1,721,036 research outputs found
Structural Properties of High and Low Density Water in a Supercooled Aqueous Solution of Salt
No full text"We consider and compare the structural properties of bulk TIP4P water and of a sodium chloride aqueous solution in TIP4P water with concentration c = 0.67 mol\/kg, in the metastable supercooled region. In a previous paper (Corradini, D.; Rovere, M.; Gallo, P. J. Chem, Phys. 2010, 132, 134508) we found in both systems the presence of a liquid liquid critical point (LLCP). The LLCP is believed to be the end point of the coexistence line between a high density liquid (HDL) and a low density liquid (LDL) phase of water. In the present paper we study the different features of water water structure in HDL and LDL both in bulk water and in the solution, We find that the ions are able to modify the bulk LDL structure, rendering water water structure more similar to the bulk HDL case. By the study of the hydration structure in HDL and LDL, a possible mechanism for the modification of the bulk LDL structure in the solution is identified in the substitution of the oxygen by the chloride ion in oxygen coordination shells.
A route to explain water anomalies from results on an aqueous solution of salt
No full textIn 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
Structure and thermodynamics of supercooled aqueous solutions: Ionic solutes compared with water in a hydrophobic environment
No full text"Molecular dynamics results are presented for bulk TIP4P water and for aqueous solutions of sodium chloride at two different concentrations. Thermodynamical and structural properties are calculated in the supercooled region. The behaviour in the thermodynamic plane is compared with the case of water in interaction with a hydrophobic environment. Structural modifications induced by the hydrophilic and hydrophobic interactions are discussed. It is found that the phase diagram of water is shifted in different directions in the case of the hydrophobic system and the ionic solutions. The region inside the temperatures of the maximum density curve is reduced upon increasing the concentration of ions. (C) 2010 Elsevier B.V. All rights reserved.
Effect of concentration on the thermodynamics of sodium chloride aqueous solutions in the supercooled regime
No full textMolecular 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
Widom line and dynamical crossovers: routes to understand supercritical water
No full textSupercritical water is fundamental in many fields of applications and a precise characterization
of the supercritical state is of uttermost importance for this liquid. In a fluid,
when moving from the critical point into the single-phase region, the thermodynamic
response functions show maxima reminiscent of the critical divergence. Here we study the
thermodynamic properties of water in the supercritical region by analysing both available
experimental data and our computer simulation results. We find that the lines connecting
the maxima of the response functions converge on approaching the critical point in a single
line, the Widom line. We further show that the Widom line coincides with a crossover from a
liquid-like to a gas-like behaviour clearly visible in the transport properties. These thermodynamic
and dynamic features show that the supercritical state in water is far more complex
than what was so far believed, indicating a new perspective in the characterization of the
thermodynamics of this state
Liquid-Liquid Coexistence in NaCl Aqueous Solutions: A Simulation Study of Concentration Effects
No full textIn this paper we investigate by means of molecular dynamics computer simulations how the hypothesized liquid-liquid critical point of water shifts in supercooled aqueous solutions of salt as a function of concentration. We study sodium chloride solutions in TIP4P water, NaCl(aq), for concentrations c = 1.36 mol/kg and c = 2.10 mol/kg. The liquid-liquid critical point is found up to the highest concentration investigated, and its position in the P-T plane shifts to higher temperatures and lower pressures upon increasing concentration. For c = 2.10 mol/kg it is also located very close to the temperature of maximum density line of the system. The results are discussed and compared with previous results for bulk TIP4P water and for c = 0.67 mol/kg NaCl(aq) and with experimental findings. We observe a progressive shrinkage of the low-density liquid region when the concentration of salt increases; this suggests an eventual disappearance of the liquid-liquid coexistence upon further increase of NaCl concentration
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