Towards active microfluidics: Interface turbulence in thin liquid films with floating molecular machines

Alonso, Sergio; Mikhailov, Alexander S.

doi:10.1103/physreve.79.061906

Cited by 16 publications

(32 citation statements)

References 27 publications

(31 reference statements)

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“…The induced fluid flow moves additional swimmers towards the bulge and increases the local excess pressure further. The interface becomes unstable if the combined stabilizing effect of translational diffusion and Marangoni flow towards regions of smaller swimmer concentrations is too weak [21].In this letter we show that self-propelled motion of the swimmer parallel to the liquid-gas interface (in-plane motion) together with rotational diffusion has a profound and non-trivial effect on the stability of the film. Depending on the strength of rotational diffusion and swimming velocity, the in-plane motion can stabilize a flat film or induce film instabilities of different character.…”

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confidence: 75%

“…[21]. Next we assess whether this also applies for the stabilization of the film due to the combined action of the rotational diffusivity D and the in-plane velocity V , reported here.…”

mentioning

confidence: 92%

“…This case corresponds to particles that only swim perpendicularly to the free surface as studied in Ref. [21]. The corresponding dispersion relation Re(γ) vs. k is plotted as heavy solid line in Fig.…”

mentioning

confidence: 97%

“…Namely, Ref. [21] investigates a monolayer of insoluble swimmers that are adsorbed at the free surface of a liquid film and exclusively swim into the direction perpendicular to the surface. That is, they are "head up", at all times and their motion along the liquid-gas interface is as for passive particles.…”

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confidence: 99%

“…[21]. Here, ρ (x, y, t) = 2π 0 ρ(x, y, φ, t) dφ denotes the local particle density averaged over all swimming directions and α = p z v 0 /M with p z = P (p z )p z dp z is the negative of the force the interface exerts on the swimming particles in order to stop them in vertical direction [27].…”

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confidence: 99%

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Stability of liquid films covered by a carpet of self-propelled surfactant particles

2014

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We consider a carpet of self-propelled particles at the liquid-gas interface of a liquid film on a solid substrate. The particles excert an excess pressure on the interface and also move along the interface while the swimming direction performs rotational diffusion. We study the intricate influence of these self-propelled insoluble surfactants on the stability of the film surface and show that depending on the strength of in-surface rotational diffusion and the absolute value of the in-surface swimming velocity several characteristic instability modes can occur. In particular, rotational diffusion can either stabilize the film or induce instabilities of different character. The understanding of the physical principles of the motion of self-propelled particles in viscous fluids [1][2][3][4][5][6], either in the bulk or at interfaces is of primary importance for an increasing number of applications in microfluidics and medicine [7][8][9]. A particularly interesting emerging application of such swimmers are biocoatings formed using a suspension of living cells that is deposited onto a solid substrate before the solvent is removed, e.g., by evaporation. This technique is used to fabricate bacterial carpets consisting of living bacteria with rotating flagella that are attached head down to a polymer layer [10]. The created homogeneous monolayer of living cells is seen as a prototype of a novel biomaterial with remarkable applications, e.g., as artificial skin, self-cleaning coating, or biosensor [11][12][13][14][15]. Beside applications in biotechnology, free liquid-gas interfaces loaded with motile bacteria occur naturally, for example, at the sea surface [16]. Microswimmers at the interface of a thin liquid film also show interesting collective phenomena since even in a dilute suspension they interact with each other through the surface flow field initiated by gradients in the surface tension and curvatures in the height profile. In the following, we present an analysis of the stability of such thin films and demonstrate the subtle influence of in-plane swimming velocity and rotational diffusivity.The proximity of swimmers to the liquid-gas interface inevitably modifies the local surface tension, which depends on the swimmer concentration similar to passive surfactant molecules and (nano-)particles [17][18][19][20]. A gradient in the surface tension due to a non-uniform concentration generates fluid flow at the surface (solutocapillary Marangoni effect), a phenomenon well studied for passive surfactants. The impact of self-propelled surfactants, i.e., surfactants that are capable to move autonomously, on the dynamics of liquid-gas interfaces (free surfaces), has been studied only in one special case. Namely, Ref.[21] investigates a monolayer of insoluble swimmers that are adsorbed at the free surface of a liquid film and exclusively swim into the direction perpendicular to the surface. That is, they are "head up", at all times and their motion along the liquid-gas interface is as for passive particles. As a result,...

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mentioning

confidence: 75%

“…[21]. Next we assess whether this also applies for the stabilization of the film due to the combined action of the rotational diffusivity D and the in-plane velocity V , reported here.…”

mentioning

confidence: 92%

mentioning

confidence: 97%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Stability of liquid films covered by a carpet of self-propelled surfactant particles

2014

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Dynamische Kopplung bei niedriger Reynoldszahl

Dey

2019

Angewandte Chemie

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Aktive Kolloide, bei denen kollektives und emergentes Verhalten auftritt, gewähren nützliche Einblicke in die statistische Physik von Nichtgleichgewichtssystemen. Um die Prinzipien des Energietransfers unter den Bedingungen einer niedrigen Reynoldszahl kennenzulernen, hat man Kolloidsuspensionen untersucht, die aktive Mikroschwimmer enthalten. Studien an aktiven Enzymen und metallorganischen Katalysatoren im Ångström‐Bereich belegten, dass bereits Moleküle Energie auf ihre Umgebung übertragen und dadurch die Gesamtdynamik des Systems substantiell beeinflussen können. Anhand der Diffusion von unreaktiven Tracern in einer aktiven Lösung wurde gezeigt, dass der Energietransfer in Systemen mit unterschiedlichen Schwimmern ähnlich abläuft – ungeachtet der Größe, der Art der Energieübertragung und des Antriebssystems des Schwimmers. Dieser Aufsatz diskutiert bisherige Forschungsergebnisse und die beobachteten Gemeinsamkeiten bei der dynamischen Kopplung von Schwimmern mit der Umgebung.

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Dynamic Coupling at Low Reynolds Number

Dey

2019

Angew Chem Int Ed

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Collective and emergent behaviors of active colloidal assemblies provide useful insights into the statistical physics of out-of-equilibrium systems. Colloidal suspensions containing microscopic active swimmers have recently been studied with much vigor to understand principles of energy transfer at low Reynolds number conditions. Using molecules of active enzymes and ångström sized organometallic catalysts it has further been demonstrated that energy can be transferred even by molecules to their surroundings, influencing substantially the overall dynamics of the systems. Monitoring the diffusion of non-reacting tracers dispersed in active solutions, it has been shown that the nature of energy transfer in systems containing different swimmers is surprisingly similar - irrespective of their differences in sizes, modes of energy transduction and propulsion strategies. These observations provide motivation not only to characterize reaction generated force fields under complex fluidic environment but also to look for possible similarity in their behavior across multiple length scales. This review discusses research results obtained so far in this direction, highlighting the common features observed regarding dynamic coupling of swimmers with their surroundings. Activity-induced force generation and its collective effects are expected to find wide importance in transport and organization of materials at smaller length scales. Underscoring the nature of reaction generated perturbations, especially under crowded cytosolic conditions, is further likely to advance our knowledge of intracellular mechanics of small molecules during various metabolic processes and chemical transformations.

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Towards active microfluidics: Interface turbulence in thin liquid films with floating molecular machines

Cited by 16 publications

References 27 publications

Stability of liquid films covered by a carpet of self-propelled surfactant particles

Stability of liquid films covered by a carpet of self-propelled surfactant particles

Dynamische Kopplung bei niedriger Reynoldszahl

Dynamic Coupling at Low Reynolds Number

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