Allan J. Easteal

Measurement of (p, V, x) for (water + acetonitrile) at 298.15 K

Abstract Volume ratios have been measured at (298.15 ± 0.02) K and pressures up to 250 MPa for {(1− x )H 2 O + x CH 3 CN}, using a bellows volumometer. From densities measured at 0.1 MPa together with the volume ratios at higher pressures, molar excess volumes, partial molar volumes, and isothermal compressibilities have been evaluated as a function of pressure and mixture composition. From the pressure variation of excess volume, the effect of pressure on excess Gibbs free energies has been calculated as a function of composition. The volume ratio has a maximum value at x ≈ 0.04, at pressures up to 250 MPa, suggesting that the initial effect of addition of CH 3 CN to H 2 O is to enhance the water network. The pressure variation of the partial molar volume of H 2 O has been interpreted as indicating a pressure-induced change in molecular packing for mixtures with x ≈ 0.8.

The temperature and density dependences of the self-diffusion coefficient and the shear viscosity of liquid trichloromethane

Self-diffusion coefficients for trichloromethane are reported for the temperature range 5–75°C at pressures up to 400 MPa, having been measured by both diaphragm cell and NMR spin-echo techniques. Shear viscosities, determined with a falling-body viscometer, are reported in the range 5–50°C and up to 300 MPa. The results are analysed with the aid of models derived from computer simulation molecular dynamics data.

(p, V, T) behaviour for formamide in the range 288 to 323 K and 0.1 to 280 MPa

Abstract The ( p , V , T ) behaviour of formamide has been determined with a bellows-type volumometer at 283.15, 298.15, 313.15, and 323.15 K and pressures up to 280 MPa. From the temperature and pressure dependence of the volume ratio, together with densities at 0.1 MPa, the isothermal compressibility, thermal expansivity, and internal pressure have been evaluated as functions of temperature and pressure. The results show that formamide is a relatively incompressible liquid which exhibits a considerable degree of water-like behaviour.

Tracer diffusion in hard-sphere liquids from molecular dynamics simulations

Abstract From molecular dynamics simulation results for diffusion in binary hard-sphere mixtures with solute (component 2) mole fractions 0.12, 0.2, 0.3 and 0.5, the limiting ( x 2 =0) tracer diffusion coefficient ratios D 2 0 / D E(12) , where D E(12) is the Enskog mutual diffusion coefficient, have been evaluated for solvent/solute mass ratios from 0.6 to 1.0, and solvent/solute diameter ratios from 1.0 to 2.0. Isotope effects for tracer diffusion, calculated from these data, are compared with experimentally determined isotope effects.

(p, Vm, T, x) measurements for [(1 − x)H2O + xCH3OH] in the range 278 to 323 K and 0.1 to 280 MPa II. Thermodynamic excess properties

Abstract Excess molar volumes are reported for [(1 − x )H 2 O + x CH 3 OH] from 0.1 MPa to 275 MPa at 278.15, 288.15, 298.15, 313.15, and 323.15 K. The values are used to calculate changes in the excess molar Gibbs energy, the excess molar enthalpy, and the excess molar entropy. Literature excess molar Gibbs energies and an excess molar enthalpy at 0.1 MPa are used to obtain the excess molar Gibbs energy and excess molar entropy under pressure. There is good agreement between the changes in excess molar enthalpy at 298.15 K and 50 MPa with literature values obtained directly. Systematic differences between the present excess molar volumes and limited literature values for x = 0.5 are attributed to difficulties in the experimental method used to obtain the latter. A comparison with [(1 − x )H 2 O + x CH 3 CN] at 298.15 K shows virtually no similarities in the dependence of the excess quantities on composition. It is unlikely that the (unbonded) accommodation of acetonitrile in the water structure thought to occur in (water + acetonitrile) has an analogue in (water + methanol).

