Electrohydrodynamics: A Review of the Role of Interfacial Shear Stresses

Melcher, James R.; Taylor, G. I.

doi:10.1146/annurev.fl.01.010169.000551

Cited by 1,126 publications

(843 citation statements)

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“…Due to the possible rotation of the particle, both ohmic conduction and charge advection contribute to the surface current: j s = σE + q s Ω × ar. After some elementary algebra, the charge-conservation equation can be recast into a dynamical equation for the dipole moment P [27,28]:…”

Section: From Quincke Rotation To Self-propulsion: the Single Rollmentioning

confidence: 99%

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Emergence of macroscopic directed motion in populations of motile colloids

Bricard¹,

Caussin²,

Desreumaux³

et al. 2013

Nature

868

1,029

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From the formation of animal flocks to the emergence of coordinate motion in bacterial swarms, at all scales, populations of motile organisms display coherent collective motion.This consistent behavior strongly contrasts with the difference in communication abilities between the individuals. Guided by this universal feature, physicists have proposed that solely alignment rules at the individual level could account for the emergence of unidirectional motion at the group level [1][2][3][4] . This hypothesis has been supported by agent-based simulations 1,5,6 . However, more complex collective behaviors have been systematically found in experiments including the formation of vortices 7-9 , fluctuating swarms 7, 10 , clustering 11,12 , and swirling [13][14][15][16] . All these (living and man-made) model systems (bacteria 9,10, 16 , biofilaments and molecular motors 7,8,13 , shaken grains 14, 15 and reactive colloids 11,12 ) predominantly rely on actual collisions to display collective motion. As a result, the potential local alignment rules are entangled with more complex, and often unknown, interactions. The large-scale behaviour of the populations therefore strongly depends on these uncontrolled microscopic couplings that are extremely challenging to measure and describe theoretically.Here, we demonstrate a new phase of active matter. We reveal that dilute populations of millions of colloidal rollers self-organize to achieve coherent motion along a unique direction, with very few density and velocity fluctuations. Identifying, quantitatively, the microscopic interactions between the rollers allows a theoretical description of this polar-liquid state. Comparison of the theory with experiment suggests that hydrodynamic interactions promote the emergence of collective motion either in the form of a single macroscopic flock at low densities, or in that of a homogenous polar phase at higher densities. Furthermore, hydrodynamics protects the polar-liquid state from the giant density fluctuations, which were hitherto considered as the hallmark of populations of self-propelled particles 2, 3, 17 . Our experiments demonstrate that genuine physical interactions at the individual level are sufficient to set homogeneous active populations into stable directed motion.Our system consists of large populations of colloids capable of self-propulsion and of sensing the orientation of their neighbors solely by means of physical mechanisms. We take advantage of an overlooked electrohydrodynamic phenomenon referred to as the Quincke rotation 18,19 (Fig. 1a).When an electric field E 0 is applied to an insulating sphere immersed in a conducting fluid, above a critical field amplitude E Q , the charge distribution at the sphere's surface is unstable to infinitesimal fluctuations. This spontaneous symmetry breaking results in a net electrostatic torque, which causes the sphere to rotate at a constant speed around a random direction transverse to E 0 18 . We 2 exploit this instability to engineer self-propelled colloidal rollers. We use ...

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Section: From Quincke Rotation To Self-propulsion: the Single Rollmentioning

confidence: 99%

“…We take advantage of an overlooked electrohydrodynamic phenomenon referred to as the Quincke rotation 18,19 (Fig. 1a).…”

mentioning

confidence: 99%

Emergence of macroscopic directed motion in populations of motile colloids

Bricard¹,

Caussin²,

Desreumaux³

et al. 2013

Nature

868

1,029

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“…Mass transport out of the locally polarized region, driven both by the gradients in density and chemical potential is further accelerated by electrokinetic forces arising at interfaces in the system. 65 In addition to the air-water interface an internal dynamical surface is also present. This surface is defined by how far the electric field gradient extends in the liquids with a magnitude greater than the dissipative energies of the bulk which are proportional to both the temperature and any shear forces present.…”

Section: The Effect Of Exciting a Delocalized Vibrational Statementioning

confidence: 99%

Non-equilibrium thermodynamics and collective vibrational modes of liquid water in an inhomogeneous electric field

Wexler¹,

Drusová²,

Woisetschläger

et al. 2016

Phys. Chem. Chem. Phys.

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“…Specifically, the charge relaxation process is nearly instantaneous for electrolytes and is neglected, and molecular diffusion becomes very important in the microscale regime and is included. In Melcher (1981), two approaches were adopted in deriving the Ohmic model: one approach is based on conservation laws of bulk properties including charge density and electrical conductivity (Melcher & Taylor 1969); the other approach starts from the electro-diffusion equations of individual species which incorporates the Nernst-Plank equations for charged ions (Levich 1962). A proper modification of the Ohmic model for electrokinetic microsystems can be shown using either approach.…”

Section: Introductionmentioning

confidence: 99%

Convective and absolute electrokinetic instability with conductivity gradients

et al. 2005

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Electrokinetic flow instabilities occur under high electric fields in the presence of electrical conductivity gradients. Such instabilities are a key factor limiting the robust performance of complex electrokinetic bio-analytical systems, but can also be exploited for rapid mixing and flow control for microscale devices. This paper reports a representative flow instability phenomenon studied using a microfluidic T-junction with a cross-section of 11 µm by 155 µm. In this system, aqueous electrolytes of 10:1 conductivity ratio were electrokinetically driven into a common mixing channel by a steady electric field. Convectively unstable waves were observed with a nominal threshold field of 0.5 kV cm −1 , and upstream propagating waves were observed at 1.5 kV cm −1 . A physical model has been developed for this instability which captures the coupling between electric and flow fields. A linear stability analysis was performed on the governing equations in the thin-layer limit, and Briggs-Bers criteria were applied to select physically unstable modes and determine the nature of instability. The model predicts both qualitative trends and quantitative features that agree very well with experimental data, and shows that conductivity gradients and their associated bulk charge accumulation are crucial for such instabilities. Comparison between theory and experiments suggests the convective role of electro-osmotic flow. Scaling analysis and numerical results show that the instability is governed by two key controlling parameters: the ratio of dynamic to dissipative forces which governs the onset of instability, and the ratio of electroviscous to electro-osmotic velocities which governs the convective versus absolute nature of instability.

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Electrohydrodynamics: A Review of the Role of Interfacial Shear Stresses

Cited by 1,126 publications

References 0 publications

Emergence of macroscopic directed motion in populations of motile colloids

Emergence of macroscopic directed motion in populations of motile colloids

Non-equilibrium thermodynamics and collective vibrational modes of liquid water in an inhomogeneous electric field

Convective and absolute electrokinetic instability with conductivity gradients

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