Universal isotope effect in thermal diffusion of mixtures containing cyclohexane and cyclohexane-d12

Abstract

The Soret coefficients S(T) of the liquids acetone, benzene, benzene-d1, 1,3,5-benzene-d3, benzene-d5, benzene-13C6, benzene-d6, n-hexane, toluene, 1,2,3,4-tetrahydronaphthalene, isobutylbenzene, and 1,6-dibromohexane have been measured in protonated and perdeuterated cyclohexane by a transient holographic grating technique. It has been found that S(T) can be either positive or negative and even change its sign as a function of concentration. The isotope effect DeltaS(T)=-0.99 x 10(-3) K(-1), which is the change of S(T) after isotopic substitution of cyclohexane, neither depends on concentration nor on the nature of the mixing partner. Only in the case of the polar acetone is DeltaS(T) approximately 30% larger but still concentration independent. Based on the experimental findings, some general conclusions about the dependence of the Soret coefficient on molecular properties are drawn.

Mass Effect on Thermodiffusion using Molecular Dynamics

“…Among the effects that might affect thermal diffusion amplitude is the mass ratio between the species [1][2][3][6][7]. Quite surprisingly some of the usual thermodynamic models predicting thermodiffusion [8][9][10] do not take into account an explicit contribution of the mass effect apart from the one at low density.…”

Experimental investigation of the Soret effect in acetone/water and dimethylsulfoxide/water mixtures

“…14 Recently, special focus has been on the dependence of S T on parameters such as mass and moment of inertia. 6,11,12 For many associating liquids, where specific interactions such as hydrogen-bonding or electrostatic interactions exist, sign changes of S T with composition have been observed. 6,9,15,16 Molecular dynamics (MD) simulations have become an important tool in the investigation of thermal diffusion behavior of Lennard-Jones model fluids and small-molecule liquids.…”

“…6,11,12 For many associating liquids, where specific interactions such as hydrogen-bonding or electrostatic interactions exist, sign changes of S T with composition have been observed. 6,9,15,16 Molecular dynamics (MD) simulations have become an important tool in the investigation of thermal diffusion behavior of Lennard-Jones model fluids and small-molecule liquids. [17][18][19][20][21] Lately, the simulation techniques for non-equilibrium properties have been improved, which have led to a reasonable agreement between simulations and experiments for associating and non-associating liquid mixtures.…”

“…5 In the past the thermal diffusion behavior of simple fluid mixtures has been studied extensively. [6][7][8][9][10][11][12][13] Organic liquid mixtures have been used in a benchmark test, to establish reference data. 14 Recently, special focus has been on the dependence of S T on parameters such as mass and moment of inertia.…”

Systematic study of the thermal diffusion in associated mixtures

“…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. In order to study the influence of molecular mass more systematically binary mixtures of unpolar solvents with cyclohexane and its isotopes have been investigated 26 .…”