Wittko G, Köhler W
Physikalisches Institut, Universität Bayreuth, 95440 Bayreuth, Germany.
Eur Phys J E Soft Matter. 2006 Dec;21(4):283-91. doi: 10.1140/epje/i2006-10066-4. Epub 2007 Jan 22.
The mutual mass diffusion coefficient (D) and the thermal diffusion coefficient ( D (T)) of the liquids acetone, benzene, benzene-d1, benzene-d3, benzene-d5, benzene-d6, 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 degrees 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.
采用瞬态全息光栅技术，在25℃的温度下，测量了丙酮、苯、苯 - d1、苯 - d3、苯 - d5、苯 - d6、苯 - 13C6、正己烷、甲苯、1,2,3,4 - 四氢萘、异丁基苯和1,6 - 二溴己烷在质子化和全氘代环己烷中的互扩散系数（D）和热扩散系数（D(T)）。质量扩散系数呈现出明显的浓度依赖性。环己烷的全氘代仅导致质量扩散系数的微小变化。如果溶质分子小于溶剂分子，斯托克斯 - 爱因斯坦方程能很好地描述极限示踪扩散系数。但它无法描述百分之几的小同位素效应。另一方面，与浓度无关的同位素效应与恩斯科格理论一致，该理论并未给出液体混合物质量扩散系数的绝对值。所有二元混合物的热扩散系数呈现出适度且几乎线性的浓度依赖性。其同位素效应，即环己烷氘代时D(T)的变化，随摩尔分数而变化。当环己烷被全氘代时，作用于环己烷中任何示踪分子的热泳力变化量相同，与氘代前热泳力的大小无关。这种热泳力的变化与在上述任何一种液体中作为示踪剂时作用于环己烷和全氘代环己烷的热泳力之差大小相等但符号相反。
