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Raju G, Kyriakopoulos N, Timonen JVI. Diversity of non-equilibrium patterns and emergence of activity in confined electrohydrodynamically driven liquids. SCIENCE ADVANCES 2021; 7:eabh1642. [PMID: 34524853 PMCID: PMC8443174 DOI: 10.1126/sciadv.abh1642] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 07/23/2021] [Indexed: 05/31/2023]
Abstract
Spontaneous emergence of organized states in materials driven by non-equilibrium conditions is of notable fundamental and technological interest. In many cases, the states are complex, and their emergence is challenging to predict. Here, we show that an unexpectedly diverse collection of dissipative organized states emerges in a simple system of two liquids under planar confinement when driven by electrohydrodynamic shearing. At low shearing, a symmetry breaking at the liquid-liquid interface leads to a one-dimensional corrugation pattern. At slightly stronger shearing, topological changes give raise to the emergence of Quincke rolling filaments, filament networks, and two-dimensional bicontinuous fluidic lattices. At strong shearing, the system transitions into dissipating polygonal, toroidal, and active droplets that form dilute gas-like states at low densities and complex active emulsions at higher densities. The diversity of the observed dissipative organized states is exceptional, pointing toward non-equilibrium optical devices and new avenues in several fields of research.
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Huang X, He L, Luo X, Xu K, Lü Y, Yang D. Coalescence, Partial Coalescence, and Noncoalescence of Two Free Droplets Suspended in Low-Viscosity Oil under a DC Electric Field. J Phys Chem B 2020; 124:7508-7517. [PMID: 32790395 DOI: 10.1021/acs.jpcb.0c05371] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Enhancing the electric field strength can facilitate the approach of droplets and the drainage of liquid film. However, two droplets do not coalesce but bounce off after contact under an excessively high electric field strength. To reveal the underlying mechanism, the dynamic behaviors of two free droplets suspended in low-viscosity silicone oil under a DC electric field were investigated herein. Three distinct behavior modes were successively observed by a high-speed camera with the increase in electric field strength: coalescence, partial coalescence, and noncoalescence. The mechanisms and key criteria of partial coalescence and noncoalescence were explored by studying the competition between electric force and interfacial force. The theoretical formula of critical electric field strength for droplet coalescence was derived and validated by experiments. The results indicated that the electric capillary number Ca can be used as the criterion to identify the behavior modes of two free droplets. The droplets undergo partial coalescence or noncoalescence when Ca > 0.11; otherwise, the droplets experience coalescence.
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Affiliation(s)
- Xin Huang
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
| | - Limin He
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
| | - Xiaoming Luo
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
| | - Ke Xu
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
| | - Yuling Lü
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
| | - Donghai Yang
- College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao 266580, PR China
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Abbasi MS, Song R, Lee J. Breakups of an encapsulated surfactant-laden aqueous droplet under a DC electric field. SOFT MATTER 2019; 15:8905-8911. [PMID: 31621746 DOI: 10.1039/c9sm01623f] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
We investigate the breakups of an encapsulated conducting aqueous droplet under a direct-current electric field via extensive experiments and theoretical analysis. The encapsulating shell phase and the ambient phase consist of leaky dielectric liquids. We change the surface tension by using an aqueous core with different surfactant (Tween 80) concentrations. Moreover, we vary the core size under different electric-field conditions and observe the core dynamics. We present three different breakup modes of the encapsulated droplet. In the first mode, the encapsulated core forms asymmetric Janus shapes after breakup. In the second and third breakup modes, stable and unstable ternary droplets are formed, respectively. We show that the surfactant molecules significantly alter the dynamics of core stretching. According to the theoretical analysis, we identify the critical conditions of instability leading to breakup. We plot the breakup modes in the form of a phase diagram in the electric capillary number (Ca23 = ε3rsEo2/γ23; ratio of interfacial electric to capillary stresses) vs. radius ratio of the core to the shell (β = rc/rs) parametric space at different nondimensional surfactant concentrations (C* = CTween 80/CCMC, where CCMC represents the critical micellar concentration). The study provides essential physical insight into encapsulated emulsions and is useful for their application in various areas of science and technology.
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Affiliation(s)
- Muhammad Salman Abbasi
- School of Mechanical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea. and Faculty of Mechanical Engineering, University of Engineering and Technology, Lahore, Pakistan
| | - Ryungeun Song
- School of Mechanical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea.
| | - Jinkee Lee
- School of Mechanical Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea.
