Chemical reaction-driven tip-streaming phenomena in a pendant drop

Fernández, Juan Manuel; Homsy, G. M.

doi:10.1063/1.1739231

Cited by 25 publications

(45 citation statements)

References 23 publications

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“…2(a), self-driven Marangoni singularities have not been thoroughly studied. Marangoni-driven flows exhibiting interfacial singularities, which motivated the present study, were found experimentally only recently [19,[36][37][38][39] and are shown in Figs. 2(b) and 2(c).…”

supporting

confidence: 64%

“…(7) Let us identify the conditions under which a solution local near a cusp singularity exists in the Stokes approximation. The corresponding stream function (6) satisfies the kinematic boundary condition (3) provided [17,35] -viscous stresses in the surrounding phase deform the drop, which forms pointed ends; (b) chemical reaction-driven tip streaming [19,36,37] -the acid-base chemical reaction at the water-oil interface produces a surfactant, which drives the Marangoni flow along the interface leading to a conical shape of the drop with a singular cone tip', (c) surfactant-driven fingering [38,39]-soapy water displaces air in the narrow space between two glass plates (Hele-Shaw cell) and eventually leads to fingering with cusps between the fingers. 043019-2 CUSPS AND CUSPIDAL EDGES AT FLUID INTERFACES: ... which allows us to rewrite the formula (6) as…”

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confidence: 99%

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Cusps and cuspidal edges at fluid interfaces: Existence and application

Krechetnikov

2015

Phys. Rev. E

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One of the intriguing questions in fluid dynamics is on the interrelation between dynamic singularities in the solutions of fluid dynamic equations - unboundedness of the velocity field in an appropriate norm - and the geometric ones - divergence of curvature at fluid interfaces. The present work focuses on two generic interfacial singularities - genuine cusps and cuspidal edges - found here in both two and three dimensions thus establishing a relation between real fluid interfaces and geometric singularity theory. The key finding is the necessary condition for the existence of geometric singularities, which is a variation of surface tension. It is also established here that the dynamic and geometric singularities entail each other only in the case of three-dimensional cusps. Explicit asymptotic solutions for the flow field and interface shape near steady-state singularities at fluid interfaces are developed as well. The practical motivation for the present study comes from the fundamental role interfacial singularities play in sustaining self-driven conversion of chemical into mechanical energy.

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confidence: 64%

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confidence: 99%

Cusps and cuspidal edges at fluid interfaces: Existence and application

Krechetnikov

2015

Phys. Rev. E

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“…Our thread formation and tipstreaming observations also closely resemble recent work in which tipstreaming was observed as a result of a chemical reaction that produces surfactant at an oil-water interface. 48 During pendant drop measurements of the dynamic surface tension, the authors observed that on occasions in which the pendant drop breaks off and settles in the outer liquid bath, this pinchoff is followed by tipstreaming of tiny droplets, in this case ϳ4 micrometers, for a sustained period of time. The authors offer physical arguments that this process results from strong surface tension gradients and they show that an apparent capillary number for the process is approximately Ca Ϸ 0.5 as is expected for classic tipstreaming.…”

Section: -9mentioning

confidence: 99%

Microscale tipstreaming in a microfluidic flow focusing device

2006

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A microfluidic flow-focusing device is used to explore the use of surfactant-mediated tipstreaming to synthesize micrometer-scale and smaller droplets. By controlling the surfactant bulk concentration of a soluble nonionic surfactant in the neighborhood of the critical micelle concentration, along with the capillary number and the ratio of the internal and external flow rates, we observe several distinct modes of droplet breakup. For the most part, droplet breakup in microfluidic devices results in highly monodisperse droplets in the range of tens of micrometers in size. However, we observe a new mode of breakup called "thread formation" that resembles tipstreaming and yields tiny droplets in the range of a few micrometers in size or smaller. In this work, we characterize the growth of the thread and its maximum length as a function of flow variables and surfactant content, and we also characterize the period of droplet breakup as a function of these variables. Our results suggest possible methods for controlling the process. Using a simple flow visualization experiment as the basis, we report on preliminary efforts to model the thread formation process.

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“…In this context, the peculiar observation of the spontaneous motion of a water-alkali pendant drop at the tip of a capillary in the oil-acid environment reported by Fernandez and Homsy 15 (FH) was a promising finding, cf. Figure 1, named chemical reaction-driven tip-streaming (CRDTS).…”

Section: A Chemical-reaction Driven Tip-streamingmentioning

confidence: 98%

The nature of chemical reaction-driven tip-streaming

Mayer

Krechetnikov

2013

Journal of Applied Physics

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The discovery of chemical reaction-driven tip-streaming (also known as "an amazing drop") was made about a decade ago during measurements of the dynamic interfacial tension of a water-alkali pendant droplet immersed in oil-linoleic acid. A plausible explanation for this self-sustained ejection of micron sized droplets from the tip of the macroscopic pendant drop was offered at that time and attributed to Marangoni stresses driving the reaction-produced surfactant along the interface. Later, asymptotic theory based on the analysis of a complete fluid dynamical formulation supported this hypothesis. As this discovery promised a way of microdroplet generation without the need for complex microchannel geometries or externally imposed flow or electric fields, we were recently motivated to study the influence of the reagent concentrations and reaction rate on the droplet generation. However, in an attempt to recreate the original experiments, we revealed that the cause for tip-streaming is not what it originally seemed to be. This led to a series of experiments clarifying the role of the Marangoni stresses and the crucial differences from similar phenomena. As the mechanism by which the phenomenon was originally thought to operate was supported by recent theoretical studies, the present work leads to new intriguing questions of existence and conditions under which a chemical reaction alone can drive Marangoni stresses capable of self-sustaining the process of tip-streaming. V

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Chemical reaction-driven tip-streaming phenomena in a pendant drop

Cited by 25 publications

References 23 publications

Cusps and cuspidal edges at fluid interfaces: Existence and application

Cusps and cuspidal edges at fluid interfaces: Existence and application

Microscale tipstreaming in a microfluidic flow focusing device

The nature of chemical reaction-driven tip-streaming

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