Influence of isotopic substitution on the diffusion and thermal diffusion coefficient of binary liquids |
| |
Authors: | G Wittko W Köhler |
| |
Institution: | 1. Physikalisches Institut, Universit?t Bayreuth, 95440, Bayreuth, Germany
|
| |
Abstract: | The mutual mass diffusion coefficient (D) and the thermal diffusion coefficient ( D
T) of the liquids acetone, benzene, benzene-d
1, benzene-d
3, benzene-d
5, benzene-d
6, benzene- 13C6, n-hexane, toluene, 1, 2, 3, 4-tetrahydronaphtalene, isobutylbenzene, and 1, 6-dibromohexane in protonated and perdeuterated
cyclohexane have been measured with a transient holographic grating technique at a temperature of 25 °C. The mass diffusion coefficient shows a pronounced concentration dependence. Perdeuteration of cyclohexane only leads to
marginal changes of the mass diffusion coefficient. The Stokes-Einstein equation describes the limiting tracer diffusion coefficients
well if the solute molecule is smaller than the solvent. It is not capable to describe the small isotope effect of a few percent.
On the other hand, the isotope effect, which is independent of concentration, is in agreement with the Enskog theory, that
does not provide the absolute value of the mass diffusion coefficient of the liquid mixtures. The thermal diffusion coefficient
of all the binary mixtures shows a moderate and almost linear concentration dependence. Its isotope effect, which is the change
of D
T upon deuteration of cyclohexane, varies with mole fraction. The thermophoretic force acting on any tracer molecule in cyclohexane
changes by the same amount when cyclohexane is perdeuterated, irrespective of the magnitude of the thermophoretic force before
deuteration. This change of the thermophoretic force is equal but of opposite sign to the difference between the thermophoretic
forces acting on cyclohexane and perdeuterated cyclohexane as tracers in any of the above liquids. |
| |
Keywords: | 66 10 Cb Diffusion and thermal diffusion |
本文献已被 PubMed SpringerLink 等数据库收录! |
|