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Luo X, Yin H, Yan H, Huang X, Yang D, He L. The electrocoalescence behavior of surfactant-laden droplet pairs in oil under a DC electric field. Chem Eng Sci 2018. [DOI: 10.1016/j.ces.2018.07.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Tadavani SK, Yethiraj A. Anomalous dynamics in tracer-particle motions in an electrohydrodynamically driven oil-in-oil system. Phys Rev E 2018; 98:022602. [PMID: 30253573 DOI: 10.1103/physreve.98.022602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Indexed: 11/07/2022]
Abstract
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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Affiliation(s)
- Somayeh Khajehpour Tadavani
- Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3X7 Canada
| | - Anand Yethiraj
- Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland, A1B 3X7 Canada
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Luo X, Huang X, Yan H, Yang D, Wang J, He L. Breakup modes and criterion of droplet with surfactant under direct current electric field. Chem Eng Res Des 2018. [DOI: 10.1016/j.cherd.2018.02.033] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
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Cortés-Domínguez I, Burguete J. Instabilities of conducting fluid layers in weak time-dependent magnetic fields. Phys Rev E 2018; 96:013103. [PMID: 29347070 DOI: 10.1103/physreve.96.013103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Indexed: 11/07/2022]
Abstract
We present the experimental analysis of the instabilities generated on a large drop of liquid metal by a time-dependent magnetic field. The study is done exploring the range of tiny values of the control parameter (the ratio between the Lorentz forces and inertia) avoiding nonlinear effects. Two different instabilities break the symmetries generating spatial patterns that appear without a threshold for some specific frequencies (up to the experimental precision) and have been observed for parameter values two orders of magnitude lower than in previously published experiments [J. Fluid Mech. 239, 383 (1992)JFLSA70022-112010.1017/S0022112092004452]. One of the instabilities corresponds to a boundary condition oscillation that generates surface waves and breaks the azimuthal symmetry. The other corresponds to a parametric forcing through a modulation of the Lorentz force. The competition between these two mechanisms produces time-dependent patterns near codimension-2 points.
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Affiliation(s)
- I Cortés-Domínguez
- Departamento de Física y Matemática Aplicada, Facultad de Ciencias, Universidad de Navarra, Navarra, Spain
| | - J Burguete
- Departamento de Física y Matemática Aplicada, Facultad de Ciencias, Universidad de Navarra, Navarra, Spain
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Breakup characteristics of aqueous droplet with surfactant in oil under direct current electric field. J Colloid Interface Sci 2017. [DOI: 10.1016/j.jcis.2017.06.042] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Khajehpour Tadavani S, Yethiraj A. Tunable hydrodynamics: a field-frequency phase diagram of a non-equilibrium order-to-disorder transition. SOFT MATTER 2017; 13:7412-7424. [PMID: 28960017 DOI: 10.1039/c7sm01145h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
We present experiments on a model system consisting of dielectric (silicone oil) drops in a "leaky dielectric" (castor oil) carrier fluid that exhibits dynamic non-equilibrium phases as a function of the amplitude and frequency of an external AC electric field. At high frequencies, the dielectric drops are pinned to a periodic lattice by dielectrophoretic forces induced by a patterned bottom electrode. Beginning with this state of imposed order, we examine the processes that take this system from order to disorder, with decreasing frequency corresponding to an increase in the range of the hydrodynamic forces. We find two kinds of disorder, shape- and translational disorder, that occur in frequency-amplitude space. We also find regimes where drop breakup is dominant, and where order/disorder of large drops can be probed without significant drop breakup. With decreasing frequency (i.e., increasing hydrodynamic coupling between drops) and on timescales from seconds to minutes, the drops exhibit motion that resembles Brownian motion of particles in a crystal, with an effective temperature that increases with the strength of the electrohydrodynamic driving force. In this limit, the system behaves like a thermal system and the lattice is seen to melt at an effective Lindemann parameter of Leff ∼ 0.08. This non-equilibrium thermodynamics, probed on timescales from seconds to minutes, likely arises from the pseudo-random velocity fields in the carrier fluid, as evidenced by the fractional, t3/2, super-diffusive tracer dynamics at shorter timescales.
