Demixing of active particles in the presence of external fields

Kumari, Sunita; Nunes, André S.; Araújo, Nuno A. M.; Gama, Margarida Telo da

doi:10.1063/1.4992797

Cited by 18 publications

(9 citation statements)

References 41 publications

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“…The most intriguing feature of such multicomponent active systems is their capability to demix, which cannot be attributed to the physical mechanisms also present in equilibrium mixtures. Some recent investigations have focused on such a binary mixture of an active and a passive species [24][25][26] or particles with different finite activities [26][27][28][29]. Quite intuitively, active phase separation phenomena can be described using the concept of an effective temperature, enhanced by activity [30], which has also been applied to mixtures [27,31,32].…”

Section: Introductionmentioning

confidence: 99%

Effective equilibrium states in mixtures of active particles driven by colored noise

et al. 2018

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We consider the steady-state behavior of pairs of active particles having different persistence times and diffusivities. To this purpose we employ the active Ornstein-Uhlenbeck model, where the particles are driven by colored noises with exponential correlation functions whose intensities and correlation times vary from species to species. By extending Fox's theory to many components, we derive by functional calculus an approximate Fokker-Planck equation for the configurational distribution function of the system. After illustrating the predicted distribution in the solvable case of two particles interacting via a harmonic potential, we consider systems of particles repelling through inverse power-law potentials. We compare the analytic predictions to computer simulations for such soft-repulsive interactions in one dimension and show that at linear order in the persistence times the theory is satisfactory. This work provides the toolbox to qualitatively describe many-body phenomena, such as demixing and depletion, by means of effective pair potentials.

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Section: Introductionmentioning

confidence: 99%

Effective equilibrium states in mixtures of active particles driven by colored noise

et al. 2018

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“…In particular, different kinds of active particles (see Refs. [87][88][89][90] for recent studies) can be separated and sorted. This is of particular importance since an inhomogeneous motility field (e.g.…”

Section: Discussionmentioning

confidence: 99%

Colloidal Brazil nut effect in microswimmer mixtures induced by motility contrast

Jahanshahi

Lozano

Hagen

et al. 2019

The Journal of Chemical Physics

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We numerically and experimentally study the segregation dynamics in a binary mixture of microswimmers which move on a two-dimensional substrate in a static periodic triangular-like light intensity field. The motility of the active particles is proportional to the imposed light intensity and they possess a motility contrast, i.e., the prefactor depends on the species. In addition, the active particles also experience a torque aligning their motion towards the direction of the negative intensity gradient. We find a segregation of active particles near the intensity minima where typically one species is localized close to the minimum and the other one is centered around in an outer shell. For a very strong aligning torque, there is an exact mapping onto an equilibrium system in an effective external potential that is minimal at the intensity minima. This external potential is similar to (height-dependent) gravity, such that one can define effective "heaviness" of the self-propelled particles. In analogy to shaken granular matter in gravity, we define a "colloidal Brazil nut effect" if the heavier particles are floating on top of the lighter ones. Using extensive Brownian dynamics simulations, we identify system parameters for the active colloidal Brazil nut effect to occur and explain it based on a generalized Archimedes' principle within the effective equilibrium model: heavy particles are levitated in a dense fluid of lighter particles if their effective mass density is lower than that of the surrounding fluid. We also perform real-space experiments on light-activated self-propelled colloidal mixtures which confirm the theoretical predictions. arXiv:1901.10201v1 [cond-mat.soft]

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“…These studies have inspired a larger number of investigations on phase separation in suspensions of self-moving object. Various interesting problems have been put forward as for example, the mixtures of active and passive or fast and slow particles [18][19][20][21][22][23][24], the influences of different speeds of phase separation [25], different diffusivities [26], a discontinuous motility [27,28], demixing of active particles in external fields [29], chiral active matter [30], descriptions of phase separation far from equilibrium in continuum frame [31], learning of groups in swarms [32] and chemotactically reacting particles [33,34], to mention just a few publications. Also early work on chemically reacting active Brownian particles creating complex behavior during trail formation of ants and in excitable dynamics deserves to be mentioned [35,36].…”

Section: Introductionmentioning

confidence: 99%

Demixing of two species via reciprocally concentration-dependent diffusivity

Schimansky-Geier,

Lindner,

Milster

et al. 2020

Preprint

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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 rs. 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 (rs → 0) is resolved by considering nonvanishing sensing radii in a nonlocal model with rs > 0.

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Demixing of active particles in the presence of external fields

Cited by 18 publications

References 41 publications

Effective equilibrium states in mixtures of active particles driven by colored noise

Effective equilibrium states in mixtures of active particles driven by colored noise

Colloidal Brazil nut effect in microswimmer mixtures induced by motility contrast

Demixing of two species via reciprocally concentration-dependent diffusivity

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