Numerical study of ionic current rectification through non-uniformly charged micro/nanochannel systems

Ionic transport through cylindrical nanochannels with linearly varied surface charge density was numerically investigated. The ends of the nanochannel were connected to microchannels regarded as reservoirs. The walls at the micro/nanochannel junction were referred to as sidewalls that can be electrically neutral or charged. The results showed that the charged sidewalls could enhance the concentration polarization compared to neutral sidewalls. For neutral sidewall, a limiting current similar to charged permselective membranes and a maximum current rectification ratio at certain bulk concentration similar to charged conical nanopores can be found. For the charged sidewall case, no limiting current regime can be observed and the current varied linearly with the applied voltage with a larger slope compared to the Ohmic relation regime. Moreover, no maximum current rectification ratio can be found and the current rectification ratio increased with the decrease in bulk concentration and increases in surface charge density and sidewall length.