprise geometry-induced contributions. We verified that all our analytical results agree with exact numerical calculations.
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Affiliation(s)
- Sven Auschra
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Viktor Holubec
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany.,Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, CZ-180 00 Praha, Czech Republic
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10
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Auschra S, Bregulla A, Kroy K, Cichos F. Thermotaxis of Janus particles. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:90. [PMID: 34218345 PMCID: PMC8254728 DOI: 10.1140/epje/s10189-021-00090-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Accepted: 06/07/2021] [Indexed: 05/26/2023]
Abstract
The interactions of autonomous microswimmers play an important role for the formation of collective states of motile active matter. We study them in detail for the common microswimmer-design of two-faced Janus spheres with hemispheres made from different materials. Their chemical and physical surface properties may be tailored to fine-tune their mutual attractive, repulsive or aligning behavior. To investigate these effects systematically, we monitor the dynamics of a single gold-capped Janus particle in the external temperature field created by an optically heated metal nanoparticle. We quantify the orientation-dependent repulsion and alignment of the Janus particle and explain it in terms of a simple theoretical model for the induced thermoosmotic surface fluxes. The model reveals that the particle's angular velocity is solely determined by the temperature profile on the equator between the Janus particle's hemispheres and their phoretic mobility contrast. The distortion of the external temperature field by their heterogeneous heat conductivity is moreover shown to break the apparent symmetry of the problem.
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Affiliation(s)
- Sven Auschra
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Andreas Bregulla
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
| | - Klaus Kroy
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Frank Cichos
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
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11
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Söker NA, Auschra S, Holubec V, Kroy K, Cichos F. How Activity Landscapes Polarize Microswimmers without Alignment Forces. PHYSICAL REVIEW LETTERS 2021; 126:228001. [PMID: 34152174 DOI: 10.1103/physrevlett.126.228001] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Accepted: 04/20/2021] [Indexed: 06/13/2023]
Abstract
Active-particle suspensions exhibit distinct polarization-density patterns in activity landscapes, even without anisotropic particle interactions. Such polarization without alignment forces is at work in motility-induced phase separation and betrays intrinsic microscopic activity to mesoscale observers. Using stable long-term confinement of a single thermophoretic microswimmer in a dedicated force-free particle trap, we examine the polarized interfacial layer at a motility step and confirm that it does not exert pressure onto the bulk. Our observations are quantitatively explained by an analytical theory that can also guide the analysis of more complex geometries and many-body effects.
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Affiliation(s)
- Nicola Andreas Söker
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
| | - Sven Auschra
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Viktor Holubec
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
- Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, CZ-180 00 Prague, Czech Republic
| | - Klaus Kroy
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Frank Cichos
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
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12
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Auschra S, Holubec V, Söker NA, Cichos F, Kroy K. Polarization-density patterns of active particles in motility gradients. Phys Rev E 2021; 103:062601. [PMID: 34271745 DOI: 10.1103/physreve.103.062601] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2021] [Accepted: 04/21/2021] [Indexed: 11/07/2022]
Abstract
The colocalization of density modulations and particle polarization is a characteristic emergent feature of motile active matter in activity gradients. We employ the active-Brownian-particle model to derive precise analytical expressions for the density and polarization profiles of a single Janus-type swimmer in the vicinity of an abrupt activity step. Our analysis allows for an optional (but not necessary) orientation-dependent propulsion speed, as often employed in force-free particle steering. The results agree well with measurement data for a thermophoretic microswimmer presented in the companion paper [Söker et al., Phys. Rev. Lett. 126, 228001 (2021)10.1103/PhysRevLett.126.228001], and they can serve as a template for more complex applications, e.g., to motility-induced phase separation or studies of physical boundaries. The essential physics behind our formal results is robustly captured and elucidated by a schematic two-species "run-and-tumble" model.
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Affiliation(s)
- Sven Auschra
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
| | - Viktor Holubec
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany.,Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, CZ-180 00 Prague, Czech Republic
| | - Nicola Andreas Söker
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
| | - Frank Cichos
- Peter Debye Institute for Soft Matter Physics, Leipzig University, 04103 Leipzig, Germany
| | - Klaus Kroy
- Institute for Theoretical Physics, Leipzig University, 04103 Leipzig, Germany
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13
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Jose F, Anand SK, Singh SP. Phase separation of an active colloidal suspension via quorum-sensing. SOFT MATTER 2021; 17:3153-3161. [PMID: 33616149 DOI: 10.1039/d0sm02131h] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We present the Brownian dynamics simulation of an active colloidal suspension in two dimensions, where the self-propulsion speed of a colloid is regulated according to the local density sensed by it. The role of concentration-dependent motility in the phase-separation of colloids and their dynamics is investigated in detail. Interestingly, the system phase separates at a very low packing fraction (Φ≈ 0.125) at higher self-propulsion speeds (Pe), into a dense phase coexisting with a homogeneous phase and attains a long-range crystalline order beyond the transition point. The transition point is quantified here from the local density profiles and local and global-bond order parameters. We have shown that the characteristics of the phase diagram are qualitatively akin to the active Brownian particle (ABP) model. Moreover, our investigation reveals that the density-dependent motility amplifies the slow-down of the directed speed, which facilitates phase-separation even at low packing fractions. The effective diffusivity shows a crossover from quadratic rise to a power-law behavior of exponent 3/2 with Pe in the phase-separated regime. Furthermore, we have shown that the effective diffusion decreases exponentially with packing fraction in the phase-separated regime, while it shows a linear decrease in the single phase regime.
