Investigation of charge inversion in silicon nanochannels with molecular dynamics simulation

Abstract

Through molecular dynamics simulation, the ionic distributions in NaCl and CaCl₂ solutions confined in 3-nm-high nanochannels were investigated. Different from the previous simulation model with artificial electrical neutrality, our model would reach equilibrium and electrical neutrality through ion exchange among the nanochannel region and the bulk sinks. It is observed that when the surface charge density is −0.101 C/m², charge inversion occurs at 1.0 M concentration of CaCl₂ solution, but not in NaCl solution due to the stronger correlation effect between Ca²⁺ ions near the charged surface, which is not considered in the mean field Poisson–Boltzmann equation. Our simulation results agree well with the experimental results by F.H.J. Van Der Heyden et al. In addition, with the increase in the surface charge density, the charge inversion can be induced in the monovalent solution and be strengthened in the divalent ionic solution.