Alignment and scattering of colliding active droplets

Lippera, Kevin; Benzaquen, Michael; Michelin, Sébastien

doi:10.1039/d0sm01285h

Cited by 24 publications

(25 citation statements)

References 40 publications

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“…Recent advances have, however, been obtained for a closely connected case: active droplets embedded in a three-dimensional (3D) liquid phase that also exhibit swimming by spontaneous symmetry breaking. In this system, which proved more amenable to analytical development of the full problem than surfers, the properties of 2D binary interactions were recently addressed [44][45][46]. The collision data reported for these active droplets are in agreement with experimental investigations [47,48], and display properties very similar to those presented here.…”

Section: Two-body Interactionsupporting

confidence: 78%

Two-dimensional numerical model of Marangoni surfers: From single swimmer to crystallization

et al. 2021

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We numerically study the dynamics of an ensemble of Marangoni surfers in a two-dimensional and unconfined space. The swimmers are modeled as Gaussian sources of surfactant generating surface tension gradients and are shown to follow the Marangoni flow filtered at their spatial scale in the lubrication regime, an unstable situation leading to spontaneous motion as soon as the Marangoni effect is intense enough. As the system is fully unconstrained, it is possible to study the various dynamical regimes from single swimmer, two-body interaction, to the many-particles case characterized by an efficient particle dispersion. We show that, although the present model is very simple, it reproduces the experimentally observed transition between a regime of dispersion by random agitation when the number of swimmers is moderate to the regime of crystallization with imperfect hexagonal lattice at high density.

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Section: Two-body Interactionsupporting

confidence: 78%

Two-dimensional numerical model of Marangoni surfers: From single swimmer to crystallization

et al. 2021

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“…We note that axisymmetric (Lippera et al. 2020 c ; Lippera, Benzaquen & Michelin 2020 b ) and planar (Lippera, Benzaquen & Michelin 2020 a ) interactions have recently been considered in the different physical context of active droplets, discussed in § 1. These studies also employed a weakly nonlinear analysis near the critical Péclet number (Lippera et al.…”

Section: Discussionmentioning

confidence: 99%

“…Rather than external forcing, one could also consider perturbations owing to a slight asymmetry in the particle geometry or surface composition, or weak interactions with distant particles and boundaries. We note that axisymmetric (Lippera et al 2020c;Lippera, Benzaquen & Michelin 2020b) and planar (Lippera, Benzaquen & Michelin 2020a) interactions have recently been considered in the different physical context of active droplets, discussed in § 1. These studies also employed a weakly nonlinear analysis near the critical Péclet number (Lippera et al 2020c).…”

Section: Discussionmentioning

confidence: 99%

Isotropically active colloids under uniform force fields: from forced to spontaneous motion

2021

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“…Given the numerical demand and difficulty of a complete description, the only route to address such phenomena is to design simplified models for swimmers. We believe point source models discussed here remain useful approaches for guiding the exploration of more complex situations [107] with the present work delimiting their capabilities and helping for further improvements. lead eventually to…”

Section: Discussionmentioning

confidence: 94%

Role of Marangoni forces in the velocity of symmetric interfacial swimmers

et al. 2021

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Interfacial swimmers are objects that self-propel at an interface by autonomously generating a gradient of surface tension, often through the continuous release of a surfactant. While the case of asymmetric swimmers has long been studied, experiments have shown that spontaneous motion is also possible for symmetric swimmers. The basic mechanism of symmetry-breaking is qualitatively well-established but one key aspect of the phenomenon that has proved particularly difficult to elucidate is the role of Marangoni effects in the self-propulsion. We address this question by numerical methods, which can fully handle the complex interplay between swimmer motion, fluid flow, surfactant distribution, and Marangoni stresses. Our swimmer is a disk releasing a soluble surfactant in a deep-layer fluid. We investigate how the swimming velocity, represented by a Péclet number Pe * depends on its characteristics, as encapsulated in the Marangoni number M. We analyze the properties of the swimming diagram Pe * (M) and compare with approximate models to understand their origin. We find that the low-Pe * regime exhibits a bistability region: spontaneous swimming involves a threshold Marangoni number, a discontinuity in velocity and possibly hysteresis. Those features are present only for a full description of the problem and reveal the subtle but key role of Marangoni flows. The large-Pe * regime features a robust asymptotic scaling law Pe * ∼ M α , whose exponent α 0.72 is close to the 3/4 value predicted by a simplified model, indicating a much weaker influence of Marangoni flows. While our results were obtained assuming a point-source swimmer in the Stokes flow regime, we show that the picture remains very similar when considering a spatially extended source size, finite Reynolds number, or a fixed concentration swimmer. We discuss our findings in relation to experiments.

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Alignment and scattering of colliding active droplets

Abstract: While direct collisions of two chemically-active droplets promote their alignment, interactions via their chemical wake can result in a significant scattering.

Cited by 24 publications

References 40 publications

Two-dimensional numerical model of Marangoni surfers: From single swimmer to crystallization

Two-dimensional numerical model of Marangoni surfers: From single swimmer to crystallization

Isotropically active colloids under uniform force fields: from forced to spontaneous motion

Role of Marangoni forces in the velocity of symmetric interfacial swimmers

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