Computational studies of aqueous interfaces of SrCl(2) salt solutions

The electron density profiles and corresponding surface structures of an aqueous interface of SrCl(2) salt solution were computed by use of molecular dynamics simulations. We used both polarizable and nonpolarizable potential models to describe molecular interactions. The results demonstrate that the polarizable models captured the essential features of the corresponding X-ray reflectivity experimental data while the corresponding nonpolarizable models could not. In addition, we demonstrated that the shape of the X-ray reflectivity curve could be quantitatively reproduced if the simulations were carried out at lower SrCl(2) concentrations, making it likely that the polarizable models used in this study somewhat overestimate the surface concentration of ions. However, significant interfacial enhancement of both Sr(2+) and Cl(-) appears necessary to reproduce the experimental spectra. This is in contrast to systems with monovalent cations, which have generally been found to have a double layer, in which anions are enhanced at the surface but cations are repelled.