Enhancement of mass transport and separation of species by oscillatory electroosmotic flows

Mass transport driven by oscillatory electroosmotic flows (EOF) in a two-dimensional micro-channel is studied theoretically. The results indicate that the velocity and concentration distributions across the channel-width become more and more non-uniform as the Womersley number W, or the oscillation frequency, increases. It is also revealed that, with a constant tidal displacement, the total mass transport rate increases with the Womersley number W due to both the stronger convective and the transverse dispersion effects. The total mass transport rate also increases with the tidal displacement (with a fixed oscillation frequency) because of the associated stronger convective effects. The cross-over phenomenon of the mass transport rates for different species becomes possible with sufficiently large Debye lengths and at sufficiently large values of W. Consequently, with proper choices of the Debye length, oscillation frequency and tidal displacement, oscillatory EOF may become a good candidate for the first-step separation of the mass species.