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Tadavani SK, Munroe JR, Yethiraj A. The effect of confinement on the electrohydrodynamic behavior of droplets in a microfluidic oil-in-oil emulsion. SOFT MATTER 2016; 12:9246-9255. [PMID: 27801470 DOI: 10.1039/c6sm01648k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
A two-fluid emulsion (silicone oil drops in the "leaky dielectric", castor oil) with electrohydrodynamically driven flows can serve as a model system for tunable studies of hydrodynamic interactions [Varshney et al., Sci. Rep., 2012, 2, 738]. Flows on multiple length- and time-scales have been observed but the underlying mechanism for these chaotic, multi-scale flows is not understood. In this work, we conducted experiments varying the thickness of the test cell to examine the role of substrate interactions on size distribution, mean square displacement and velocity of the drops as a function of the electric field strength. We find that the electric capillary number, CaE, at the threshold of drop breakup is of order unity for cell thicknesses of 100 μm or thicker, but much larger for thinner cells. Above this threshold, there is a clear transition to super-diffusive droplet motions. In addition, we observe that there is a convective instability prior to the onset of chaotic flows, with the lengthscale associated with the convection rolls increasing linearly with an increase in the cell thickness. The fact that the convective instability appears to occur in the leaky dielectric castor oil regardless of whether the second component is liquid drops, solid particles, or dissolved dye has implications on the underlying mechanism for the unsteady flows.
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Affiliation(s)
| | - James R Munroe
- Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL A1B 3X7, Canada.
| | - Anand Yethiraj
- Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL A1B 3X7, Canada.
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Varshney A, Gohil S, Sathe M, R V SR, Joshi JB, Bhattacharya S, Yethiraj A, Ghosh S. Multiscale flow in an electro-hydrodynamically driven oil-in-oil emulsion. SOFT MATTER 2016; 12:1759-1764. [PMID: 26693675 DOI: 10.1039/c5sm02316e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Efficient mixing strategies in a fluid involve generation of multi-scale flows which are strongly suppressed in highly viscous systems. In this work, we report a novel form of multi-scale flow, driven by an external electric field, in a highly viscous (η∼ 1 Pa s) oil-in-oil emulsion system consisting of micron-size droplets. This electro-hydrodynamic flow leads to dynamical organization at spatial scales much larger than that of the individual droplets. We characterize the dynamics associated with these structures by measuring the time variation of the bulk Reynolds stress in a rheometer, as well as through a micro-scale rheometric measurement by probing the spectrum of fluctuations of a thin fiber cantilever driven by these flows. The results display scale invariance in the energy spectra over three decades with a power law reminiscent of turbulent convection. We also demonstrate the mixing efficiency in such micro-scale systems.
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Affiliation(s)
- Atul Varshney
- Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel.
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Karyappa RB, Thaokar RM. Electric-field-assisted formation of nonspherical microcapsules. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:10270-10279. [PMID: 25010595 DOI: 10.1021/la501617t] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A new method for studying the effect of pH on the polysiloxane network formation using electric fields is presented. The kinetic data obtained using these experiments indicates that the two-step interfacial polycondensation of silanes is strongly dependent on the pH, and the mechanism is essentially different at low and neutral to high values of pH. Very rapid hydrolysis followed by moderate rates of condensation are observed at neutral and high pH. The rate of hydrolysis is drastically reduced, while that of condensation is slightly lowered at low pH as compared to that at high values of pH. The slow hydrolysis reaction at low pH is then exploited to synthesize nonspherical microcapsules. Nonspherical polysiloxane microcapsules with varying aspect ratios from 1.05to 1.97 are synthesized by controlling the applied electric field.
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Affiliation(s)
- Rahul B Karyappa
- Department of Chemical Engineering, Indian Institute of Technology Bombay , Powai, Mumbai 400 076, India
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Varshney A, Gohil S, Tadavani SK, Yethiraj A, Bhattacharya S, Ghosh S. Large scale arrays of tunable microlenses. LAB ON A CHIP 2014; 14:1330-1335. [PMID: 24519377 DOI: 10.1039/c3lc51170g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We demonstrate a simple and robust method to produce large 2-dimensional and quasi-3-dimensional arrays of tunable liquid microlenses using a time varying external electric field as the only control parameter. With increasing frequency, the shape of the individual lensing elements (~40 μm in diameter) evolves from an oblate (lentil shaped) to a prolate (egg shaped) spheroid, thereby making the focal length a tunable quantity. Moreover, such microlenses can be spatially localized in desired configurations by patterning the electrode. This system has the advantage that it provides a large dynamic range of shape deformation (with a response time of ~30 ms for the whole range of deformation), which is useful in designing adaptive optics.
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Affiliation(s)
- Atul Varshney
- Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400-005, India.
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