Coalescence of charged droplets in outer fluids

Sadeghi, Hadi Mohammadjafari; Sadri, Behnam; Kazemi, Mohammad Amin; Jafari, Moharram

doi:10.1016/j.jcis.2018.08.001

Cited by 17 publications

(9 citation statements)

References 43 publications

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“…The demonstration involved the on-demand coalescence of the droplets for controlling organic reactions. Manipulation of charged droplets by an electric field has been reported only for aqueous droplets but not for organic droplets; the manipulation of aqueous droplets is important for droplet flow chemistry (e.g., microfluidics) . On the other hand, previous studies have discussed the importance of the organic medium in flow chemistry for many applications, such as performing organic reactions, biochemical assays, self-assembly of colloidal particles, and synthesis of materials; , hence, it will be useful to be able to manipulate charged organic droplets for these applications.…”

Section: Discussionmentioning

confidence: 99%

Charging Organic Liquids by Static Charge

et al. 2020

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Aqueous liquids can be charged effectively by a number of methods for many important applications. Organic liquids, however, cannot be charged effectively by existing methods due to their low conductivities, especially the insulating nonpolar organic liquids; hence, there has not been any significant application developed based on charged organic liquids. This study describes an effective fundamental strategy for charging organic liquids, including nonpolar organic liquids: static charge is simply mixed into the liquid. Analyses suggested that the charged species are molecular ions that reside in the bulk of the liquid after charging. This method is simple and general, and the amount and polarity of charge can be flexibly tunable. The effectiveness of this method gives rise to opportunities for the development of novel applications. Charged organic droplets are manipulated for the first time by an electric field for controlling organic reactions. Particles with charge embedded in their bulk matrices are fabricated for the first time (i.e., via polymerizing the liquid monomers mixed with static charge). The charge in this novel class of bulk-charged particles is stable and permanent, especially when compared to the typical surface-charged particles. Simultaneous bulk-charged and bulk-magnetic particles are fabricated for the first time via simply mixing both the static charge and magnetic nanoparticles into the liquid monomers. These highly versatile particles are responsive to both electric and magnetic fields for practical applications.

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Section: Discussionmentioning

confidence: 99%

Charging Organic Liquids by Static Charge

et al. 2020

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“…Therefore, increasing the electric field strength can shorten the drainage time of the continuous phase due to stronger dipole forces, which is supposed to enhance the efficiency of the droplet coalescence. However, the bridge promptly breaks at sufficiently high field strengths . Subsequently, the droplets recoil from each other.…”

Section: Introductionmentioning

confidence: 99%

“…However, the bridge promptly breaks at sufficiently high field strengths. 6 Subsequently, the droplets recoil from each other.…”

Section: ■ Introductionmentioning

confidence: 99%

Electrocoalescence Criterion of Conducting Droplets Suspended in a Viscous Fluid

et al. 2019

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Coalescence of conducting droplets dispersed in an immiscible medium can be facilitated by an electric field. However, droplets recoil promptly after contact in sufficiently high electric fields if the cone angle between droplets exceeds a critical value. To elucidate the critical condition for droplet coalescence, the behavior of two suspended droplets after contact with a direct current electric field is studied. It is shown that the critical angle is determined not only by the droplet geometry but also conductivity, surfactant concentration, and size. As the droplet conductivity increases, more identical ions accumulate on the adjacent interfaces of two droplets due to the faster ionic migration, which results in Coulombic repulsion between droplets and a reduced critical angle. For surfactant-laden droplets, film drainage induces a surfactant concentration gradient on the leading edges of droplets, and then Marangoni stress is formed to reduce the critical angle. In the case of large droplets, the bridge transiently expands under the action of directional flow caused by further droplet deformation, but eventually breaks due to opposite electrostatic forces. Based on this finding, the electrocoalescence criterion can be determined and employed to facilitate droplet coalescence in various applications.

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“…Contrary to this, the separation in 3D-ESPM was targeted on the water droplets of emulsions. Under the Dean-coupled inertial migration principle from the spiral microchannel [37,38] and the electrostatic forces from the DC electric field [39], different particle sizes resulting in different movement speeds, the droplets are brought close to each other and are coalesced into an aqueous phase with a higher probability. Thus, the clear water phase will appear at the bottom immediately after the emulsion passes through the 3D-ESPM in 3 s. From our previous report, it has been confirmed that only the DC electric field or only the spiral microchannel did not show obvious demulsification efficiency [16].…”

Section: Resultsmentioning

confidence: 99%

Elaboration of the Demulsification Process of W/O Emulsion with Three-Dimensional Electric Spiral Plate-Type Microchannel

Hamiti

et al. 2019

Micromachines

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Rapid and efficient demulsification (destabilizing of an emulsion) processes of a water in oil (W/O) emulsion were carried out in a three-dimensional electric spiral plate-type microchannel (3D-ESPM). In this experiment, the demulsifying efficiency of emulsions by 3D-ESPM was compared with that by gravity settling, the factors influencing demulsifying efficiency were investigated, and the induction period, cut size and residence time in the demulsification process were studied. The results showed that in contrast to the gravity settling method, 3D-ESPM can directly separate the disperse phase (water) instead of the continuous phase (oil). The maximum demulsifying efficiency of W/O emulsion in a single pass through the 3D-ESPM reached 90.3%, with a microchannel height of 200 μm, electric field intensity of 250 V /cm, microchannel angle of 180°, microchannel with 18 plates and a flow rate of 2 mL /min. An induction period of 0.6 s during the demulsification process was simulated with experimental data fitting. When the residence time of emulsion in 3D-ESPM was longer than the induction period, its demulsifying efficiency increased as the increase of the flow velocity due to the droplet coalescence effects of Dean vortices in the spiral microchannel. For this device a cut size of droplets of 4.5 μm was deduced. Our results showed that the demulsification process of W/O emulsion was intensified by 3D-ESPM based on the coupling effect between electric field-induced droplets migration and microfluidic hydrodynamic trapping.

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Coalescence of charged droplets in outer fluids

Cited by 17 publications

References 43 publications

Charging Organic Liquids by Static Charge

Charging Organic Liquids by Static Charge

Electrocoalescence Criterion of Conducting Droplets Suspended in a Viscous Fluid

Elaboration of the Demulsification Process of W/O Emulsion with Three-Dimensional Electric Spiral Plate-Type Microchannel

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