Spontaneously rotating clusters of active droplets

Hokmabad, Babak Vajdi; Nishide, Akemi; Ramesh, Prashanth; Krüger, Carsten; Maaß, Corinna C.

doi:10.1039/d1sm01795k

Cited by 43 publications

(39 citation statements)

References 58 publications

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“…Complex collective behavior can result from intricate biological mechanisms but also, can be solely caused by nonequilibrium dynamics (refs. 10 – 14 have such examples), such that there is a need to untangle physics and biology. To this end, current research in artificial active matter aims to design and develop synthetic microswimmers that can mimic strategies like chemotaxis by purely physicochemical means ( 15 ).…”

mentioning

confidence: 99%

Chemotactic self-caging in active emulsions

Hokmabad

Agudo-Canalejo

Saha

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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A common feature of biological self-organization is how active agents communicate with each other or their environment via chemical signaling. Such communications, mediated by self-generated chemical gradients, have consequences for both individual motility strategies and collective migration patterns. Here, in a purely physicochemical system, we use self-propelling droplets as a model for chemically active particles that modify their environment by leaving chemical footprints, which act as chemorepulsive signals to other droplets. We analyze this communication mechanism quantitatively both on the scale of individual agent–trail collisions as well as on the collective scale where droplets actively remodel their environment while adapting their dynamics to that evolving chemical landscape. We show in experiment and simulation how these interactions cause a transient dynamical arrest in active emulsions where swimmers are caged between each other’s trails of secreted chemicals. Our findings provide insight into the collective dynamics of chemically active particles and yield principles for predicting how negative autochemotaxis shapes their navigation strategy.

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mentioning

confidence: 99%

Chemotactic self-caging in active emulsions

Hokmabad

Agudo-Canalejo

Saha

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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“…The asymmetric trails are likely the cause of the significant lateral motion associated with these droplets, since Marangoni forces arise from asymmetry in interfacial tension gradients, which can be directly attributed to chemical gradients in active droplets. Hokmabad et al [15,22,28] saw similar features in the chemical trails of chaotic active droplets in a dish. In particular, they visualized the formation of a plume of filled micelles using fluorescence and showed that this plume was correlated to droplet reorientation events.…”

Section: Resultsmentioning

confidence: 86%

“…Notably, the settling active droplets were found to undergo transient motion against the direction of gravity. Hokmabad et al [15] have studied the self-assembly of active droplets at the bottom of a dish to form a hexagonal cluster, followed by their spontaneous rise and rotation. Recent theoretical and numerical studies have suggested that an external force field could have a significant impact on active droplet motion [16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Gravitational settling of active droplets

Castonguay

Kailasham

Wentworth

et al. 2022

Preprint

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The gravitational settling of oil droplets solubilizing in an aqueous micellar solution contained in a capillary channel is investigated. The motion of these active droplets reflects a competition between gravitational and Marangoni forces, the latter due to interfacial tension gradients generated by differences in filled- micelle concentrations along the oil-water interface. This competition is studied by varying the surfactant concentration, the density difference between the droplet and the continuous phase, and the viscosity of the continuous phase. The Marangoni force enhances the settling speed of an active droplet when compared to the Hadamard-Rybczynski prediction for a (surfactant free) droplet settling in Stokes flow. The Marangoni force can also induce lateral droplet motion, suggesting that the Marangoni and gravitational forces are not always aligned. The decorrelation rate (𝛼) of the droplet motion, measured as the initial slope of the velocity autocorrelation and indicative of the extent to which the Marangoni and gravitational forces are aligned during settling, is examined as a function of the droplet size: correlated motion (small values of 𝛼) is observed at both small and large droplet radii, whereas significant decorrelation can occur between these limits. This behavior of active droplets settling in a capillary channel is in marked contrast to that observed in a dish, where the decorrelation rate increases with the droplet radius before saturating at large values of droplet radius. A simple relation for the crossover radius at which the maximal value of 𝛼 occurs for an active settling droplet is proposed.

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“…[42] showed that developing starfish embryos generate different flow patterns during its development process, which determine their self-organisation (formation, dynamics, and dissolution) into living crystals. Analogously, in artificial autophoretic systems, rotational instabilities on the individual scale [10,39] can carry through to the collective dynamics, where we have recently found Pe dependent stability and collective rotation in self-assembled planar clusters [43]. Here, the superposition of self-generated chemical fields might well provide a mechanism for the emergence of stable collective rotational states.…”

Section: Discussion and Outlookmentioning

confidence: 89%

Interfacial activity dynamics of confined active droplets

Ramesh¹,

Hokmabad²,

Rahalia³

et al. 2022

Preprint

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Oil droplets in aqueous surfactant solution show spontaneous self-propulsion and dynamics ranging from straight-line to unsteady motion with increasing Péclet number. Recent studies have shown that products of interfacial activity (oil-filled micelles) can lead to multistable higher-mode flow fields and chemorepulsive phenomena. To investigate such chemodynamic effects, we have studied disk-like flattened droplets that are pinned at the top and bottom of the reservoir and produce only pumping flow. With increasing droplet radius we observe the following: (i) vortical structures generated by the droplet migrating around the interface, (ii) bistability between a dipolar and quadrupolar flow mode, and, eventually, (iii) a transition to multipolar modes. For a deeper analysis, we measured flow fields by particle image velocimetry and compared them to a hydrodynamic model based on a Brinkman squirmer. A simultaneous quantification of the flow fields and oil-filled micelle distribution suggests that a local buildup of chemical products leads to a saturation of the surface, which affects the propulsion mechanism. Hence, we describe the interfacial activity dynamics in time and space.

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Spontaneously rotating clusters of active droplets

Abstract: We report on the emergence of spontaneously rotating clusters in active emulsions. Ensembles of self-propelling droplets sediment and then self-organise into planar, hexagonally ordered clusters which hover over the container...

Cited by 43 publications

References 58 publications

Chemotactic self-caging in active emulsions

Chemotactic self-caging in active emulsions

Gravitational settling of active droplets

Interfacial activity dynamics of confined active droplets

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