Electrokinetic transport in silica nanochannels with asymmetric surface charge

Abstract

The characteristic high surface area to volume ratio causes ionic transport in nanofluidic devices to be governed by surface properties like surface charge. In recent years, experimental demonstrations have shown gate electrodes embedded in the nanochannel wall to systematically alter the surface potential to manipulate ionic transport in nanochannels. Using state-of-the-art non-equilibrium molecular dynamics simulations, electrokinetic transport of an aqueous KCl solution confined in a ~7 nm deep silica nanochannel is reported under the influence of asymmetric surface charge to investigate the effect of engineered surface charge on the resulting velocity and ion number density profiles within these nanochannels. Significant changes in the velocity magnitude and profile were observed in the silica nanochannels with two charged surface patches compared to a homogenously charged silica channel. The surface charged patches cause regions of local flow reversal which were indicated by an observed negative velocity. The simulations provide a theoretical foundation to systematically manipulate electrokinetic flow inside nanochannels by using engineered surface charge at the nanochannel walls.