Effect of concentration on the thermodynamics of sodium chloride aqueous solutions in the supercooled regime

Molecular dynamics simulations are performed on two sodium chloride solutions in TIP4P water with concentrations c=1.36 mol/kg and c=2.10 mol/kg upon supercooling. The isotherms and isochores planes are calculated. The temperature of maximum density line and the limit of mechanical stability line are obtained from the analysis of the thermodynamic planes. The comparison of the results shows that for densities well above the limit of mechanical stability, the isotherms and isochores of the sodium chloride aqueous solution shift to lower pressures upon increasing concentration while the limit of mechanical stability is very similar to that of bulk water for both concentrations. We also find that the temperature of maximum density line shifts to lower pressures and temperatures upon increasing concentration. Indications of the presence of a liquid-liquid coexistence are found for both concentrations.