High Temperature Stability of Hydrated Ion Pairs Na+Cl–(H2O) N under Conditions of a Flat Nanopore

Abstract

The high-temperature stability of hydrated ion pairs under conditions of a nanoscopic flat pore with hydrophobic structureless walls is studied by computer simulations. The limited space of the nanopore stimulates dissociation of the contact ion pair (CIP) with its transition to the state of the solvent-separated ion pair (SSIP); moreover, the ion pair demonstrates a high degree of stability on heating. The inverse temperature effect where the heating renders a moderate consolidating effect on the state of a hydrated contact ion pair is observed: when heated to the electrolyte boiling point, the free energy barrier that separates the CIP and SSIP states shifts by 2 molecules towards the larger hydration shells. On the pressure scale, the boundary between CIP and SSIP states shifts at the same rate as the saturating pressure with the increase in the temperature.