Solute dispersion in oscillating electro-osmotic flow with boundary mass exchange

Mass transfer in an oscillatory electro-osmotic flow (EOF) is theoretically studied, for the case of a cylindrical tube with a reactive wall. An expression for the dispersion coefficient, reflecting the time-averaged mass flux of an electrically neutral solute, is derived analytically. Under the influence of a reversible solute-wall mass exchange, the dispersion coefficient exhibits a complex dependence on the various parameters representing the effects of the electric double-layer thickness, oscillation frequency, solution transport properties, solute partitioning, and reaction kinetics. Our results suggest that, in the presence of a reversible mass exchange at the wall, an oscillatory EOF may be used for separation of species. It is found that optimal conditions for separation are achieved for a thin double-layer, where an inert solute, or one with slow exchange kinetics, experiences virtually no dispersion while the dispersion is maximized for the reactive solute exhibiting fast kinetics.