Ion-size effect on electrokinetic energy conversion in nanofluidic channels

The present study utilizes a modified Poisson–Boltzmann (MPB) equation to take into account ion-size (steric) effect and then performs a series of simulations to investigate the ionic transport phenomenon within two nanofluidic devices, namely a nanoslit and a nanotube. The results show that at all electrolyte concentrations, the streaming conductance increases when the ion-size effect is taken into account, particularly under conditions of high surface charge density. The net charge density is amplified by the ion-size effect for both nanogeometries as well. The enhancement in the streaming conductance is particularly pronounced in the nanotube since the net charge density has higher value by the geometry effect of the nanotube. The maximum ratio of net charge density (ρ_{e steric}/ρ_{e non-steric}) is 1.55 near the surface of nanotube. In addition, it is shown that for both configurations, the contribution of electroosmotic flow to the electrical conductance increases when the finite ion size is taken into account.