Dynamics of self-propelled nanomotors in chemically active media

Thakur, Snigdha; Kapral, Raymond

doi:10.1063/1.3607408

Cited by 53 publications

(67 citation statements)

References 53 publications

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“…A number of different systems, employing this propulsive mechanism on the micro-and nanometer scale, have been suggested [1][2][3][4][5][6][7][8] . They open exiting, possible routes for future engineering of nano-devices [9][10][11][12][13][14][15] .…”

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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“…Other mechanisms are, e.g., oxidation and reduction of glucose 11 , hydrolyzation 12 or bromination 13 at droplet surfaces, and thermally induced phase separation around a swimmer 14 . Finally, a number of theoretical studies have been conducted with generic chemical reaction schemes [15][16][17] . In previous theoretical work 18,19 we have investigated the efficiency of this surface-driven propulsion since its exciting potential for use with micromachines has been amply demonstrated [20][21][22][23] .…”

Section: Introductionmentioning

confidence: 99%

Nonlinear, electrocatalytic swimming in the presence of salt

Sabass

Seifert

2012

The Journal of Chemical Physics

112

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A small, bimetallic particle in a hydrogen peroxide solution can propel itself by means of an electrocatalytic reaction. The swimming is driven by a flux of ions around the particle. We model this process for the presence of a monovalent salt, where reaction-driven proton currents induce salt ion currents. A theory for thin diffuse layers is employed, which yields nonlinear, coupled transport equations. The boundary conditions include a compact Stern layer of adsorbed ions. Electrochemical processes on the particle surface are modeled with a first order reaction of the Butler-Volmer type. The equations are solved numerically for the swimming speed. An analytical approximation is derived under the assumption that the decomposition of hydrogen peroxide occurs mainly without inducing an electric current. We find that the swimming speed increases linearly with hydrogen peroxide concentration for small concentrations. The influence of ion diffusion on the reaction rate can lead to a concave shape of the function of speed vs. hydrogen peroxide concentration. The compact layer of ions on the particle diminishes the reaction rate and consequently reduces the speed. Our results are consistent with published experimental data.

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“…Numerous physical models of interacting self-propelled agents have been proposed recently to study these phenomena (see review papers [1][2][3]). The collective behavior much resembling the dynamics of living organisms has also been observed in a variety of synthetic systems, generally referred to as active soft matter [4][5][6][7][8][9][10]. The level of consciousness of the individuals apparently plays minor role for the large scale dynamics as the same general principles that apply to groups of animals or cells seem to govern also human social phenomena, traffic, robotics, and decision making [11][12][13][14].…”

Section: Introductionmentioning

confidence: 95%

Tricritical points in a Vicsek model of self-propelled particles with bounded confidence

2014

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We study the orientational ordering in systems of self-propelled particles with selective interactions. To introduce the selectivity we augment the standard Vicsek model with a bounded-confidence collision rule: a given particle only aligns to neighbors who have directions quite similar to its own. Neighbors whose directions deviate more than a fixed restriction angle α are ignored. The collective dynamics of this systems is studied by agent-based simulations and kinetic mean field theory. We demonstrate that the reduction of the restriction angle leads to a critical noise amplitude decreasing monotonically with that angle, turning into a power law with exponent 3/2 for small angles. Moreover, for small system sizes we show that upon decreasing the restriction angle, the kind of the transition to polar collective motion changes from continuous to discontinuous. Thus, an apparent tricritical point with different scaling laws is identified and calculated analytically. We investigate the shifting and vanishing of this point due to the formation of density bands as the system size is increased. Agent-based simulations in small systems with large particle velocities show excellent agreement with the kinetic theory predictions. We also find that at very small interaction angles the polar ordered phase becomes unstable with respect to the apolar phase. We derive analytical expressions for the dependence of the threshold noise on the restriction angle. We show that the mean-field kinetic theory also permits stationary nematic states below a restriction angle of 0.681 π. We calculate the critical noise, at which the disordered state bifurcates to a nematic state, and find that it is always smaller than the threshold noise for the transition from disorder to polar order. The disordered-nematic transition features two tricritical points: At low and high restriction angle the transition is discontinuous but continuous at intermediate α. We generalize our results to systems that show fragmentation into more than two groups and obtain scaling laws for the transition lines and the corresponding tricritical points. A novel numerical method to evaluate the nonlinear Fredholm integral equation for the stationary distribution function is also presented. This method is shown to give excellent agreement with agent-based simulations, even in strongly ordered systems at noise values close to zero.

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Dynamics of self-propelled nanomotors in chemically active media

Cited by 53 publications

References 53 publications

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Dynamics and efficiency of a self-propelled, diffusiophoretic swimmer

Nonlinear, electrocatalytic swimming in the presence of salt

Tricritical points in a Vicsek model of self-propelled particles with bounded confidence

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