Investigation of the Structure of Concentrated NaOH Aqueous Solutions by Combining Molecular Dynamics and Wide-Angle X-ray Scattering

Classical molecular dynamics has been performed with explicit polarization on NaOH aqueous solutions from 0.5 mol L^-1 up to 9.7 mol L^-1. We adapted a force field of OH^- for polarizable simulation in order to reproduce the NaOH structural and thermodynamics properties in aqueous solutions. A good agreement between theoretical and experimental results has been found. Wide-angle X-ray scattering (WAXS) intensities issued from molecular dynamics are compared to experimental ones measured on Synchrotron facilities. The structure of the first coordination shell of Na⁺ has been studied to determine the variation of the oxygen number and hydroxide oxygen around the cation. In addition, Na⁺-OH^- McMillan-Mayer potential issued from molecular dynamics simulations has been calculated and allows for calculating Na⁺-OH^- pair association constant of 0.1 L mol^-1, which is in good agreement with the experiments.