Theoretical Model of Electrode Polarization and AC Electroosmotic Fluid Flow in Planar Electrode Arrays

Comment on “Theoretical Model of Electrode Polarization and AC Electroosmotic Fluid Flow in Planar Electrode Arrays”

“…This letter is in response to a letter to the editor recently published in this journal (1), in which Kaler and co-workers made several incorrect assertions about our recent work on AC electroosmotic fluid flow on microelectrodes (2)(3)(4). The authors derived a model for the electroosmotic velocity that directly contradicts fundamental electrokinetic principles.…”

“…Substituting for the zeta potential (Eq. [1]) into Eq. [2] gives the velocity in terms of the surface charge density:…”

“…Scott et al (1) stated that in our RC model (2) we ignored the diffuse character of the double layer. In fact, our model was based upon the standard Debye-Hückel treatment on the diffuse double layer (5)(6)(7)(8).…”

“…According to Eq. [1], the diffuse double layer can be modeled as a capacitor with specific capacitance (capacitance per unit area) C s = εκ. This widely accepted framework for the double layer was used by us to develop a resistor-capacitor circuit model (2), which predicted the approximate frequency dependence and velocity of fluid flow.…”

Induced-Charge Electro-Osmosis

“…The same time scale, τ c , also arises as the inverse frequency of AC electro-osmosis (Ramos et al (1999)) or AC pumping (Ajdari (2000)) at a micro-electrode array of characteristic length a, where again an RC-circuit analogy has been invoked to explain the charging process. This simple physical picture has been criticized by Scott et al (2001), but Ramos et al (2001) and Gonzalez et al (2000) have convincingly defended its validity, as in the earlier Russian papers on polarizable colloids.…”