Non-equilibrium electric surface phenomena

Dukhin, S. S.

doi:10.1016/0001-8686(93)80021-3

Cited by 302 publications

(264 citation statements)

References 101 publications

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“…Nonlinear electrophoretic effects discussed in ref. [31][32][33][34] are negligible at these conditions. We tracked the center of mass position of 25 beads.…”

Section: Field Characterizationmentioning

confidence: 87%

Methods to electrophoretically stretch DNA: microcontractions, gels, and hybrid gel-microcontraction devices

2006

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“…Nonlinear electrophoretic effects discussed in ref. [31][32][33][34] are negligible at these conditions. We tracked the center of mass position of 25 beads.…”

Section: Field Characterizationmentioning

confidence: 87%

Methods to electrophoretically stretch DNA: microcontractions, gels, and hybrid gel-microcontraction devices

2006

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“…In general, more attention was given to the induced dipole moment and its effect on dielectrophoresis rather than the associated electrokinetic flows in polarizable colloids (Dukhin & Shilov 1974, 1980. All of these studies fit into the larger context of 'non-equilibrium electro-surface phenomena' in colloids, studied extensively in the Soviet Union since the 1960s (Dukhin 1993). This work deserves renewed attention from the perspective of designing colloids and microfluidic devices, since geometrical complexity (the focus of this paper) can now be engineered to control flows and particle motions, in ways not anticipated by the many earlier studies of ideal colloidal spheres.…”

Section: Introductionmentioning

confidence: 99%

Breaking symmetries in induced-charge electro-osmosis and electrophoresis

2006

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Building on our recent work on induced-charge electro-osmosis (ICEO) and electrophoresis (ICEP), as well as the Russian literature on spherical metal colloids, we examine the rich consequences of broken geometric and field symmetries upon the ICEO flow around conducting bodies. Through a variety of paradigmatic examples involving ideally polarizable (e.g. metal) bodies with thin double layers in weak fields, we demonstrate that spatial asymmetry generally leads to a net pumping of fluid past the body by ICEO, or, in the case of a freely suspended colloidal particle, translation and/or rotation by ICEP. We have chosen model systems that are simple enough to admit analysis, yet which contain the most important broken symmetries. Specifically, we consider (i) symmetrically shaped bodies with inhomogeneous surface properties, (ii) 'nearly symmetric' shapes (using a boundary perturbation scheme), (iii) highly asymmetric bodies composed of two symmetric bodies tethered together, (iv) symmetric conductors in electric-field gradients, and (v) arbitrarily shaped conductors in general non-uniform fields in two dimensions (using complex analysis). In non-uniform fields, ICEO flow and ICEP motion exist in addition to the more familiar dielectrophoretic forces and torques on the bodies (which also vary with the square of the electric field). We treat all of these problems in two and three dimensions, so our study has relevence for both colloids and microfluidics. In the colloidal context, we describe principles to 'design' polarizable particles which rotate to orient themselves and translate steadily in a desired direction in a DC or AC electric field. We also describe 'ICEO spinners' that rotate continuously in AC fields of arbitrary direction, although we show that 'near spheres' with small helical perturbations do not rotate, to leading order in the shape perturbation. In the microfluidic context, strong and steady flows can be driven by small AC potentials applied to systems containing asymmetric structures, which holds promise for portable or implantable self-powered devices. These results build upon and generalize recent studies in AC electro-osmosis (ACEO). Unlike ACEO, however, the inducing surfaces in ICEO can be physically distinct from the driving electrodes, increasing the frequency range and geometries available.

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“…In that case, the maximum frequency, ω c , is of order 10 kHz for λ D = 10nm. (For these parameters, we are also justified in neglecting surface conduction [3,13].) The symmetry of ICEO flow in Fig.…”

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confidence: 99%

“…NESP mostly involve steady surface conduction, n · J = −∇ s · J s , at low AC frequencies, ω ≪ D/a 2 , which produces concentration gradients affecting electroosmosis at highly charged surfaces [11,13]. In contrast, ICEO derives from the dominant "RC coupling" for small ζ (initial + induced) in a homogeneous electrolyte:…”

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confidence: 99%

Induced-Charge Electrokinetic Phenomena: Theory and Microfluidic Applications

2004

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We give a general, physical description of "induced-charge electro-osmosis" (ICEO), the nonlinear electrokinetic slip at a polarizable surface, in the context of some new techniques for microfluidic pumping and mixing. ICEO generalizes "AC electro-osmosis" at micro-electrode arrays to various dielectric and conducting structures in weak DC or AC electric fields. The basic effect produces micro-vortices to enhance mixing in microfluidic devices, while various broken symmetries -controlled potential, irregular shape, non-uniform surface properties, and field gradients -can be exploited to produce streaming flows. Although we emphasize the qualitative picture of ICEO, we also briefly describe the mathematical theory (for thin double layers and weak fields) and apply it to a metal cylinder with a dielectric coating in a suddenly applied DC field.The advent of microfluidic technology raises the fundamental question of how to pump and mix fluids at micron scales, where pressure-driven flows and inertial instabilities are suppressed by viscosity [1,2]. The most popular non-mechanical pumping strategy is based on electro-osmosis -the effective slip, u , at a liquidelectrolyte/solid interface due to tangential electric field, E . The Helmholtz-Smoluchowski formula,gives the slip in terms of the permittivity, ε, and viscosity, η, of the liquid and the zeta potential, ζ, across the diffuse part of the (thin) interfacial double layer [3]. The usual case of constant (possibly non-uniform [4]) ζ, however, has some drawbacks related to linearity, u ∝ E : (i) the flow is somewhat weak, e.g. u = 70µm/s in aqueous solution with E = 100 V/cm and ζ = 10 mV and (ii) AC fields, which reduce undesirable Faradaic reactions, produce zero time-averaged flow. These drawbacks do not apply to AC electro-osmosis, recently discovered by Ramos et al. [5] and Ajdari [6]. Nonlinear electro-osmotic slip is produced at microelectrodes as an AC field acts on induced double-layer charge prior to complete screening. In spite of extensive work, however, this promising effect remains limited to quasi-planar pairs [7] or arrays [8] of electrodes at a single AC frequency, ω c = τ −1 c , where τ c = λ D L/D is the "RC time" of an equivalent circuit of bulk resistors of size L (the electrode spacing) and double-layer capacitors of thickness, λ D , the Debye screening length, and D is an ionic diffusivity.How general is this phenomenon? Nonlinear electroosmotic flows have also been observed at dielectric impurities on electrodes with AC forcing [9] and, more suggestively, at dielectric (non-electrode) micro-channel corners in DC fields [10]. Although it is largely unknown (and uncited) in the West, similar flows have also been studied in the Russian literature on polarizable colloids [11], including the effect of such flows on dielectrophoresis [12]. The unifying principle in these diverse effects is that an applied field acts on its own induced diffuse charge, so we suggest the term, "induced-charge electro-osmosis" (ICEO), to describe it.In this Letter, w...

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Non-equilibrium electric surface phenomena

Cited by 302 publications

References 101 publications

Methods to electrophoretically stretch DNA: microcontractions, gels, and hybrid gel-microcontraction devices

Methods to electrophoretically stretch DNA: microcontractions, gels, and hybrid gel-microcontraction devices

Breaking symmetries in induced-charge electro-osmosis and electrophoresis

Induced-Charge Electrokinetic Phenomena: Theory and Microfluidic Applications

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