Morphology of clusters of attractive dry and wet self-propelled spherical particle suspensions

Alarcón, Francisco; Valeriani, Chantal; Pagonabarraga, Ignacio

doi:10.1039/c6sm01752e

Cited by 58 publications

(78 citation statements)

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“…In addition, recent simulations have shown that clusters are absent in 2D squirmer suspensions and in a 2D squirmer monolayer embedded in a 3D fluid [27,34]. While attractive interactions can lead to clustering [35][36][37], here we study swimmers with purely repulsive interactions to see role of hydrodynamics in active cluster formation.It is accepted from continuum arguments that the polar state is generically unstable for wet active systems [1][2][3], however recent simulations of wet active particles have raised the interesting possibility of other continuum limits in these systems. A polar state has been observed for neutral squirmers with no force dipole with 3D hydrodynamics, but 2D motion [19] and in 3D [38][39][40].…”

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Hydrodynamic interactions in dense active suspensions: From polar order to dynamical clusters

Yoshinaga

Liverpool

2017

Phys. Rev. E

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We study the role of hydrodynamic interactions in the collective behaviour of collections of microscopic active particles suspended in a fluid. We introduce a novel calculational framework that allows us to separate the different contributions to their collective dynamics from hydrodynamic interactions on different length scales. Hence we are able to systematically show that lubrication forces when the particles are very close to each other play as important a role as long-range hydrodynamic interactions in determining their many-body behaviour. We find that motility-induced phase separation is suppressed by near-field interactions, leading to open gel-like clusters rather than dense clusters. Interestingly, we find a globally polar ordered phase appears for neutral swimmers with no force dipole that is enhanced by near field lubrication forces in which the collision process rather than long-range interaction dominates the alignment mechanism.PACS numbers: 87.18. Hf,64.75.Xc, Active materials are condensed matter systems selfdriven out of equilibrium by components that convert stored energy into movement. They have generated much interest recently, both as inspiration for new smart materials and as a framework to understand aspects of cell motility [1][2][3]. They are characterised by interesting nonequilibrium collective phenomena, such as swirling, alignment, pattern formation, dynamic cluster formation and phase separation [4][5][6][7][8]. Theoretical descriptions of active systems range from continuum models [1, 9] to discrete collections of self-propelled active particles [4]. An influential classification of self-propelled active particle systems has been to group them into dry and wet systems [1]. Dry systems do not have momentum conserving dynamics (e.g, Vicsek models [4, 9] and Active Brownian particle (ABP) models interacting via soft repulsive potentials [10][11][12]), while wet systems conserve momentum via a coupling to a fluid (e.g. Squirmers driven by surface deformations [13][14][15] and Janus particles driven by surface chemical reactions [16]) leading to hydrodynamic interactions between active particles. Dealing with hydrodynamics leads to significant technical hurdles; as the motion of a self-propelled swimmer is affected by other particles due to both fluid flow and pressure, and even the two-body interaction between spherical squirmers in close proximity (near-field) is non-trivial, requiring sophisticated numerical analyses [17][18][19][20][21][22][23]. Therefore, converting this into an understanding of collective behaviour remains a significant challenge [24]. Because numerical simulations with hydrodynamics require significantly more computational power, studies of these systems have * E-mail: yoshinaga@tohoku.ac.jp † E-mail: t.liverpool@bristol.ac.uk relatively few particles or low resolution of fluid flow [25][26][27][28]. Hence, far-field approximations (swimmers as point multipoles ) [29] are often used to account for hydrodynamic interactions [30]. This clearly breaks down when the...

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Hydrodynamic interactions in dense active suspensions: From polar order to dynamical clusters

Yoshinaga

Liverpool

2017

Phys. Rev. E

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“…Our findings should complement more detailed work that could connect our activity channels to microscopic interactions [6][7][8][9][10]. They may also be be relevant to continuum models of multiple species (some non-conserved [30]) that were used recently to study microphase separations used by cells to create cytoplasmic and nucleoplasmic organization [31,32].…”

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confidence: 53%

“…A generic understanding of such nonequilibrium microphase separations can be sought at the level of continuum equations for a diffusive scalar concentration field, coupled to incompressible fluid flow. Such an approach is complementary to more detailed mechanistic modelling, in which particle motion and/or chemical fields are modelled explicitly [6][7][8][9][10]. By sacrificing detail, the resulting 'active field theory' allows maximal transfer of ideas and methods from equilibrium statistical mechanics.…”

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Hydrodynamically Interrupted Droplet Growth in Scalar Active Matter

Singh

Cates

2019

Phys. Rev. Lett.

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Suspensions of spherical active particles often show microphase separation. At a continuum level, coupling their scalar density to fluid flow, there are two distinct explanations. Each involves an effective interfacial tension: the first mechanical (causing flow) and the second diffusive (causing Ostwald ripening). Here we show how the negative mechanical tension of contractile swimmers creates, via a self-shearing instability, a steady-state life cycle of droplet growth interrupted by division whose scaling behavior we predict. When the diffusive tension is also negative, this is replaced by an arrested regime (mechanistically distinct, but with similar scaling) where division of small droplets is prevented by reverse Ostwald ripening.

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“…As in Ref. [26], we quantify the competition between attractive and self-propelling forces via the dimensionless parameter…”

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Orientational order and morphology of clusters of self-assembled Janus swimmers

et al. 2019

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Due to the combined effect of anisotropic interactions and activity, Janus swimmers are capable to self-assemble in a wide variety of structures, many more than their equilibrium counterpart. This might lead to the development of novel active materials capable of performing tasks without any central control. Their potential application in designing such materials endows trying to understand the fundamental mechanism in which these swimmers self-assemble. In the present work, we study a quasi-two dimensional semi-dilute suspensions of two classes of amphiphilic spherical swimmers whose direction of motion can be tuned: either swimmers propelling in the direction of the hydrophobic patch (WP), or swimmers propelling in the opposite direction (towards the hydrophilic side) (AP). In both systems we have systematically tuned swimmers' hydrophobic strength and signature, and observed that the anisotropic interactions, characterized by the angular attractive potential and its interaction range, in competition with the active stress, pointing towards or against the attractive patch gives rise to a rich aggregation phenomenology. arXiv:1905.08541v1 [cond-mat.soft]

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Morphology of clusters of attractive dry and wet self-propelled spherical particle suspensions

Cited by 58 publications

References 63 publications

Hydrodynamic interactions in dense active suspensions: From polar order to dynamical clusters

Hydrodynamic interactions in dense active suspensions: From polar order to dynamical clusters

Hydrodynamically Interrupted Droplet Growth in Scalar Active Matter

Orientational order and morphology of clusters of self-assembled Janus swimmers

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