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Affiliation(s)
- Francis Jose
- Department of Physics, Indian Institute of Science Education and Research, Bhopal 462 066, Madhya Pradesh, India.
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14
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Schimansky-Geier L, Lindner B, Milster S, Neiman AB. Demixing of two species via reciprocally concentration-dependent diffusivity. Phys Rev E 2021; 103:022113. [PMID: 33736075 DOI: 10.1103/physreve.103.022113] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 01/22/2021] [Indexed: 11/07/2022]
Abstract
We propose a model for demixing of two species by assuming a density-dependent effective diffusion coefficient of the particles. Both sorts of microswimmers diffuse as active overdamped Brownian particles with a noise intensity that is determined by the surrounding density of the respective other species within a sensing radius r_{s}. A higher concentration of the first (second) sort will enlarge the diffusion and, in consequence, the intensity of the noise experienced by the second (first) sort. Numerical and analytical investigations of steady states of the macroscopic equations prove the demixing of particles due to this reciprocally concentration-dependent diffusivity. An ambiguity of the numerical integration scheme for the purely local model (r_{s}→0) is resolved by considering nonvanishing sensing radii in a nonlocal model with r_{s}>0.
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Affiliation(s)
- Lutz Schimansky-Geier
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany
| | - Benjamin Lindner
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany.,Bernstein Center for Computational Neuroscience Berlin, Philippstrasse 13, Haus 2, 10115 Berlin, Germany
| | - Sebastian Milster
- Institute of Physics, Humboldt University at Berlin, Newtonstrasse 15, D-12489 Berlin, Germany.,Institute of Physics, Albert Ludwig University of Freiburg Hermann-Herder-Strasse 3, D-79104 Freiburg, Germany
| | - Alexander B Neiman
- Department of Physics and Astronomy, Ohio University, Athens, Ohio 45701, USA.,Neuroscience Program, Ohio University, Athens, Ohio 45701, USA
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15
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Aguilar EJ, Barbosa VC, Donangelo R, Souza SR. Interspecies evolutionary dynamics mediated by public goods in bacterial quorum sensing. Phys Rev E 2021; 103:012403. [PMID: 33601496 DOI: 10.1103/physreve.103.012403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2020] [Accepted: 12/15/2020] [Indexed: 11/07/2022]
Abstract
Bacterial quorum sensing is the communication that takes place between bacteria as they secrete certain molecules into the intercellular medium that later get absorbed by the secreting cells themselves and by others. Depending on cell density, this uptake has the potential to alter gene expression and thereby affect global properties of the community. We consider the case of multiple bacterial species coexisting, referring to each one of them as a genotype and adopting the usual denomination of the molecules they collectively secrete as public goods. A crucial problem in this setting is characterizing the coevolution of genotypes as some of them secrete public goods (and pay the associated metabolic costs) while others do not but may nevertheless benefit from the available public goods. We introduce a network model to describe genotype interaction and evolution when genotype fitness depends on the production and uptake of public goods. The model comprises a random graph to summarize the possible evolutionary pathways the genotypes may take as they interact genetically with one another, and a system of coupled differential equations to characterize the behavior of genotype abundance in time. We study some simple variations of the model analytically and more complex variations computationally. Our results point to a simple trade-off affecting the long-term survival of those genotypes that do produce public goods. This trade-off involves, on the producer side, the impact of producing and that of absorbing the public good. On the nonproducer side, it involves the impact of absorbing the public good as well, now compounded by the molecular compatibility between the producer and the nonproducer. Depending on how these factors turn out, producers may or may not survive.
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Affiliation(s)
- Eduardo J Aguilar
- Instituto de Ciência e Tecnologia, Universidade Federal de Alfenas, Rodovia José Aurélio Vilela, 11999, 37715-400 Poços de Caldas, Minais Gerais, Brazil
| | - Valmir C Barbosa
- Programa de Engenharia de Sistemas e Computação, COPPE, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Sala H-319, 21941-914 Rio de Janeiro, Rio de Janeiro, Brazil
| | - Raul Donangelo
- Instituto de Física, Facultad de Ingeniería, Universidad de la República, Julio Herrera y Reissig 565, 11300 Montevideo, Uruguay
- Instituto de Física, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco A, 21941-909 Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sergio R Souza
- Instituto de Física, Universidade Federal do Rio de Janeiro, Centro de Tecnologia, Bloco A, 21941-909 Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Física, ICEx, Universidade Federal de Minas Gerais, Avenida Antônio Carlos, 6627, 31270-901 Belo Horizonte, Minais Gerais, Brazil
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16
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Abstract
Large-scale collective behavior in suspensions of active particles can be understood from the balance of statistical forces emerging beyond the direct microscopic particle interactions. Here we review some aspects of the collective forces that can arise in suspensions of self-propelled active Brownian particles: wall forces under confinement, interfacial forces, and forces on immersed bodies mediated by the suspension. Even for non-aligning active particles, these forces are intimately related to a non-uniform polarization of particle orientations induced by walls and bodies, or inhomogeneous density profiles. We conclude by pointing out future directions and promising areas for the application of collective forces in synthetic active matter, as well as their role in living active matter.
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Affiliation(s)
- Thomas Speck
- Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7-9, 55128 Mainz, Germany.
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