Elimination of pseudo-negative conductance by coercive steady state in perm-selective ion transportation.

Ion concentration polarization (ICP) has drawn unprecedented attention due to its new underlying physics and engineering applications such as biomolecular preconcentrator and electrofluidic desalination. Typically, the current-voltage characteristic of ICP has three distinctive regimes with a positive slope in all regimes, but an unintentional negative slope ("overshoot current") was often observed in the Ohmic/limiting regime. This phenomenon impeded an exact estimation of electrokinetic properties of the ICP platform. Therefore, in this work, we eliminated overshoot current by limiting the length of the diffuse layer using a coercive injection of a fresh electrolyte solution. Both the visualization of ICP layer propagation and the measurement of current-voltage characteristics verifying the time for reaching the steady state within an effective length of a microchannel played a critical role. The most relevant parameter was shown to be the diffusion relaxation time which was directly correlated with the sweep rate of an external voltage. Using this new measurement platform, one can significantly reduce the time and labor for the electrokinetic studies and applications based on them.