Molecular simulation of aqueous electrolytes in model silica nanochannels

Aqueous electrolytes, NaCl and CaCl2, were simulated via molecular dynamics in nanochannels with radius ranging from 0.5 to 1.5 nm using a united-atom Lennard-Jones model for the SiO2 surface and the SPC/E water model. The effects were studied of nanochannel radius and charges on the wall upon the radial density profiles and axial self-diffusivities of water and ions. Only small effects of the wall were found on the axial movement of water molecules and ions. Discrete charges on the wall exert little influence on the distribution of water molecules and ions except for the strong adsorption of sodium ions at the charge sites. Surface charges were neutralized by the adsorbed sodium ions, which were essentially immobilized at the surface charge sites.