Lawrence A. Woolf

Pressure and temperature dependence of the self diffusion coefficient of water and oxygen-18 water

The self diffusion coefficients of water, DS(H216O), and of oxygen-18 water, DS(H218O), have been measured over the temperature range 277–333 K and to pressures of 300 MPa by the n.m.r. spin echo technique. The precision was ± 1%. The isotherms show the now familiar broad maximum below ≈ 308 K. The ratio of DS(H216O) to DS(H218O) is constant over the whole region studied and is equal to [m(H218O)/m(H216O)]½. Comparison of the self diffusion data with tracer data for HTO in water show the data to be consistent with a slightly greater coupling of translational and rotational motion of HTO relative to H2O in pure water at low pressures, i.e. the pressure dependence of DS is less marked for H2O, though the effect is rather small.

Self-diffusion in a dense hard-sphere fluid: A molecular dynamics simulation

Molecular dynamics calculations of the ratio D/DE (where D is the self-diffusion coefficient and DE is the Enskog dense fluid diffusion coefficient) for a dense hard-sphere fluid, have been done for the density range corresponding to 1.5 ⩽ V/V0 ⩽ 4.0 (where V0 is the volume of close-packed hard spheres), for systems of 128, 250 and 432 particles. Values of D/DE at a given density do not differ significantly for 250 and 432 particles, and the values are significantly smaller than those obtained for the same densities by Alder, Gass and Wainwright via application of a hydrodynamic correction to give values for an infinite number of particles.

Temperature and density dependence of the selfdiffusion coefficients of liquid n-octane and toluene

Selfdiffusion coefficients determined by the NMR spin-echo technique are reported for n-octane (-25–75°C, 0·1–361 MPa) and toluene (-50–50°C, 0·1–369 MPa). In the case of toluene, these are supplemented at 25°C by 14C radiotracer diaphragm cell measurements. The results for each substance are correlated with high pressure viscosity data. Those for toluene overlap the range of applicability of the rough hard sphere model, and this model is used to compare the transport properties of toluene with those of benzene and mesitylene.

Thermodynamic and transport properties of 1,2-dichloroethane

Abstract(p, V, T) data for dichloroethane (DCE) have been obtained at 278.15, 288.15, 298.15, 313.15, 323.15, and 338.15 K for pressures either slightly below the freezing pressure or up to a maximum of 280 M Pa, together with densities at 0.1 MPa. A high-pressure self-centering falling-body viscometer method has been used to measure shear viscosities at 278.15, 288.15, 298.15, 313.15, and 323.15 K for pressures either slightly below the freezing pressure or up to a maximum of 330 MPa. Self-diffusion coefficients for DCE are reported at 278.15, 288.15, 298.15, and 313.15 K for maximum pressures up to 300 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The shear viscosities and self-diffusion coefficients have been interpreted in terms of a modified rough hard-spheres theory. The anomalous behavior observed for p-V-T, shear viscosities, and self diffusion at higher temperatures and pressures is suspected to be the result of temperature and pressure altering the population ratio of the two molecular conformers, trans and gauche.

Shear viscosity of methanol and methanol + water mixtures under pressure

Shear viscosities have been measured for methanol up to 400 MPa at 298, 313, and 323 K and for methanol-water mixtures (a) at 0.1 MPa and 278 K and (b) up to 300 MPa at 298 K. Where a comparison is possible the results are in good agreement with literature data. The data for the mixtures are discussed in terms of hydrogen bonding in methanol and water and by the use of excess viscosities.

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.

High-precision measurements with a bellows volumometer

A metal bellows volumometer operating to 250 MPa is described which uses a linear differential transformer in a novel, indirect way to establish the position of the moveable end of the bellows with a precision of about 1 in 60000. Calibration with both water and n-heptane has shown that the effective cross-sectional area of the bellows depends on both pressure and the extent of movement of the bellows. Comparison of excess volumes for acetonitrile-water mixtures calculated from the bellows volumometer data with values determined directly by other authors indicates that the device provides densities accurate to +or-0.02%.

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.

Diaphragm cell for high-temperature diffusion measurements. Tracer Diffusion coefficients for water to 363 K

A modified diaphragm cell for diffusion measurements at high temperatures is described. It has been used to obtain tracer diffusion coefficients for 3HHO and H218O in water from 298 to 363 K. Where comparisons are available, the results are in good agreement with literature data. The data have been converted to self-diffusion coefficients of water and combined with existing data to provide a series of equations covering the temperature range 242–498 K.

Volume ratios {V(p)/V(0.1 MPa)} for n-heptane at temperatures from 278 K to 338 K for pressures up to 400 MPa

A bellows volumometer has been used to obtain volume ratios relative to 0.1 MPa for n -heptane at (278.15, 288.15, 298.15, 313.15, 323.15 and 338.15) K for pressures up to 400 MPa. A version of the Tait equation of state enables accurate extrapolation of the results to 198 K and to 363 K. Prediction of volume ratios with reasonable accuracy up to 423 K is possible if parameters of the critical point are included in the Tait equation. The isothermal compressibilities, isobaric expansivities, “internal pressures”, and changes in isobaric specific heat capacity, have been evaluated from the results.