Jet and progeny formation in the Rayleigh breakup of a charged viscous drop

Gawande, Neha; Mayya, Y. S.; Thaokar, Rochish

doi:10.1017/jfm.2019.970

Cited by 22 publications

(31 citation statements)

References 54 publications

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“…35) [352][353][354]. The problem has been numerically solved considering both the leaky-dielectric model [355,356] and electrokinetic effects [92,96,357]. The periodic or steady ejection produced by tip streaming in the microfluidic configurations described in Sec.…”

Section: Electrohydrodynamic Tip Streamingmentioning

confidence: 99%

Dripping, jetting and tip streaming

2020

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Dripping, jetting and tip streaming have been studied up to a certain point separately by both fluid mechanics and microfluidics communities, the former focusing on fundamental aspects while the latter on applications. Here, we intend to review this field from a global perspective by considering and linking the two sides of the problem. In the first part, we present the theoretical model used to study interfacial flows arising in droplet-based microfluidics, paying attention to three elements commonly present in applications: viscoelasticity, electric fields and surfactants. We review both classical and current results about the stability of jets affected by these elements. Mechanisms leading to the breakup of jets to produce drops are reviewed as well, including some recent advances in this field. We also consider the relatively scarce theoretical studies on the emergence and stability of tip streaming in open systems. In the second part of this review, we focus on axisymmetric microfluidic configurations which can operate on the dripping and jetting modes either in a direct (standard) way or via tip streaming. We present the dimensionless parameters characterizing these configurations, the scaling laws which allow predicting the size of the resulting droplets and bubbles, as well as those delimiting the parameter windows where tip streaming can be found. Special attention is paid to electrospray and flow focusing, two of the techniques more frequently used in continuous drop production microfluidics. We aim to connect experimental observations described in this section of topics with fundamental and general aspects described in the first part of the review. This work closes with some prospects at both fundamental and practical levels.

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Section: Electrohydrodynamic Tip Streamingmentioning

confidence: 99%

Dripping, jetting and tip streaming

2020

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“…Two important modes of breakups are reported, such as end pinching and tip streaming [ 114 , 115 ]. In the former mode, the droplet is converted into bulbous-shaped lobes that eventually disintegrate, whereas in the latter case, the droplet develops sharp cone-like tips ejecting jets.…”

Section: Single-phase Emulsion Dropletsmentioning

confidence: 99%

“…For a low-conducting droplet, the jet vanishes, and the breakup is via end-pinching due to rapid domination of capillary stresses. It is also notable that with a decrease in droplet conductivity, the jet length first increases, reaches a maximum

, and then it decreases [ 114 ]. It is also reported that a change of mode can also take place due to surface charge convection effects represented by

, as shown in Figure 4 D [ 115 ].…”

Section: Single-phase Emulsion Dropletsmentioning

confidence: 99%

“…( B ) Non-dimensional stretching vs. electric capillary number leading to instability (reproduced from [ 15 ] with permission from The Royal Society of Chemistry). ( C ) Effects of viscosity ratio and liquid conductivity (in terms of Saville number) on the droplet shapes [ 114 ]. ( D ) Droplet breakup mode transition depending on electric Reynolds Number [ 115 ].…”

Section: Figurementioning

confidence: 99%

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Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications

et al. 2020

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The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in many ways over the next 55 years with numerous intriguing phenomena reported, such as tip and equatorial streaming, Quincke rotation, double droplet breakup modes, particle assemblies at the emulsion interface, and many more. These phenomena have a potential of vast applications in different areas of science and technology. This paper presents a review of prominent droplet EHD studies pertaining to the essential physical insight of various EHD phenomena. Here, we discuss the dynamics of a single-phase emulsion droplet under weak and strong electric fields. Moreover, the effect of the presence of particles and surfactants at the emulsion interface is covered in detail. Furthermore, the EHD of multi-phase double emulsion droplet is included. We focus on features such as deformation, instabilities, and breakups under varying electrical and physical properties. At the end of the review, we also discuss the potential applications of droplet EHD and various challenges with their future perspectives.

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“…The unsteady disintegration of charged and neutral drops under externally applied electric fields constitutes a fundamental electrohydrodynamic problem with enormous relevance in natural and technological processes. This tip streaming phenomenon has been analyzed theoretically over the last decades [13][14][15][16][17][18][19][20][21] assuming perfect volumetric charge relaxation and ohmic conduction (the so-called leaky-dielectric model) 13,16,17,21 . Some studies have also considered certain electrokinetic effects along the process, including volumetric charge relaxation phenomena 14,[18][19][20] .…”

Section: Introductionmentioning

confidence: 99%

Diameter and charge of the first droplet emitted in electrospray

et al. 2021

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The first droplet produced by a low-conductivity pendant/sessile droplet subject to a strong electric field is particularly important at the fundamental level because, in contrast to steady electrospray phenomena, its ejection entails complex charge relaxation and electrokinetic processes. Besides, it is technologically relevant because of its very small diameter and large electric charge per unit volume. In this work, we present an experimental technique to measure with unprecedented accuracy the diameter of the droplet and to determine for the first time its electric charge. We discuss both the advantages of our technique over possible alternatives and the limitations of the method. The proposed method is applied to two alcohols with electrical conductivities of the order of a few μS/m. The high sensitivity of our experimental technique allows us to determine the influence of both the magnitude and the polarity of the applied voltage on the size and charge of the ejected droplet. The electric charge of the first-emitted droplet lies in the interval 0.51≲q/qR≲0.66 (qR is the Rayleigh limit of charge) for the two liquids analyzed. These experimental values are slightly larger than those obtained from theoretical predictions. The value of q/qR for the first droplet is very relevant because it can be regarded as an upper bound of those of the droplets subsequently emitted in the cone-jet mode of electrospray.

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Jet and progeny formation in the Rayleigh breakup of a charged viscous drop

Cited by 22 publications

References 54 publications

Dripping, jetting and tip streaming

Dripping, jetting and tip streaming

Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications

Diameter and charge of the first droplet emitted in electrospray

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