The effect of confinement on the electrohydrodynamic behavior of droplets in a microfluidic oil-in-oil emulsion

Tadavani, Somayeh Khajehpour; Munroe, James; Yethiraj, Anand

doi:10.1039/c6sm01648k

Cited by 14 publications

(9 citation statements)

References 34 publications

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“…O/o emulsions are typically prepared by adding one oil phase to the other containing the stabilizer followed by vortex, sonication, or homogenization. − In recent years, emphasis has been placed on the emulsification technique used to prepare nonaqueous emulsions. Besides commonly applied mechanical stirring and ultrasonic homogenization, microfluidics , and the application of electric fields have emerged as powerful methods for the fabrication of o/o emulsions with narrow size distributions. The continuous and dispersed phases for o/o emulsions are selected on the basis of the desired application, with the volume fractions of both phases, and the weight-to-volume ratio of the stabilizers being varied to identify optimal conditions, which are often empirically found.…”

Section: Introductionmentioning

confidence: 99%

Advances and Opportunities of Oil-in-Oil Emulsions

Zia

Pentzer

Thickett

et al. 2020

ACS Appl. Mater. Interfaces

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Emulsions are mixtures of two immiscible liquids in which droplets of one are dispersed in a continuous phase of the other. The most common emulsions are oil–water systems, which have found widespread use across a number of industries, for example, in the cosmetic and food industries, and are also of advanced scientific interest. In addition, the past decade has seen a significant increase in both the design and application of nonaqueous emulsions. This has been primarily driven by developments in understanding the mechanism of effective stabilization of oil-in-oil (o/o) systems, either using block copolymers (BCPs) or solid (Pickering) particles with appropriate surface functionality. These systems, as highlighted in this review, have enabled emergent applications in areas such as pharmaceutical delivery, energy storage, and materials design (e.g., polymerization, monolith, and porous polymer synthesis). These o/o emulsions complement traditional emulsions that utilize an aqueous phase and allow the use of materials incompatible with water. We assess recent advances in the preparation and stabilization of o/o emulsions, focusing on the identity of the stabilizer (BCP or particle), the interplay between stabilizer and oils, and highlighting applications and opportunities associated with o/o emulsions.

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Section: Introductionmentioning

confidence: 99%

Advances and Opportunities of Oil-in-Oil Emulsions

Zia

Pentzer

Thickett

et al. 2020

ACS Appl. Mater. Interfaces

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“…Micromodels are particularly useful laboratory tools for direct visualization and quantitative description of pore-scale mechanisms controlling the flow and transport phenomena in subsurface porous rocks with micrometer pores and throats. As such, microfluidics have been used to study the flow dynamics and transport properties in porous media that may involve single phase flow of Newtonian and non-Newtonian fluids, multiphase flow, − droplet formation/coalescence, − and physicochemical interactions at the fluid–matrix interface. − Despite this, the potential of microfluidics to study the dynamical behavior of water–oil–amphiphile(s) mixtures that form microemulsions is relatively unexplored. Unsal et al coinjected n -decane and an aqueous solution of olefin sulfonate surfactant in a T -junction capillary geometry to compare the equilibrium and dynamic phase behaviors of the mixture when the phase environment is Type-I–III–II .…”

Section: Introductionmentioning

confidence: 99%

Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale

Tagavifar

Jang

et al. 2017

Langmuir

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The dynamic behavior of microemulsion-forming water-oil-amphiphiles mixtures is investigated in a 2.5D micromodel. The equilibrium phase behavior of such mixtures is well-understood in terms of macroscopic phase transitions. However, what is less understood and where experimental data are lacking is the coupling between the phase change and the bulk flow. Herein, we study the flow of an aqueous surfactant solution-oil mixture in porous media and analyze the dependence of phase formation and spatial phase configurations on the bulk flow rate. We find that a microemulsion forms instantaneously as a boundary layer at the initial surface of contact between the surfactant solution and oil. The boundary layer is temporally continuous because of the imposed convection. In addition to the imposed flow, we observe spontaneous pulsed Marangoni flows that drag the microemulsion and surfactant solution into the oil stream, forming large (macro)emulsion droplets. The formation of the microemulsion phase at the interface distinguishes the situation from that of the more common Marangoni flow with only two phases present. Additionally, an emulsion forms via liquid-liquid nucleation or the Ouzo effect (i.e., spontaneous emulsification) at low flow rates and via mechanical mixing at high flow rates. With regard to multiphase flow, contrary to the common belief that the microemulsion is the wetting liquid, we observe that the minor oil phase wets the solid surface. We show that a layered flow pattern is formed because of the out-of-equilibrium phase behavior at high volumetric flow rates (order of 2 m/day) where advection is much faster than the diffusive interfacial mass transfer and transverse mixing, which promote equilibrium behavior. At lower flow rates (order of 30 cm/day), however, the dynamic and equilibrium phase behaviors are well-correlated. These results clearly show that the phase change influences the macroscale flow behavior.

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“…At very low frequency, in the regime of strong hydrodynamics where the hydrodynamic length, l h , is on the order of hundreds of micrometers [25], large silicone oil drops are broken into many tiny droplets vigorously. The spontaneous breakup of droplets is a result of overcoming the viscous stresses by electric stresses at the interface of the droplets [24,[28][29][30]. The strong inhomogeneous flows, with breakup accompanied by coalescence, can be achieved by either lowering the frequency or increasing the field amplitude.…”

Section: Pattern Formation and Flow Visualizationmentioning

confidence: 99%

Anomalous dynamics in tracer-particle motions in an electrohydrodynamically driven oil-in-oil system

Tadavani

Yethiraj

2018

Phys. Rev. E

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We characterize the superdiffusive dynamics of tracer particles in an electrohydrodynamically driven emulsion of oil droplets in an immiscible oil medium, where the amplitude and frequency of an external electric field are the control parameters. In the weakly driven electrohydrodynamic regime, the droplets are trapped dielectrophoretically on a patterned electrode, and the driving is therefore spatially varying. We find excellent agreement with a 〈x^{2}〉∼t^{1.5} power law and find that this superdiffusive dynamics arises from an underlying displacement distribution that is distinctly non-Gaussian and exponential for small displacements and short times. While these results are comparable with a random-velocity field model, the tracer particle speeds are in fact spatially varying in two dimensions, arising from a spatially varying electrohydrodynamic driving force. This suggests that the important ingredient for the superdiffusive t^{1.5} behavior observed is a velocity field that is isotropic in the plane and spatially correlated. Finally, we can extract, from the superdiffusive dynamics, a experimental length scale that corresponds to the lateral range of the hydrodynamic flows. This experimental length scale is non zero only above a threshold ion mobility length.

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The effect of confinement on the electrohydrodynamic behavior of droplets in a microfluidic oil-in-oil emulsion

Cited by 14 publications

References 34 publications

Advances and Opportunities of Oil-in-Oil Emulsions

Advances and Opportunities of Oil-in-Oil Emulsions

Spontaneous and Flow-Driven Interfacial Phase Change: Dynamics of Microemulsion Formation at the Pore Scale

Anomalous dynamics in tracer-particle motions in an electrohydrodynamically driven oil-in-oil system

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