Atomistic simulation of KCl transport in charged silicon nanochannels: Interfacial effects

Electroosmotic flow is an important fluid transport mechanism in nanofluidic systems. In this paper, we investigate the ion distribution and velocity profiles of KCl solution in two oppositely charged silicon nanochannels by using molecular dynamics simulations. The continuum theories, based on the Poisson-Boltzmann equation and the Navier-Stokes equations, predict that the distribution of the counter-ions, water flux and ionic conductivity in the two oppositely charged channels are the same. However, molecular dynamics simulations show very different results. First, the counter-ion distributions are substantially different in the two channels. Second, the water flux and ionic conductivity in the two channels differ by a factor of more than three. Third, the co-ion fluxes are in the opposite direction. The different counter-ion distributions in the two channels are attributed to the different size of the K+ and Cl− ions and the discreteness of the water molecules, and the asymmetric dependence of the water and ion transport is attributed to the asymmetric dependence of the hydrogen bonding of water near the charged silicon surface, which influences the dynamic behavior of interfacial water significantly.