Measurement of (p, V, x) for (ethanol+trichloromethane) at 298.15 K

Abstract Volume ratios have been measured at (298.15±0.02) K and pressures up to 250 MPa for {(1− x )CHCl 3 + x CH 3 CH 2 OH} using a bellows volumometer. From densities measured at 0.1 MPa together with the volume ratios at higher pressures, excess molar volumes, partial molar volumes, and isothermal compressibilities have been evaluated as functions of pressure and composition.

Diffusion in mixtures of hard spheres at liquid densities: A comparison of molecular dynamics and experimental data in equimolar systems

Abstract Computer simulations by molecular dynamics have been used to obtain the diffusion coefficient of both components in an equimolar mixture of 250 smooth hard spheres. The data cover a closely spaced V/V 0 range from 1.5 to 4 with mass ratios in the range 1–10 and diameter ratios in the range 1–3. They are used to examine the effects on the diffusion coefficients of differing mass and size, of isotope effects and also are compared with experimental data for eleven real systems. It is concluded that the simulation data enable prediction of diffusion coefficients for systems in which the effects of molecular interactions are not strong.

Chemical effects in diffusion and structure of zinc chloride in aqueous solution

Abstract In the absence of neutron data, we have examined existing experimental data for X-ray, Raman scattering, EXAFS and thermodynamic activity studies in order to build up a consistent model of the structure of ZnCl 2 in aqueous solution in the range of molality from 2 up to saturation. The structure that emerges is that Zn is tetrahedrally coordinated and that in these coordination complexes the number of Cl ions per Zn ion increases with increasing molality, this implying the existence of extended Zn structures as the saturation concentration is approached. Relevant evidence in support of these structural models has been obtained by measuring the diffusion constants of Zn. Cl and H 2 O when the stoichiometry of the solution is varied by replacing Zn by Li. This evidence strongly supports the model in which available Cl ions form complexes with Zn up to at least four Cl ions per Zn ion.

Experimental measurements, molecular dynamics simulations and application of a rough-hard-spheres model for tracer diffusion in Octamethylcyclotetrasiloxane at 323 K and pressures up to 59 MPa

Abstract Tracer diffusion measurements have been made for seven solutes at pressures up to 59 MPa in octamethylcyclotetrasiloxane (OMCTS) at 323 K. Molecular dynamics simulations in hard-sphere mixtures corresponding in molecular size and mass ratios to those of the constituents of the solutions are reported and used to analyse the experimental data by employing a rough-hard-spheres model. The results show a close similarity in diffusional behaviour in OMCTS of carbon tetrachloride and OMCTS. In general, it is the relative size of solute to solvent that determines the rate of diffusion although there appear to be specific interaction effects for methanol, ethanol and acetonitrile.

Diffusion of water in solutions of alkali metal bromides, tetraalkylammonium bromides and ammonium bromide

The diffusion coefficient of water Dw in aqueous solutions of the alkali metal bromides, tetraalkylammonium bromides (methyl, ethyl, n-propyl, and n-butyl) and ammonium bromide at 25°C is reported for concentrations up to 2 mol-dm−3. In addition, values for Dw in 2 mol-dm−3 solutions of CsBr, KBr, NaBr, LiBr, and fully deuterated methanol, acetonitrile, and acetone have been measured for temperatures in the range 5 to 50°C. The concentration dependence of the relative water diffusion coefficient Dw/Do, where Do is the self-diffusion coefficient of water, has been analyzed in terms of an equation analogous to the Jones-Dole equation for relative viscosity. The B-coefficient for diffusion is well correlated with the viscosity B-coefficient. For the structure-breaking electrolytes CsBr and KBr, Dw/Do decreases rapidly with increasing temperature, whereas for the structure-makers NaBr and LiBr, the temperature dependence of Dw/Do has the same sign but is much smaller in magnitude. For the nonelectrolyte solutions, the structure-making effect decreases with increasing temperature and the temperature coefficient of Dw/Do is positive. It is apparent that, when diffusion of the solvent is being considered, the temperature must be taken into account in the classification of an electrolyte as a structure-breaker or structure-maker.