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

Dipartimento di Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Roma, Italy.
The Journal of Chemical Physics (Impact Factor: 2.95). 05/2009; 130(15):154511. DOI: 10.1063/1.3119634
Source: PubMed


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.

1 Follower
20 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we investigate the possibility to detect the hypothesized liquid-liquid critical point of water in supercooled aqueous solutions of salts. Molecular dynamics computer simulations are conducted on bulk TIP4P water and on an aqueous solution of sodium chloride in TIP4P water, with concentration c=0.67 mol/kg. The liquid-liquid critical point is found both in the bulk and in the solution. Its position in the thermodynamic plane shifts to higher temperature and lower pressure for the solution. Comparison with available experimental data allowed us to produce the phase diagrams of both bulk water and the aqueous solution as measurable in experiments. Given the position of the liquid-liquid critical point in the solution as obtained from our simulations, the experimental determination of the hypothesized liquid-liquid critical point of water in aqueous solutions of salts appears possible.
    The Journal of Chemical Physics 04/2010; 132(13):134508. DOI:10.1063/1.3376776 · 2.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Jagla ramp particles, interacting through a ramp potential with two characteristic length scales, are known to show in their bulk phase thermodynamic and dynamic anomalies, similar to what is found in water. Jagla particles also exhibit a line of phase transitions separating a low density liquid phase and a high density liquid phase, terminating in a liquid-liquid critical point in a region of the phase diagram that can be studied by simulations. Employing molecular dynamics computer simulations, we study the thermodynamics and the dynamics of solutions of hard spheres (HS) in a solvent formed by Jagla ramp particles. We consider the cases of HS mole fraction xHS=0.10, 0.15, and 0.20, and also the case xHS=0.50 (a 1:1 mixture of HS and Jagla particles). We find a liquid-liquid critical point, up to the highest HS mole fraction; its position shifts to higher pressures and lower temperatures upon increasing xHS. We also find that the diffusion coefficient anomalies appear to be preserved for all the mole fractions studied.
    Physical Review E 06/2010; 81(6 Pt 1):061504. DOI:10.1103/PhysRevE.81.061504 · 2.29 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper we compare recent results obtained by means of molecular dynamics computer simulations on the thermodynamics of TIP4P bulk water and on solutions of sodium chloride in TIP4P water. The concentrations studied are c = 0.67, 1.36 and 2.10 mol kg( - 1). The results are checked against change of water-salt potential and size effects. The systems are studied in a wide range of temperatures, going from ambient temperature to the supercooled region. Analysis of simulated state points, performed on the isochores and on the isotherm plane, allowed the determination of the limit of mechanical stability and of the temperature of maximum density lines. While the presence of ions in the system does not affect the limit of mechanical stability with respect to the bulk, it causes the temperature of the maximum density line to shift to lower pressure and temperature upon increasing concentration. The occurrence of minima in the trend of potential energy as a function of density and the inflections in the low temperature isotherms suggest the presence of liquid-liquid coexistence for bulk water and for the sodium chloride solutions at all concentrations studied.
    Journal of Physics Condensed Matter 07/2010; 22(28):284104. DOI:10.1088/0953-8984/22/28/284104 · 2.35 Impact Factor
Show more


20 Reads
Available from