When are active Brownian particles and run-and-tumble particles equivalent? Consequences for motility-induced phase separation

By M. E. Cates, J. Tailleur. 2012

443 citations recorded by the source corpus.

Active Brownian particles (ABPs, such as self-phoretic colloids) swim at fixed speed v along a body-axis u that rotates by slow angular diffusion. Run-and-tumble particles (RTPs, such as motile bacteria) swim with constant u until a random tumble event suddenly decorrelates the orientation. We show that when the motility parameters depend on density ρ but not on u, the coarse-grained fluctuating hydrodynamics of interacting ABPs and RTPs can be mapped onto each other and are thus strictly equivalent. In both cases, a steeply enough decreasing v(ρ) causes phase separation in dimensions d = 2,3, even when no attractive forces act between the particles. This points to a generic role for motility-induced phase separation in active matter. However, we show that the ABP/RTP equivalence does not automatically extend to the more general case of u-dependent motilities.

Subfields: Biomedical Engineering, Condensed Matter Physics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/beb67bdc2f391724c2838935fd579b391f17c23e

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In Biomedical Engineering

In Condensed Matter Physics

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Citations in the corpus

The statistical physics of active matter: From self-catalytic colloids to living cells (2017, methodology): “Considering a self-propelled particle whose change in direction can occur due to both instantaneous reorientation and angular diffusion, the correlations of self-propulsion are given by (6) with τ−1 = ν + (d − 1)Dr [27]: this is the relation between the persistence of the self-propulsion fluctuation”
Minimal model of active colloids highlights the role of mechanical interactions in controlling the emergent behavior of active matter (2015, methodology): “the density-dependent propulsion speed v(ρ) that controls the swim pressure [43, 22, 45, 41, 40], and then employ linear stability analysis to locate the spinodal.”
Entropy production in field theories without time reversal symmetry: Quantifying the non-equilibrium character of active matter (2016, background): “It captures in stylized form the coarse-grained many-body dynamics of active particles with either discrete [10, 21] or continuous [54, 55] angular relaxation of their self-propulsion direction.”
Physics of microswimmers—single particle motion and collective behavior: a review (2014, result): “Moreover, these studies support the argument that hydrodynamic effects contribute to the observed long residence times of bacteria close to no-slip surfaces (Berke et al 2008). In contrast, the experiments of Drescher et al (2011) suggest that cell-surface collisions determine the cell behavior next”
Tuned, driven, and active soft matter (2015, background): “g mechanism was analyzed in more detail [411] and also investigated experimentally [361]. A real phase separation into a clustered and a gas-like phase can be obtained as a steady state of the system [410, 413, 463]. For clarity, it is stressed that these clusters form in the absence of any 3This wa”
Pressure is not a state function for generic active fluids (2014, background): “2, the flux-free steady state has ρ ∝ 1/v throughout [25, 26, 35], so that the pressures P1,2 ∝ ρv2 are unequal.”