Molecular Dynamics Simulation of the Effects of NaCl on Electrostatic Properties of Newton Black Films

Abstract

The effects of NaCl on electrostatic properties of Newton black films (NBF) coated with two monolayers of sodium dodecyl sulfate were investigated by using molecular dynamics simulations. Film systems without salt and with 1.0 mol/L NaCl were studied separately. Charge density profiles of salt ions are calculated and fitted using a function we proposed. Fitting results show that adding NaCl leads to more positive charge adsorbed to the surface and less diffusing in the middle of the film. More positive charge adsorbed to the surface leads to the destruction of solvation shells around amphiphilic groups, so that water molecules arrange less regularly. Adding NaCl leads to a decrease of both ions and water contributions to the electrostatic field, which are controlled by ionic charge distributions and water orientations. The relative decrements of ions and water contributions determine the difference in electrostatic potential. On the basis of the investigation of electrostatic potential and species distrib...