Electrically modulated relaxation dynamics of pre-stretched droplets post switched-off uniaxial extensional flow

Behera, Nalinikanta; Chakraborty, Suman

doi:10.1039/d1sm01813b

Cited by 7 publications

(8 citation statements)

References 75 publications

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“…The ratios between the different physical properties of ith and jth fluid are defined as λ ij (= μ i /μ j ), R ij (= σ i /σ j ) and S ij (= ε i /ε j ), where i, j = 1, 2 and 3. These notations are in accordance with the previous works reported on related topics (Lac & Homsy 2007;Das & Saintillan 2017;Poddar et al 2019b;Sorgentone et al 2021;Behera & Chakraborty 2022) The surface tensions at the two interfaces are denoted as γ 12 and γ 23 . Under the action of electric-field-induced forces, the inner and outer drops translate with velocities of U 1 and U 2 , respectively, which are a priori unknown and are to be obtained from the model calculations.…”

Section: Theorysupporting

confidence: 61%

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Eccentricity-induced dielectrophoretic migration of a compound drop in a uniform external electric field

2023

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Eccentric compound drops, which are ubiquitous in many naturally inspired and engineering systems, can migrate under the sole presence of a uniform electric field, unlike the case of isolated single drops. Here, we report the migration of eccentric compound drops under a uniform electric field, imposed parallel to the line of centres of the constituting drops, by developing an approximate analytical model that applies to low Reynolds number limits under negligible droplet deformation, following axisymmetric considerations. In contrast to the sole influence of the electrohydrodynamic forces that has thus far been established to be emphatic for the eccentric configuration, here we report the additional effects induced by the dielectrophoretic forces to result in decisive manipulation in the drop migration. We show that the relative velocity between the inner and outer drops, which is a function of the eccentricity itself, dictates the dynamical evolution of the eccentricity variation under the competing electrohydrodynamic and dielectrophoretic interactions. This brings out four distinct regimes of the migration characteristics of the two drops based on their relative electro-physical properties. Our results reveal that an increase in eccentricity and the size ratio of the inner and outer droplets may induce monotonic or non-monotonic variation in the drop velocities, depending on the operating regime. We show how the interplay of various properties holds the control of selectively increasing or suppressing the eccentricity with time. These findings open up various avenues of electrically manipulative motion of encapsulated fluidic phases in various applications encompassing engineering and biology.

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Section: Theorysupporting

confidence: 61%

“…2019 b ; Sorgentone et al. 2021; Behera & Chakraborty 2022) The surface tensions at the two interfaces are denoted as and . Under the action of electric-field-induced forces, the inner and outer drops translate with velocities of and , respectively, which are a priori unknown and are to be obtained from the model calculations.…”

Section: Theorymentioning

confidence: 99%

Eccentricity-induced dielectrophoretic migration of a compound drop in a uniform external electric field

2023

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“…Similarly, the coeffect of We e and Ca in relaxation dynamics of castor droplets in silicon oil has been explored under uniaxial extensional flow electrified environments. 38 The regime diagram on We e −Ca space shows that the increase in ether We e or Ca contributes to the transition of the droplet state from stable to unstable. Therefore, when the droplet is exposed to an electric field and external flows, the We e is a more appropriate and critical criterion for the regime prediction in this article.…”

Section: ■ Resultsmentioning

confidence: 99%

“…The interplay of We e , representing the electric force, and Ca, standing for the viscous force, dominates droplet behaviors and leads to novel drop evolution. 38 Therefore, we propose the We e Ca as one of the important criterions, which is the ratio of the product of viscous and electric forces to the squared interfacial tension. It represents the balance between the viscous and electric forces, which tend to deform the droplet, and the interfacial tension, which maintains the stability of the droplet shape.…”

