Active Colloidal Suspensions Exhibit Polar Order under Gravity

Enculescu, Mihaela; Stark, Holger

doi:10.1103/physrevlett.107.058301

Cited by 166 publications

(251 citation statements)

References 35 publications

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“…Furthermore, self-propelled small swimmers provide a unique chance to study artificial motion at the nanometer scale, e.g., to investigate anomalous diffusion [16][17][18] or non equilibrium thermodynamics 19,20 . Other interesting questions relating to mutual interactions of these swimmers and interactions with the environment are also beginning to be addressed [21][22][23][24] . In most of these experiments, a catalytic decomposition of hydrogen peroxide H 2 O 2 into oxygen O 2 (g) and water is employed for propulsion.…”

Section: Introductionmentioning

confidence: 99%

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Sabass

Seifert

2012

The Journal of Chemical Physics

106

136

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Active diffusiophoresis -swimming through interaction with a self-generated, neutral, solute gradient -is a paradigm for autonomous motion at the micrometer scale. We study this propulsion mechanism within a linear response theory. Firstly, we consider several aspects relating to the dynamics of the swimming particle. We extend established analytical formulae to describe small swimmers, which interact with their environment on a finite lengthscale. Solute convection is also taken into account. Modeling of the chemical reaction reveals a coupling between the angular distribution of reactivity on the swimmer and the concentration field. This effect, which we term "reaction induced concentration distortion", strongly influences the particle speed. Building on these insights, we employ irreversible, linear thermodynamics to formulate an energy balance. This approach highlights the importance of solute convection for a consistent treatment of the energetics. The efficiency of swimming is calculated numerically and approximated analytically. Finally, we define an efficiency of transport for swimmers which are moving in random directions. It is shown that this efficiency scales as the inverse of the macroscopic distance over which transport is to occur.

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Section: Introductionmentioning

confidence: 99%

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Sabass

Seifert

2012

The Journal of Chemical Physics

106

136

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“…In order to understand the collective dynamics of active particles and their steady-state distributions, they are often mapped onto passive systems that move in effective potentials [24][25][26]. However, for interacting particles there is no general route for identifying an equilibrium counterpart [1,6,10].…”

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confidence: 99%

Self-Induced Polar Order of Active Brownian Particles in a Harmonic Trap

2014

Self Cite

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Hydrodynamically interacting active particles in an external harmonic potential form a selfassembled fluid pump at large enough Péclet numbers. Here, we give a quantitative criterion for the formation of the pump and show that particle orientations align in the self-induced flow field in surprising analogy to ferromagnetic order where the active Péclet number plays the role of inverse temperature. The particle orientations follow a Boltzmann distribution Φ(p) ∼ exp(Apz) where the ordering mean field A scales with active Péclet number and polar order parameter. The mean flow field in which the particles' swimming directions align corresponds to a regularized stokeslet with strength proportional to swimming speed. Analytic mean-field results are compared with results from Brownian dynamics simulations with hydrodynamic interactions included and are found to capture the self-induced alignment very well.Introduction Understanding the non-equilibrium behavior of self-propelled particles is one of the major challenges at the interface of physics, biology, and also chemical engineering [1,2]. Interacting active particles may show exotic phenomena such as swirling motion In order to understand the collective dynamics of active particles and their steady-state distributions, they are often mapped onto passive systems that move in effective potentials [24][25][26]. However, for interacting particles there is no general route for identifying an equilibrium counterpart [1,6,10].The system we investigate here is composed of selfpropelled or active Brownian particles whose swimming directions undergo rotational diffusion in a harmonic trap. Bacteria or both active and passive colloids confined in optical traps have attracted experimental [27][28][29] as well as theoretical [24,[30][31][32][33] interest. Passive colloids are operated in non-equilibrium by switching the trapping force [31] while active particles are intrinsically out of equilibrium [24,32,33]. Run-and-tumble particles in lattice Boltzmann simulations develop a pump state which breaks the rotational symmetry of the harmonic trap and cause a macroscopic fluid flow [32]. Here, we demonstrate similar behavior for active Brownian particles which interact by hydrodynamic flow fields. However, more importantly we explain the emerging orientational order of particles by mapping the self-induced alignment of swimmers in a harmonic potential onto an equilibrium system which exhibits ferromagnetic order.To this end we first establish a quantitative criterion for the formation of the pump and then introduce a mean-field description for the fully formed pump state. The mean-field system shows a striking analogy to the

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“…However, active matters in biological and physical systems have been studied theoretically and experimentally [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. The kinetics of active particles moving in periodic structures could exhibit peculiar behaviors.…”

Section: Introductionmentioning

confidence: 99%

Entropic Ratchet transport of interacting active Brownian particles

Zhong

2014

The Journal of Chemical Physics

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Directed transport of interacting active (self-propelled)Brownian particles is numerically investigated in confined geometries (entropic barriers). The self-propelled velocity can break thermodynamical equilibrium and induce the directed transport. It is found that the interaction between active particles can greatly affect the ratchet transport. For attractive particles, on increasing the interaction strength, the average velocity firstly decreases to its minima, then increases, and finally decreases to zero. For repulsive particles, when the interaction is very weak, there exists a critical interaction at which the average velocity is minimal, nearly tends to zero, however, for the strong interaction, the average velocity is independent of the interaction.

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Active Colloidal Suspensions Exhibit Polar Order under Gravity

Cited by 166 publications

References 35 publications

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Self-Induced Polar Order of Active Brownian Particles in a Harmonic Trap

Entropic Ratchet transport of interacting active Brownian particles

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