We obtain the activity coefficients and lower bounds to the solubility of CaCl2 in aqueous solutions at temperatures between 298.15 and 473.15 K using molecular simulations with three previously developed nonpolarizable force fields. We find that a scaled-charge force field gives incorrect activity coefficients at low concentration and has a different absolute chemical potential than experiments, but still predicts an accurate solubility for the calcium chloride dihydrate. The two full-charge models have chemical potentials and activity coefficients closer to experiments, but there is considerable variation between them, with the chemical potentials differing by over 100 kJ·mol−1. The slow dynamics of the full-charge models at high concentrations are unrealistic and require advanced sampling methods to obtain the activity coefficients. We find that development of polarizable models is likely necessary to accurately represent both thermodynamic and transport properties of divalent electrolyte solutions.

No abstract

Phase equilibria of fluid substances and their mixtures are important in numerous scientific as well as industrial applications and are, therefore, a major focus of thermophysical property research. For the development and improvement of thermophysical property models, reliable experimental data are crucial. However, measurements of thermophysical properties in the vicinity of the dew line can be substantially distorted by surface phenomena such as adsorption and capillary condensation on the quasi nonporous metal surfaces of the experimental apparatuses. To support the qualitative understanding of these phenomena on an atomistic level and to estimate their impact on experiments, we performed classical molecular dynamics (MD) simulations. As a first proof-of-concept investigation, we focused on pure CO2 on an idealized face-centered cubic (fcc) {111} gold surface. The results, in the form of an adsorption isotherm at T = 283.15 K, are compared to sorption measurements using a specially designed gold sinker incorporated in an optimized gravimetric sorption analyzer. This first comparison between atomistic MD simulations and gravimetric experiments helps in assessing the applicability of our simulation technique and paves the way for a deeper understanding of the relevant surface phenomena occurring in our apparatus.

No abstract