Double layer overlap in ac electroosmosis

The frequency-dependent flow of electrolytes between pairs of parallel plate micro-electrodes is analyzed in this paper, for the cases in which electric double layers formed in vicinity of the solid boundaries may strongly interact with each other. Closed form expressions for the potential distributions are first developed under certain simplifying assumptions, depicting the interactions between the oscillating electric field and charge density distribution within the double layer. It is revealed that the impact of double layer overlap on ac electroosmotic flows turns out to be more predominant at frequencies of the order of relaxation frequency of the electrode-electrolyte system. At higher frequencies, potential drop across the double layer tends to zero, due to polarization of the electrode-solution interface, and virtually no electroosmotic flows can be obtained in such cases. (c) 2007 Elsevier Masson SAS. All rights reserved.