Effect of Intrachannel Ion Transport on Transient Characteristics of Nanochannels

This study numerically and theoretically investigates the transient responses of nanofluidic channels under step-like voltage biases. Time-dependent simulations based on Poisson-Nernst-Planck equations demonstrate that in the Ohmic regime of electrical conductance, the transient characteristics are distinctively different from those in the limiting regime. Whereas the latter has been previously shown to be due to the dynamics of ion depletion in the reservoirs, the present study shows that the former is mainly due to the propagation of ion accumulation inside the channels. Our further analysis derives expressions for the characteristic transient times in the Ohmic regime based on the ambipolar nature of the ion transport. The derived expressions are correlated with numerical simulations for examining the dependence of the characteristic transient times on important device parameters as well as the effect of electro-osmotic flow.