Thermodiffusion, molecular diffusion and Soret coefficients of aromatic+n-alkane binary mixtures

Abstract

In the present work, we have measured the thermodiffusion coefficient of 51 binary liquid mixtures at 25 C. These mixtures correspond to the series of the aromatics toluene and 1-methylnaphthalene with n-alkanes nCi (i = 6, 8, 10, 12, and 14) at different mass fractions in the whole range. For that, we have used the thermogravitational technique. It is shown that the thermodiffusion coefficient is a linear function of the mass fraction in all the mixtures. Extrapolating the lines, we obtain the thermodiffusion coefficient in dilute solutions of n-alkanes for both toluene and 1-methylnaphthalene. These limiting values show a linear dependence with the inverse of the product of the molecular weights. In addition, we have measured the molecular diffusion coefficient of all the mixtures at 0.5 of mass fraction and at 25C, by the sliding symmetric tubes technique. It is observed that the product of this coefficient with the viscosity at the same concentrations takes a constant value for each of the series considered. Finally, we have also determined the Soret coefficient of the equimass mixtures by the combination of the measurements of thermodiffusion and molecular diffusion coefficients.

An Unreasonable Universality of the Thermophoretic Velocity

“…To pursue this idea, we have determined the thermodiffusion coefficients of MN and BrN and of the halogenated benzenes FB, ClB, and BrB as solutes in n -alkanes as solvents in the limit of infinite dilution. Our own measurements are complemented by literature data for isobutylbenzene (IBB), MN, and toluene (Tol), also in alkanes.…”

“…Extrapolations for solvent molar mass M 2 → 0. Literature data from refs (Larrañaga) and (Furtado). The green diamond indicates the universal plateau value ηD T ∞ ≈ 6 × 10 –15 Pa m 2 K –1 .…”

“…Data for alkane mixtures calculated according to ref . Data for Tol are from ref (open squares) and ref (filled squares). Data for MN are from ref (open triangles) and own measurements (filled triangles).…”

“…Data for Tol are from ref (open squares) and ref (filled squares). Data for MN are from ref (open triangles) and own measurements (filled triangles). Data for cyclooctane are from ref (stars).…”