Spreading dynamics of reactive surfactants driven by Marangoni convection

Bickel, Thomas

doi:10.1039/c8sm02641f

Cited by 25 publications

(29 citation statements)

References 47 publications

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“…Note that Refs. [80,81] suggest that in some situations the outcome of Marangoni flows is to renormalize the effective diffusivity of the surfactant. If applicable in our system, then such an equivalence would offer a very simple path to account for Marangoni effects within the point-source framework.…”

Section: Discussionmentioning

confidence: 99%

Self-propulsion of symmetric chemically active particles: Point-source model and experiments on camphor disks

et al. 2019

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Solid undeformable particles surrounded by a liquid medium or interface may propel themselves by altering their local environment. Such nonmechanical swimming is at work in autophoretic swimmers, whose selfgenerated field gradient induces a slip velocity on their surface, and in interfacial swimmers, which exploit unbalance in surface tension. In both classes of systems, swimmers with intrinsic asymmetry have received the most attention but self-propulsion is also possible for particles that are perfectly isotropic. The underlying symmetry-breaking instability has been established theoretically for autophoretic systems but has yet to be observed experimentally for solid particles. For interfacial swimmers, several experimental works point to such a mechanism, but its understanding has remained incomplete. The goal of this work is to fill this gap. Building on an earlier proposal, we first develop a point-source model that may be applied generically to interfacial or phoretic swimmers. Using this approximate but unifying picture, we show that they operate in very different regimes and obtain analytical predictions for the propulsion velocity and its dependence on swimmer size and asymmetry. Next, we present experiments on interfacial camphor disks showing that they indeed self-propel in an advection-dominated regime where intrinsic asymmetry is irrelevant and that the swimming velocity increases sublinearly with size. Finally, we discuss the merits and limitations of the point-source model in light of the experiments and point out its broader relevance.

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Section: Discussionmentioning

confidence: 99%

Self-propulsion of symmetric chemically active particles: Point-source model and experiments on camphor disks

et al. 2019

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“…In such models, the Newtonian equation describes object motion and a reaction-diffusion equation with an effective value of diffusion constant, that incorporates advection, represents the time evolution of camphor surface concentration. Such a model has been successfully used for qualitative explanation of many experimental results [39][40][41] . However, it cannot be applied for the case when the object motion is externally perturbed and the flow evolution is not determined by location of objects and by camphor surface concentration.…”

Section: Discussionmentioning

confidence: 99%

“…As mentioned above, the simple model of evolution for camphor-propelled objects, that treats Marangoni flows by an effective diffusion constant, can qualitatively describe many observed phenomena [39][40][41] . However, this model is not applicable to the inversion of rotational direction under stop-and-release operations, because it does not treat separately the evolution of flows and the camphor surface concentration.…”

Section: Introductionmentioning

confidence: 99%

On a simple model that explains inversion of a self-propelled rotor under periodic stop-and-release-operations

Koyano

Kitahata

Nakata

et al. 2020

Chaos: An Interdisciplinary Journal of Nonlinear Science

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We propose a simple mathematical model that describes the time evolution of a self-propelled object on a liquid surface using such variables as the object location, the surface concentration of active molecules and the hydrodynamic surface flow. The model is applied to simulate the time evolution of a rotor composed of a polygonal plate with camphor pills at its corners. We have qualitatively reproduced results of experiments, in which the inversion of rotational direction under periodic stop-and-release operations was investigated. The model correctly describes the probability of the inversion as a function of the duration of the phase when the rotor is stopped. Moreover, the model allows to introduce the rotor asymmetry unavoidable in real experiments and study its influence on the studied phenomenon. Our numerical simulations have revealed that the probability of the inversion of rotational direction is determined by the competition among the transport of the camphor molecules by the flow, the intrinsic asymmetry of the rotor, and the noise amplitude.

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“…First, we restrict the discussion to the stationary regime. Although time-dependent behaviors might be relevant, regarding for instance the relaxation dynamics when the source is swiched on or off [30], they are not considered here. We also focus on radially symmetric sources and set r = (r, z), with r = x 2 + y 2 .…”

Section: Simplifying Assumptionsmentioning

confidence: 99%

Effect of surface-active contaminants on radial thermocapillary flows

Bickel

2019

Eur. Phys. J. E

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We study the thermocapillary creeping flow induced by a thermal gradient at the liquid-air interface in the presence of insoluble surfactants (impurities). Convective sweeping of the surfactants causes density inhomogeneities that confers in-plane elastic features to the interface. This mechanism is discussed for radially symmetric temperature fields, in both the deep and shallow water regimes. When mass transport is controlled by convection, it is found that surfactants are depleted from a region whose size is inversely proportional to the interfacial elasticity. Both the concentration and the velocity fields follow power laws at the border of the depleted region. Finally, it is shown that this singular behavior is smeared out when molecular diffusion is accounted for.

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Spreading dynamics of reactive surfactants driven by Marangoni convection

Cited by 25 publications

References 47 publications

Self-propulsion of symmetric chemically active particles: Point-source model and experiments on camphor disks

Self-propulsion of symmetric chemically active particles: Point-source model and experiments on camphor disks

On a simple model that explains inversion of a self-propelled rotor under periodic stop-and-release-operations

Effect of surface-active contaminants on radial thermocapillary flows

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