Effect of the difference in ion mobilities on traveling-wave electro-osmosis

Electro-osmosis on anisotropic super-hydrophobic surfaces

We give a general theoretical description of electro-osmotic flow at striped super-hydrophobic surfaces in a thin double layer limit, and derive a relation between the electro-osmotic mobility and hydrodynamic slip-length tensors. Our analysis demonstrates that electro-osmotic flow shows a very rich behavior controlled by slip length and charge at the gas sectors. In case of uncharged liquid-gas interface, the flow is the same or inhibited relative to flow in homogeneous channel with zero interfacial slip. By contrast, it can be amplified by several orders of magnitude provided slip regions ar…

Induced-Charge Electro-Osmosis

We describe the general phenomenon of `induced-charge electro-osmosis' (ICEO) -- the nonlinear electro-osmotic slip that occurs when an applied field acts on the ionic charge it {\sl induces} around a polarizable surface. Motivated by a simple physical picture, we calculate ICEO flows around conducting cylinders in steady (DC), oscillatory (AC), and suddenly-applied electric fields. This picture, and these systems, represent perhaps the clearest example of nonlinear electrokinetic phenomena. We complement and verify this physically-motivated approach using a matched asymptotic expansion to the…

Equilibrium Electro-osmotic Instability

Since its prediction fifteen years ago, electro-osmotic instability has been attributed to non-equilibrium electro-osmosis related to the extended space charge which develops at the limiting current in the course of concentration polarization at a charge-selective interface. This attribution had a double basis. Firstly, it has been recognized that equilibrium electro-osmosis cannot yield instability for a perfectly charge-selective solid. Secondly, it has been shown that non-equilibrium electro-osmosis can. First theoretical studies in which electro-osmotic instability was predicted and analyz…

Induced-charge Electrokinetic Phenomena: Theory and Microfluidic Applications

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 t…

Effect of Induced-Charge Electro-Kinetics on Concentration-Polarization in a Microchannel-Nafion System

Induced-charge electro-osmosis (ICEO) is shown to control the length scale of the diffusion layer (DL), which in turn, affects the diffusion limited ion transport through the microchannel-Nafion membrane system. The ICEO vortices form at an interdigitated floating electrode array embedded within a microchannel interfacing a Nafion membrane and stir the fluid, arresting the diffusive growth of the depletion layer. By varying the spacing between the array and the membrane we are able to control the length of the DL. Activating the electrodes results in further enhancement of the fluid stirring d…

由表面离子迁移率引起的增强的zeta电势

Enhanced zeta potentials caused by surface ion mobilities

本文研究了导电壁附近扩散Stern层对电渗流的影响，提出有效滑移边界条件并引入迁移率参数$μ$，导出其解析方程，发现zeta电势通常超过表面电势从而放大电渗流。

Electro-osmotic Instability of Concentration Enrichment in Curved Geometries for an Aqueous Electrolyte

We report that an electro-osmotic instability of concentration enrichment in curved geometries for an aqueous electrolyte, as opposed to the well-known one, is initiated exclusively at the enriched interface (anode), rather than at the depleted one (cathode). For this instability, the limitation of unrealistically high material Peclet number in planar geometry is eliminated by the strong electric field arising from the line charge singularity. In a model setup of concentric circular electrodes, we show by stability analysis, numerical simulation, and experimental visualization that instability…

Modeling Electrokinetic Flows with the Discrete Ion Stochastic Continuum Overdamped Solvent Algorithm

In this article we develop an algorithm for the efficient simulation of electrolytes in the presence of physical boundaries. In previous work the Discrete Ion Stochastic Continuum Overdamped Solvent (DISCOS) algorithm was derived for triply periodic domains, and was validated through ion-ion pair correlation functions and Debye-H{ü}ckel-Onsager theory for conductivity, including the Wien effect for strong electric fields. In extending this approach to include an accurate treatment of physical boundaries we must address several important issues. First, the modifications to the spreading and int…