Numerical prediction of ac electro-osmotic flows around polarized electrodes

In this paper we present an interactive numerical method that can predict ac electro-osmotic flows around completely polarized electrodes. In this method the slip velocity on the electrode surface is calculated by numerically solving the Laplace equation for the potential in the bulk coupled with the dynamical equation for the surface charge density on the electrodes; here the dynamical equation has been derived from the asymptotic solutions of the Poisson-Nernst-Planck equation for the potential drop across the electrical thin layer near the electrode. A unique feature of this study is that the effect of nonspecific ion adsorption is considered. The numerical code was applied to the two-dimensional ac electro-osmotic flow above a pair of coplanar electrodes, and the solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness, and the adsorption coefficients.