Volume 227, Issue 2-3 - Special Issue Prof. Heintz

The influence of sodium sulphate on the solubility of carbon dioxide in aqueous solutions of N,N-dimethylmethanamide {= N,N-dimethylformamide, (CH 3 ) 2 N-C(H)O, DMF} was investigated experimentally at three temperatures (314 K, 354 K, and 395 K). The solvent was an aqueous solution of DMF (mole fraction of DMF in the salt-free solution ≈ 0.05) and sodium sulphate (molality ≈ 0.6 mol·(kgH 2 O) −1 ). The maximum pressure of the new experimental gas solubility data reaches nearly 10 MPa. A thermodynamic model that combines two models for the solubility of CO 2 (in aqueous solutions of Na 2 SO 4 on one side and in aqueous solutions of DMF on the other side) is used to predict the influence of Na 2 SO 4 on the solubility of CO 2 in aqueous solutions of DMF. The new experimental data are compared with such predictions and with calculations from an extension of that model where a single ternary parameter for interactions between the three solutes ( i.e. , CO 2 , Na 2 SO 4 , and DMF) is adjusted to improve the representation of the experimental data.

The interfacial tension between demixed liquids has a large impact on the mass transfer over the phase boundary. In this paper a special version of the density-gradient theory for ternary systems, where the grand thermodynamic potential is calculated using the Koningsveld–Kleintjens model, is suggested. This approach allows the prediction of the interfacial tensions of practical important ternary systems based on information of the binary subsystems. In order to verify this idea two ternary systems showing only one miscibility gap, namely water + butan-1-ol + ethanol and water + acetone + toluene, were selected. The predicted interfacial tensions were very close to the experimental data taken from the literature and to own experimental data obtained by spinning drop measurements. Both systems differ in the enrichment behavior. Whereas ethanol will be enriched in the interface to a small amount, the enrichment of acetone is much more pronounced.

Theoretical calculations of the conductivity of sodium chloride in water + 1,4-dioxane mixtures are presented and compared with experimental measurements. The method of direct correlation force in the framework of the interionic theory is used for the calculation of transport properties in connection with the associative mean spherical approximation (AMSA). The effective interactions between ions in solutions are derived with the help of Monte Carlo calculations on the Born–Oppenheimer level. This work is based on earlier studies on structure of dioxane + water mixtures and the solvation of ions in it.

A previously developed ab initio virial equation of state for argon (B. Jäger, R. Hellmann, E. Bich, E. Vogel, J. Chem. Phys. 135 (2011) 084308) was applied to calculate related thermophysical properties for the gaseous and supercritical region. Virial coefficients up to B 7 were included considering also nonadditive three-body interactions and quantum corrections (for B 2 , B 3 , and B 4 ). The results for the isothermal compressibility, the thermal expansivity, the isochoric and isobaric heat capacity, and for the speed of sound were compared with experimental data and with values obtained from a highly accurate empirical equation of state. It was generally found that the theoretical predictions are in very good agreement with the reference data except for the near-critical region and for higher densities. Hence, the theoretically calculated data can be useful for the improvement of equations of state, particularly for toxic or corrosive substances and for thermodynamic conditions, where experiments are difficult to perform ( e.g. at high temperatures). The speed of sound was found to be the most suitable property to evaluate the quality of the underlying interaction potentials.

Results of new relative measurements on the vapor of acetic acid are reported. The measurements were based on a single calibration at room temperature with a theoretically calculated viscosity value of argon. Nineteen isochoric series, differing in density, were performed in an all-quartz oscillating-disk viscometer from 298 to 598 K and for densities between 0.5 and 61 mol m -3 . The uncertainty of the experimental data is ±0.5% at low densities and ±(0.3−0.4)% at high densities increasing with temperature. This is inferior compared with measurements on simple gases due to adsorption effects on quartz at low temperatures and to thermal decomposition at high temperatures. Isotherms recalculated from the original isochoric data show with decreasing density a strong curvature with negative slope, particularly at low temperatures. The further evaluation accounts for the fact that a strong dimerization depending on temperature occurs in acetic acid vapor. The isotherms, resulting from an association model which considers additional interactions between monomers and dimers, show a smaller curvature in terms of the mole fraction of monomers. Viscosity values for monomers and dimers were deduced using a simplified equation for the viscosity of a gas mixture. These values are restricted to 570 K due to thermal decomposition and low mole fractions of the dimers at high temperature. Furthermore, viscosity values for the saturated vapor could be determined at low temperatures.

The second osmotic virial coefficient and the apparent molar mass of two human and one mouse monoclonal antibodies were measured in different aequeous buffer solutions which also contained sodium chloride or ammonium sulfate, respectively, by static laser light scattering in batch mode. The apparent molar mass indicates aggregation. At a constant pH value of 6.5 the sodium chloride concentration was varied from 0 to 2 M and the ammonium sulfate concentration from 0 to 0.8 M, respectively. A 20 mM sodium-phosphate buffer was used for all experiments. Furthermore the pH value was varied without adding additional salt from 4.5 to 10. The results of the salt dependency are in line with the Hofmeister-series. The results of the pH dependency correspond to the net charge of the molecules.

The computation of distances between interactions sites while observing the minimum image convention is one of the most frequently performed operations in computer simulations of fluids. In this work several ways of encoding the minimum image convention are discussed and their performances on different computers compared. It turns out that the optimal choice for the algorithm depends on the computer type as well as the optimization level of the compiler, and that a well adapted algorithm can achieve a significant reduction of the computation time.