Time periodic electro-osmotic transport in a charged micro/nano-channel

The electro-osmotic flow in a micro- or nano-channel driven by an AC electric field is studied. The channel height is considered to be comparable to its width. We consider a mixture of water or another neutral solvent and a salt compound such as sodium chloride for which the ionic species are entirely dissociated. The distribution of ions is governed by the mass transfer equation, thus the Debye-Huckel approximation is not invoked. The time periodic EOF has been investigated for channel height varying from 5 to 50 nm. The sinusoidal electric field induces an oscillatory flow and the concentration of ionic species exhibits steady oscillation. The results indicate that there exists a phase lag between the applied electric field and the periodic EOF. This phase lag in axial flow varies with the channel height. Unlike the DC-ECF, here the core of the channel is not electrically neutral and hence a plug-like velocity profile is absent. (c) 2008 Elsevier B.V. All rights reserved.