Section: ■ Introductionmentioning

confidence: 99%

Characteristics of Oil-in-Oil Emulsions under AC Electric Fields

Fang,

Tao,

et al. 2024

Langmuir

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Emulsions have been applied in a number of industries such as pharmaceutics, cosmetics, and food, which are also of great scientific interest. Although aqueous emulsions are commonly used in our daily life, oil-in-oil (o/o) emulsions also play an irreplaceable role in view of their unique physics and complementary applications. In this paper, we investigate typical behaviors of organic droplets surrounded by organic medium (o/o emulsions) with different functional groups controlled by the AC electric field. Droplet behaviors can be catalogued into five types: namely, "no effect", "movement", "deformation", "interface rupture", and "disorder". We identify the key dimensionless number We e •Ca, combined with the channel geometry, for characterizing the typical behaviors in silicon oil/1,6-hexanediol diacrylate and mineral oil/1,6-hexanediol diacrylate emulsions. Unlike aqueous emulsion, the Maxwell−Wagner relaxation inhibits the electric effect and leads to an effective frequency, ranging from 0.5 to 3 kHz. The increasing viscosity of the droplet facilitates the escalation by promoting the shearing effect under the same flow conditions. Ethylene glycol droplets primarily show the efficient coalescence even at a low We e • Ca, which is attributed to the attraction of free charges induced by the increasing conductivity. In 1,6-hexanediol diacrylate/silicon oil emulsion, the droplet tends to form a liquid film that expands into the entire channel due to the affinity of the droplet to the channel wall. A variety of elongated columns are observed to oscillate between the electrodes at high voltages. These findings can contribute to understanding the electrohydrodynamic physics in o/o emulsion and controlling droplet behaviors in a fast response, programmable, and high-throughput way. We expect that this droplet manipulation technology can be widely adopted in a broad range of chemical synthesis and biological and material science.

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“…We adopt both gradient-based and curvature-based adaptive mesh refinement (AMR), similar to that used in the recent article of Behera & Chakraborty (2022), to discretize the domain in an effort to minimize the computational cost significantly. The gradient-based AMR is used to compute the volume fraction.…”

Section: Methodsmentioning

confidence: 99%

Electric-field-mediated morpho-dynamic evolution in drop–drop coalescence phenomena in the inertio-capillary regime

Behera

Chakraborty

2023

J. Fluid Mech.

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When two drops collide, they may either exhibit complete coalescence or selectively generate secondary drops, depending on their relative sizes and physical properties, as dictated by a decisive interplay of the viscous, capillary, inertia and gravity effects. Electric field, however, is known to induce distinctive alterations in the topological evolution of the interfaces post-collision, by influencing a two-way nonlinear coupling between electro-mechanics and fluid flow as mediated by a topologically intriguing interfacial deformation. While prior studies primarily focused on the viscous-dominated regime of the resulting electro-coalescence dynamics, several non-intuitive features of the underlying morpho-dynamic evolution over the intertio-capillary regime have thus far remained unaddressed. In this study, we computationally investigate electrically modulated coalescence dynamics along with secondary drop formation mechanisms in the inertio-capillary regime, probing the interactions of two unequal-sized drops subjected to a uniform electric field. Our results bring out an explicit mapping between the observed topological evolution as a function of the respective initial sizes of the parent drops as well as their pertinent electro-physical property ratios. These findings establish electric-field-mediated exclusive controllability of the observed topological features, as well as the critical conditions leading to the transition from partial to complete coalescence phenomena. In a coalescence cascade, an electric field is further shown to orchestrate the numbers of successive stages of coalescence before complete collapse. However, an increase of the numbers of cascade stages with the electric field strength and parent droplet size ratio is non-perpetual, and the same is demonstrated to continue until only a threshold number of cascade stages is reached. These illustrations offer significant insights into leveraging the interplay of electrical, inertial and capillary-driven interactions for controllable drop manipulation via multi-drop interactions for a variety of applications ranging from chemical processing to emulsion technology.

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Electrically modulated relaxation dynamics of pre-stretched droplets post switched-off uniaxial extensional flow

Abstract: Droplets are known to elongate in extensional flow and exhibit capillary instabilities following flow cessation. Under several practical scenarios, where the deformed drops are exposed to electrified environments, the interplay...

Cited by 7 publications

References 75 publications

Eccentricity-induced dielectrophoretic migration of a compound drop in a uniform external electric field

Eccentricity-induced dielectrophoretic migration of a compound drop in a uniform external electric field

Characteristics of Oil-in-Oil Emulsions under AC Electric Fields

Electric-field-mediated morpho-dynamic evolution in drop–drop coalescence phenomena in the inertio-capillary regime

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