Electroosmotic flow in slit microchannel containing salt-free solution

A theoretical study on the electroosmotic flow through a uniformly charged planar slit microchannel containing a salt-free solution is presented. Based on the exact analytical solutions for the electric potential distribution and the transient electroosmotic flow velocity, a systematic parametric study on the characteristics of the transient electroosmotic flow is then investigated. The results show that the general behavior of electroosmotic flow in a planar slit is similar to that in a cylindrical capillary; however, the characteristic time to reach the steady-state flow, the electroosmotic mobility and the correction factor to the Smoluchowski equation in a slit are larger than those in a cylinder with its diameter equal to the slit width. Furthermore, the osmotic pressure of counterion between two equally charged planar surfaces immersed in a salt-free solution is found to be always repulsive. In addition, the implications of these results on electroosmosis in a microchannel are discussed.