Electroosmotic flow through an annulus

The electro-osmosis through an annulus is investigated. The electric potent ial and flow velocity profile are obtained by solving the linearized Poisso n-Boltzmann equation and the Stokes equation. Both the thin and thick doubl e layer limits are analyzed. Under the condition of thin double layer, the electro-osmotic mobility can be described by the Helmholtz-Smoluchowski equ ation with a geometry-dependent correction factor. There exist net flows ev en for zero area-averaged surface charge density due to the curvature diffe rences between the inner and outer walls. The flow direction is determined by the sign of the charge on the inner cylinder. We also found that under c ertain circumstances the flow direction in an annulus is opposite to that i n a capillary with the same sign of the net charge. (C) 2000 Academic Press .