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–Hückel 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-EOF, here the core of the channel is not electrically neutral and hence a plug-like velocity profile is absent.