Charge Inversion and Flow Reversal in a Nanochannel Electro-osmotic Flow

Ion distribution and velocity profiles for electro-osmotic flow in a 3.49 nm wide slit channel with a surface charge density of -0.285 C/m(2) are studied using molecular dynamics simulations. Simulation results indicate that the concentration of the co-ion exceeds that of the counterion in the region 0.53 nm away from the channel wall, and the electro-osmotic flow is in the opposite direction to that predicted by the classical continuum theory. The charge inversion is mainly caused by the molecular nature of water and ions. The flow reversal is caused by the immobilization of counterions adsorbed on the channel wall and due to the charge inversion phenomena.