Thermal diffusion measurements and simulations of binary mixtures of spherical molecules

Abstract

Thermal diffusion forced Rayleigh scattering measurements on binary mixtures of carbon tetrabromide (CBr(4)), tetraethylsilane, and di-tert-butylsilane in carbon tetrachloride (CCl(4)) are reported at different temperatures and concentrations. The Soret coefficient of CBr(4) in CCl(4) is positive and S(T) of both silanes in CCl(4) is negative, which implies that the heavier component always moves to the cold side. This is the expected behavior for unpolar simple molecules. Both silanes have the same mass so the influence of the difference in shape and moment of inertia could be studied. For all three systems, S(T) decreases with decreasing CCl(4) concentration. The results are discussed in the framework of thermodynamic theories and the Hildebrand parameter concept. Additionally, the Soret coefficients for both silaneCCl(4) systems were determined by nonequilibrium molecular-dynamics calculations. The simulations predict the correct direction of the thermophoretic motion and reflect the stronger drive toward the warm side for di-tert-butylsilane compared to the more symmetric tetraethylsilane. The values deviate systematically between 9% and 18% from the experimental values.

Systematic study of the thermal diffusion in associated mixtures

“…The absolute value of the Soret coefficient was previously connected with the solubility parameter 21 . Mutually soluble components become undistinguishable, so that the Soret coefficient of such mixtures is equal to zero.…”

“…In the first group of mixtures the component with the larger mass or higher density moves to the cold side, and this effect becomes stronger if the components are less miscible [18][19][20][21] . This empirical observations still hold for some mixtures from the second group 18 such as benzene/carbon tetrachloride 22 and cyclohexane/carbon tetrachloride 23 while for systems benzene/cyclohexane 24 and benzene/alkanes 25 this approach fails.…”

Study of the Soret Effect in Hydrocarbon Chain/Aromatic Compound Mixtures

“…In our previous work 4 we have shown experimentally and by reverse non-equilibrium molecular dynamic simulation (RNEMD) that the binary mixtures of simple molecules (tetraethylsilane, di-tert-butylsilane and carbon tetrabromide in carbon tetrachloride) obey this rule of thumb.…”

Experimental approaches to study thermodiffusion – A review

“…In case of polar liquid mixtures, thermodiffusion is dictated by the interactions between the molecules. In LennardeJones fluids, the size of the molecules and their mass determine the direction of separation [35].…”