Atomistic simulation study of charge inversion in silica nanochannels

Recent experiments report charge inversion, i.e. interfacial charges attracting couterions in excess of their own nominal charge, in divalent ionic solutions near charged silicon oxide interfaces. We have conducted a series of atomistic molecular dynamics simulations in order to investigate the mechanism of charge inversion in these systems. We studied both CaCl$_2$ and MgCl$_2$ solutions near an amorphous silica substrate which had a charge density of $\sim 1/50${\AA}$^2$. Our simulation results give a detailed description of the structure of the ions and water near the silica interface. Finally, we show that our simulations are in remarkable agreement with the experimental results.