Nonlinear dynamics of a chemically-active drop: From steady to chaotic self-propulsion

Morozov, Matvey; Michelin, Sébastien

doi:10.1063/1.5080539

Cited by 72 publications

(205 citation statements)

References 30 publications

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“…in refs. [71,72] the movement of a charged oil droplet in a solute gradient is referred to as diffusiophoresis, as then a discontinuity in the flow velocity across the droplet interface arises, while the hydrodynamic stresses at the interface are continuous, see figure 1 of ref. [72].…”

Section: Immiscible Droplet In a Concentration Gradientmentioning

confidence: 99%

Physicochemical hydrodynamics of droplets out of equilibrium

2020

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Droplets abound in nature and technology. In general, they are multicomponent, and, when out of equilibrium, with gradients in concentration, implying flow and mass transport. Moreover, phase transitions can occur, with either evaporation, solidification, dissolution, or nucleation of a new phase. The droplets and their surrounding liquid can be binary, ternary, or contain even more components, and with several even in different phases. In the last two decades the rapid advances in experimental and numerical fluid dynamical techniques has enabled major progress in our understanding of the physicochemical hydrodynamics of such droplets, further narrowing the gap from fluid dynamics to chemical engineering and colloid & interfacial science and arriving at a quantitative understanding of multicomponent and multiphase droplet systems far from equilibrium, and aiming towards a one-to-one comparison between experiments and theory or numerics. This review will discuss various examples of the physicochemical hydrodynamics of droplet systems far from equilibrium and our present understanding of them. These include immiscible droplets in a concentration gradient, coalescence of droplets of different liquids, droplets in concentration gradients emerging from chemical reactions (including droplets as microswimmers) and phase transitions such as evaporation, solidification, dissolution, or nucleation, and droplets in ternary liquids, including solvent exchange, nano-precipitation, and the so-called ouzo effect. We will also discuss the relevance of the physicochemical hydrodynamics of such droplet systems for many important applications, including in chemical analysis and diagnostics, microanalysis, pharmaceutics, synthetic chemistry and biology, chemical and environmental engineering, the oil and remediation industries, inkjet-printing, for micro-and nano-materials, and in nanotechnolgoy.

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Section: Immiscible Droplet In a Concentration Gradientmentioning

confidence: 99%

Physicochemical hydrodynamics of droplets out of equilibrium

2020

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“…As a result, general solutions for N (2) i , and F (2) i may be adapted directly from Refs. [38,40],…”

Section: B Problem At 2 : Droplet Interactionmentioning

confidence: 99%

Collisions and rebounds of chemically active droplets

et al. 2020

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Active droplets swim as a result of the nonlinear advective coupling of the distribution of chemical species they consume or release with the Marangoni flows created by their non-uniform surface distribution. Most existing models focus on the self-propulsion of a single droplet in an unbounded fluid, which arises when diffusion is slow enough (i.e. beyond a critical Péclet number, Pec). Despite its experimental relevance, the coupled dynamics of multiple droplets and/or collision with a wall remains mostly unexplored. Using a novel approach based on a moving fitted bispherical grid, the fully-coupled nonlinear dynamics of the chemical solute and flow fields are solved here to characterise in detail the axisymmetric collision of an active droplet with a rigid wall (or with a second droplet). The dynamics is strikingly different depending on the convective-to-diffusive transport ratio, Pe: near the self-propulsion threshold (moderate Pe), the rebound dynamics are set by chemical interactions and are well captured by asymptotic analysis; in contrast, for larger Pe, a complex and nonlinear combination of hydrodynamic and chemical effects set the detailed dynamics, including a closer approach to the wall and a velocity plateau shortly after the rebound of the droplet. The rebound characteristics, i.e. minimum distance and duration, are finally fully characterised in terms of Pe. * Electronic address: sebastien.michelin@ladhyx.polytechnique.fr arXiv:1912.04621v1 [physics.flu-dyn]

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“…The detailed dynamics of the spontaneous transition to steady pumping was analyzed extensively in Ref. [22] for axisymmetric regimes, and we demonstrate below that this transition is not relevant in 3D as symmetric pumping states are unstable. 4.…”

Section: A Axisymmetric Flow Regimesmentioning

confidence: 86%

“…Evolution of the axisymmetric self-propulsion velocity U of an active LC drop with Pe for m1 = 0 (+), m1 = 2 (×), or m1 = −2 (•). The asymptotic prediction for an isotropic drop (m1 = 0) in Ref [22]. is also reported (dashed).…”

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confidence: 96%

Orientational instability and spontaneous rotation of active nematic droplets

Morozov

Michelin

2019

Soft Matter

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In experiments, an individual chemically active liquid crystal (LC) droplet submerged in the bulk of a surfactant solution may self-propel along a straight, helical, or random trajectory. In this paper, we develop a minimal model capturing all three types of self-propulsion trajectories of a drop in the case of a nematic LC with homeotropic anchoring at LC-fluid interface. We emulate the director field within the drop by a single preferred polarization vector that is subject of two reorientation mechanisms, namely, the internal flow-induced displacement of the hedgehog defect and the droplet's rotation. Within this reduced-order model, the coupling between the nematic ordering of the drop and the surfactant transport is represented by variations of the droplet's interfacial properties with nematic polarization. Our analysis reveals that a novel mode of orientational instability emerges from the competition of the two reorientation mechanisms and is characterized by a spontaneous rotation of the self-propelling drop responsible for helical self-propulsion trajectories. In turn, we also show that random trajectories in isotropic and nematic drops alike stem from the advectiondriven transition to chaos. The succession of the different propulsion modes is consistent with experimentally-reported transitions in the shape of droplet trajectories as the drop size is varied. arXiv:1909.06169v1 [cond-mat.soft]

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Nonlinear dynamics of a chemically-active drop: From steady to chaotic self-propulsion

Cited by 72 publications

References 30 publications

Physicochemical hydrodynamics of droplets out of equilibrium

Physicochemical hydrodynamics of droplets out of equilibrium

Collisions and rebounds of chemically active droplets

Orientational instability and spontaneous rotation of active nematic droplets

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