Induced-Charge Electrokinetic Flow

Induced-Charge Electrokinetic Flow, Fig. 2 Schematic of a microchannel... 

Induced-Charge Electrokinetic Flow, Fig. 3 Induced double layer on the surface of a polarized sphere when subjected to a uniform electric field... 

Wu Z, Li D (2008) Mixing and flow regulating by induced-charge electrokinetic flow in a micrtKhannel with a pair of conducting triangle hurdles. Microfluid Nanofluid 5 65—76... 

Wu Z, li D (2008) Micromixing using induced-charge electrokinetic flow. Electr(Khim Acta 53 5827-5835... 

Induced-Charge Electrokinetic Motion of Particle in a MicroChannel, Fig. 2 Induced-charge electrokinetic flow field causes induced vortices around a fully conducting particle... 

Fig. 3 Sequences of a microvalve which is operated by induced-charge electrokinetics using a heterogeneous particle inside it. The flow pattern and vortices are shown by plotted streamlines. The normalized vectors show the direction of the fluid. The diameter of the heterogeneous particle and the microchamber are 20 and 40 pm, respectively. The height of the microchamber is 40 pm. The results are presented at the x-z plane crossing the middle of the 3D microvalve at different time steps. The zeta potential on the nonconducting hemisphere of the heterogeneous particle is set to —50 mV, while the zeta potentials on the nonconducting microchannel and microchamber walls are set to —15 mV...

Applications of Induced-Charge Electrokinetic in Microfluidics, Fig. 4 Flow pattem and concentration distribution in the micromixer. The red lines inside the microchamber represent the streamlines of the flow field. The color bar shows the concentration distribution. The figure shows a micromixing chamber (a) without a particle inside, (b and c) with a conducting particle at different... 

Nonlinear electrokinetic phenomena are electrically driven fluid flows or particle motions, which depend nonlinearly on the applied voltage. The term is also used more specifically to refer to induced-charge electroosmotic flow, driven by an electric field acting on diffuse charge induced near a polarizable surface. 

Once the electrochemical problem is solved, the ICEO flow is obtained by solving Stokes equations, Vp = r/V u and V-u = 0, with elec-troosmotic shp given by Eq. 1 with the induced zeta potential, C = Although this set of approximations can only be justified at low voltages in a dilute solution [9], it has had many successes in predicting induced-charge electrokinetic phenomena in experiments outside this regime. 

In addition to conventional pressure driven flow, electrokinetic flow is also a commonly used means of transporting liquids in microfluidic devices. One type of electrokinetic flow, electroosmotic flow, relies on the presence of an electrical double layer at the solid-liquid interface. A negatively charged surface in a flow channel will attract cationic species from the fluid to form an electrical double layer at the surface. Application of an external voltage can pull those cationic species through the flow channel inducing bulk flow. The electroosmotic flow velocity can be described... 

AC electroosmosis (ACEO) is a nonlinear electrokinetic phenomenon of induced-charge elec-troosmotic flow around electrodes applying an alternating voltage. 

Another puzzling feature of ACEO is the strong decay of the flow with increasing salt concentration. For this reason, all experiments in the literature have used either very dilute solutions (mostly KCl) or water (deionized or from the tap). A few groups have studied the concentration dependence of ACEO in aqueous KCl solutions [3, 15, 16]. These experiments and recent work on electrokinetic motion of heterogeneous particles suggest that flows due to induced-charge electroosmosis exhibit... 

The electrokinetic motion of polarizable particles results from electroosmotic flow (induced-charge electrophoresis) of the first of second kind, in addition to electrostatic forces ( dielectrophoresis). 

Electrokinetic Motion of Polarizable Particles, Fig.1 (a) Induced-charge electroosmotic ICEO) flow around a symmetric, uncharged, ideally polarizable particle [3] (b) an example of ICEO flow and the resulting induced-charge electrophoretic ICEP) velocity for an asymmetric shape [4]... 

The possibility of nonlinear electroosmotic flow, varying as m oc E, seems to have been first described by Murtsovkin [1, 2], who showed that an alternating electric field can drive steady quadrupolar flow around a polarizable particle (Fig. la). This effect has recently been unified with other nonlinear electrokinetic phenomena in microfluidics [3], such as AC electro-osmotic flow (ACEO) at microelectrodes [4, 7, 8] (Fig. lb), DC electrokinetic jets at dielectric corners [5] (Fig. Ic), and nonlinear flows around metal posts [9] (Fig. Id-e). These are all cases of induced-charge electroosmosis (ICEO) - the nonlinear electroosmotic flow resulting firom the action of an electric field on its own induced diffuse charge near a polarizable surface. 

Induced-charge and second-kind electrokinetic phenomena arise due to electrohydrodynamic effects in the electric double layer, but the term nonlinear electrokinetic phenomena is also sometimes used more broadly to include any fluid or particle motion, which depends nonlinearly on an applied electric field, fit the classical effect of dielectrophoresis mentioned above, electrostatic stresses on a polarized dielectric particle in a dielectric liquid cause dielectro-phoretic motion of particles and cells along the gradient of the field intensity (oc VE ). In electrothermal effects, an electric field induces bulk temperature gradients by Joule heating, which in turn cause gradients in the permittivity and conductivity that couple to the field to drive nonlinear flows, e.g., via Maxwell stresses oc E Ve. In cases of flexible solids and emulsions, there can also be nonlinear electromechanical effects coupling the... 

The theoretical description of nonlinear electrokinetic phenomena is challenging and not yet fully developed. In most of our exanples below, we focus on the motion of an ideally polarizable particle, which maintains uniform potential (0 and constant total charge Q without passing any direct current we also neglect surface conduction and specific adsorption of ions. Under these conditions, induced-charge electro-osmotic flows are strongest, and a general mathematical framework has been developed [2—5] for the weakly nonlinear limit of thin double layers where the bulk salt concentration (and conductivity (Tb) remains nearly constant. 

Electrokinetic Motion of Polarizable Particles, Figure 1 (a) Induced-charge electro-osmotic (ICEO) flow around a symmetric, uncharged, Ideally... 

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