Self-Organized Ordered Arrays of Core−Shell Columns in Viscous Bilayers Formed by Spatially Varying Electric Fields

Reddy, P. Dinesh Sankar; Bandyopadhyay, Dipankar; Sharma, Ashutosh

doi:10.1021/jp106253k

Cited by 30 publications

(42 citation statements)

References 131 publications

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“…Further, the interfacial tension of the liquid–liquid configuration is at least an order of magnitude lower than the similar gas–liquid systems. In addition to this, the external field induced transport behaviors of the liquid–liquid flows find important applications in microscale pumping, mixing, separation, reaction, heat, and mass transfer . Recent works indicate that the influence of an external electric field can cause interesting transitions in the liquid–liquid multiphase flow patterns due to the electrohydrodynamic (EHD) stress at the interface originating from the accumulation of induced dipoles or free charges .…”

Section: Introductionmentioning

confidence: 99%

Localized electric field induced transition and miniaturization of two‐phase flow patterns inside microchannels

et al. 2014

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Strategic application of external electrostatic field on a pressure-driven two-phase flow inside a microchannel can transform the stratified or slug flow patterns into droplets. The localized electrohydrodynamic stress at the interface of the immiscible liquids can engender a liquid-dielectrophoretic deformation, which disrupts the balance of the viscous, capillary, and inertial forces of a pressure-driven flow to engender such flow morphologies. Interestingly, the size, shape, and frequency of the droplets can be tuned by varying the field intensity, location of the electric field, surface properties of the channel or fluids, viscosity ratio of the fluids, and the flow ratio of the phases. Higher field intensity with lower interfacial tension is found to facilitate the oil droplet formation with a higher throughput inside the hydrophilic microchannels. The method is successful in breaking down the regular pressure-driven flow patterns even when the fluid inlets are exchanged in the microchannel. The simulations identify the conditions to develop interesting flow morphologies, such as (i) an array of miniaturized spherical or hemispherical or elongated oil drops in continuous water phase, (ii) "oil-in-water" microemulsion with varying size and shape of oil droplets. The results reported can be of significance in improving the efficiency of multiphase microreactors where the flow patterns composed of droplets are preferred because of the availability of higher interfacial area for reactions or heat and mass exchange.

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Section: Introductionmentioning

confidence: 99%

Localized electric field induced transition and miniaturization of two‐phase flow patterns inside microchannels

et al. 2014

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“…Thus at a given IL lm thickness there is always a constant difference between osmotic pressure and electrostatic pressure in eqn (16). The term P c can be found from a stress balance at the lm interface.…”

Section: Electrostatic Pressurementioning

confidence: 99%

“…Applying a transverse electric eld induces the electric pressure (Maxwell stress) at the lm interface that perturbs the pressure balance and enhances the most unstable wavelength of growing instabilities on the lm interface. Various structures form on the polymer surface depending on the initial lling ratio (ratio of initial lm thickness to electrode distance) of the polymer lm, 15 the electric permittivity ratio of layers (lm and bounding media), 16,17 the shape of the electrodes 16,17 and the surface energy of the electrodes and the polymer lm. 18,19 Fig.…”

Section: Introductionmentioning

confidence: 99%

Electrohydrodynamic patterning of ultra-thin ionic liquid films

et al. 2015

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In the electrohydrodynamic (EHD) patterning process, electrostatic destabilization of the air-polymer interface results in micro- and nano-size patterns in the form of raised formations called pillars. The polymer film in this process is typically assumed to behave like a perfect dielectric (PD) or leaky dielectric (LD). In this study, an electrostatic model is developed for the patterning of an ionic liquid (IL) polymer film. The IL model has a finite diffuse electric layer which overcomes the shortcoming of assuming infinitesimally large and small electric diffuse layers inherent in the PD and LD models respectively. The process of pattern formation is then numerically simulated by solving the weakly nonlinear thin film equation using finite difference with pseudo-staggered discretization and an adaptive time step. Initially, the pillar formation process in IL films is observed to be the same as that in PD films. Pillars initially form at random locations and their cross-section increases with time as the contact line expands on the top electrode. After the initial growth, for the same applied voltage and initial film thickness, the number of pillars on IL films is found to be significantly higher than that in PD films. The total number of pillars formed in 1 μm(2) area of the domain in an IL film is almost 5 times more than that in a similar PD film for the conditions simulated. In addition, the pillar structure size in IL films is observed to be more sensitive to initial film thickness compared to PD films.

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“…For example, an external electric field have been employed to engender droplet coalescence , splitting and sorting where the accumulation of induced or free charges at the interface plays a crucial role in developing the miniaturized flow morphologies. There are evidences that the electrohydrodynamic (EHD) stress can be strong enough to deform a soft interface to produce miniaturized flow structures with significantly higher surface to volume ratio . The major advantage in this methodology is its non‐invasive nature of operation, which points to the fact that they can be integrated easily to any of the microfluidic applications without influencing the other process parameters.…”

Section: Introductionmentioning

confidence: 99%

Discrete electric field mediated droplet splitting in microchannels: Fission, Cascade, and Rayleigh modes

et al. 2016

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Numerical simulations supplemented by experiments together uncovered that strategic integration of discrete electric fields in a non-invasive manner could substantially miniaturize the droplets into smaller parts in a pressure driven oil-water flow inside microchannels. The Maxwell's stress generated from the electric field at the oil-water interface could deform, stretch, neck, pin, and disintegrate a droplet into many miniaturized daughter droplets, which eventually ushered a one-step method to form water-in-oil microemulsion employing microchannels. The interplay between electrostatic, inertial, capillary, and viscous forces led to various pathways of droplet breaking, namely, fission, cascade, or Rayleigh modes. While a localized electric field in the fission mode could split a droplet into a number of daughter droplets of smaller size, the cascade or the Rayleigh mode led to the formation of an array of miniaturized droplets when multiple electrodes generating different field intensities were ingeniously assembled around the microchannel. The droplets size and frequency could be tuned by varying the field intensity, channel diameter, electrode locations, interfacial tension, and flow ratio. The proposed methodology shows a simple methodology to transform a microdroplet into an array of miniaturized ones inside a straight microchannel for enhanced mass, energy, and momentum transfer, and higher throughput.

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Self-Organized Ordered Arrays of Core−Shell Columns in Viscous Bilayers Formed by Spatially Varying Electric Fields

Cited by 30 publications

References 131 publications

Localized electric field induced transition and miniaturization of two‐phase flow patterns inside microchannels

Localized electric field induced transition and miniaturization of two‐phase flow patterns inside microchannels

Electrohydrodynamic patterning of ultra-thin ionic liquid films

Discrete electric field mediated droplet splitting in microchannels: Fission, Cascade, and Rayleigh modes

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